How to Buy Capacitors on Mouser.com

Posted on June 29, 2026 by retrovoltage

Buying parts for a project can be intimidating. Beyond just identifying what you need in the first place, you then have to navigate a maze of different suppliers. Who’s reputable? What do you avoid?

Boutique shops offering curated selections will probably have good quality components, but you’re going to pay more – and it might be hard to find in the first place. Rolling the dice with whatever you find on Amazon might be a more familiar search experience but you risk getting low quality, grey market, or counterfeit parts. The risk is even worse if you go with Aliexpress or similar! And the big, reputable parts houses which are used by professionals might be intimidating as they’re built for engineers working in the field.

With a little know-how, though, it’s actually pretty easy and you’ll get genuine, high quality components from the best suppliers, and you might even get a better price if you buy enough to get a volume discount which often starts as low as quantity 10 units.

In this guide, I’ll show you how to search for capacitors on Mouser, one of the leading parts suppliers, available worldwide. (I’ll cover searching for resistors, inductors, and some other things like searching for transistors and op-amps, in other posts and I’ll link those here when it’s ready. This is the first of the series.)

Why replace capacitors at all?

Many capacitors, especially aluminum electrolytics, have a finite lifespan. The electrolyte inside them slowly dries out over time, which causes capacitance to drop and ESR (series resistance) to rise. A capacitor with high ESR can no longer filter power supply noise effectively, which puts stress on other components downstream. It also generates internal heat, creating a vicious cycle which ultimately leads to component failure.

In audio equipment this shows up as hum, distortion, or loss of bass. In other gear it can cause erratic behavior, failure to start, or outright damage to other parts. Electrolytic capacitors in equipment from the older than the 2000s are often operating well past their design life, even if the device still powers on, and proactive replacement is usually cheaper and less frustrating than diagnosing the cascade of symptoms a failing cap can cause.

Electrolytic capacitors are probably the most common failure. Other types of capacitors can also fail but that’s usually either because they’re an archaic type (paper) or have been physically damaged.

In many repairs (but certainly not all), just replacing electrolytic capacitors is enough to bring a device back to life whether it’s an antique radio, a vintage stereo receiver, or a modern computer monitor.

Electrolytic Capacitor Basics

Since caps are probably the most common thing that’s needed, we’ll start here. You can jump directly to Mouser’s Capacitor search page. https://www.mouser.com/c/passive-components/capacitors/ There are a couple more clicks you cna use to drill down a bit from there before going for spec selection.

You’re likely going to see Aluminum electrolytic, ceramic, and film capacitors – and many more electrolytics than any of the others. These three types cover the vast majority of what you’ll encounter in consumer electronics, and they each have a distinct job. (If you’re working on more digital electronics, for some reason those tended to use tantalum electrolytic capacitors – you can replace those with an aluminum electrolytic you find using the instructions here as well.)

Aluminum electrolytics are the cylindrical cans you see everywhere, and they’re built around a liquid or gel electrolyte soaked into aluminum foil. They’re cheap to make at high capacitance values, which is why they dominate in power supply filtering and audio coupling stages, but the electrolyte can dry out or vent over time, which is why they’re the most common failure point you’re likely to encounter when repairing older gear.

Chemical residue under removed electrolytic capacitors in a Bose equalizer

Axial vs. Radial Lead Electrolytic Capacitors

The difference here is purely physical. An axial capacitor has one lead coming out each end, like a little barrel or torpedo, and they tend to show up in older equipment designed for hand-wiring or older PCB layouts where components lie flat. A radial capacitor has both leads coming out the same end and stands upright on the board, which is how most modern electrolytic capacitors are packaged. When you’re doing a replacement, you almost always want to match the footprint on the board. You can sometimes get away with replacing a radial lead cap with an axial lead capacitor by bending a lead around (although why you’d want to is another question, as axial lead caps are more expensive) but if you replace an axial lead cap with a radial lead by splaying the legs wide you’ll stress out the seals where the leads exit the case and it can lead to premature failure.

Snap-In and Screw Terminal Electrolytic Capacitors

Axial and Radial lead capacitors are typically solder-in, smaller lead sizes. If you’re working in the main power supply of something which has a fair amount of power output, like a 100W power amplifier, you’re going to find some bigger capacitors. In the Search screen, those would be the Snap-In or Screw Terminal capacitors.

These are both formats for large electrolytic capacitors that are too big to be held in place reliably by thin wire leads alone. Snap-in capacitors have extrapins spaced to fit into PCB holes that are soldered in but not connected to anything, providing extra mechanical support.

Screw terminal capacitors are even larger and are meant to be bolted to a chassis or bus bar and connected with wires or lugs, rather than mounted to a PCB at all. They’re common in industrial gear and high-powered audio equipment. If you’re replacing one of these, the pin spacing (for snap-in) is absolutely critical to match. Screw terminal spacing (for screw terminal caps) should be matched as closely as possible, but you genreally have a few mm of play in wire leads attached that way to adjust for slightly different manufacturing sizes.

Sometimes, in an older amplifier, you’ll see large cans clamped in but they use pins. I tend to replace these with screw terminal capacitors, and add extra ring terminals to the wire terminations. It’s easier to solder, and easier to service if it needs more work in another few decades. More than anything, though, that’s an aesthetic preference more than a functional one.

Polarized vs. Bi-Polar / Non-Polar Electrolytic Capacitors

Most aluminum electrolytic capacitors are polarized, meaning they have a positive and a negative terminal and must be installed the right way around or they’ll fail, sometimes dramatically.

Bi-polar (also called non-polarized electrolytic, or NP) caps are built so that either lead can go to either polarity, which makes them useful in applications where the voltage across the cap is AC or where the polarity is otherwise unpredictable. Bipolar caps turn up often in speaker crossovers, or interstage coupling.

You can always replace a polarized capacitor with a non-polarized capacitor (although an NP cap might be a little big larger physically) but if you replace an NP cap with a polarized one, there’s a good chance that it’ll fail and end up as a short circuit between places that shouldn’t be connected with a DC voltage.

One thing to note: if you are actually replacing crossover capacitors inside a speaker, I recommend shopping from a site that sells crossover components instead. There’s a couple of things to get wrong here, since crossover components are handling real current, not just voltage. At the very, very end of this article I have a short note that talks about this and where to go for parts; that’ll be the subject of a separate article in the future as well.

Brands

Mouser helpfully lists some of the most popular brands, and you’ll generally find what you need within any of these.

If you’re in doubt, Nichicon caps are always a good choice. They’re a Japanese brand, highly regarded and often used in audio equipment from the factory. For screw- and snap-in capacitors, you’ll probably find what you need in a KEMET, Panasonic, or Cornell Dubilier / Knowles capacitor.

More important than the brand is selecting the right specs for the application., which you’ll do through the interactive search form.

Searching for Radial Aluminum Electrolytic Capacitors

This all applies to Axial, if you click Axial instead of Radial on their web site. As you’re searching, make sure that “Smart Filtering” is checked, and I recommend selecting both “In Stock” and “Normally Stocked” below. These will ensure you’re seeing results you can buy, and that the display will update and narrow your choices as you move through the selections.

The same general idea applies to all the other types of capacitors as well, which I cover a bit later in this article, but in somewhat lesser detail since most of it is the same. Keep on reading to learn about Snap-In / Screw Terminal, as well as Ceramic and Film capacitors.

From (mostly) left-to-right:

Capacitance

The capacitor value is typically printed on the side, next to the voltage. In this case, we’re looking at a 2200 uF, 25V radial lead capacitor. When in doubt, pick the exact same capacitance as is listed on the part you’re planning to replace.

Older equipment was often built with capacitor values that followed older preferred-number series, so you’ll sometimes see values like 5 µF, 8 µF, or 25 µF on a schematic that don’t match anything currently in production. Modern capacitors are manufactured to the E-series, where the standard values near those are 4.7 µF, 10 µF, and 22 µF.

In almost all practical applications, a 4.7 µF cap is a correct replacement for a 5 µF cap, and a 22 µF works where 25 µF was specified. The tolerances on most capacitors are wide enough (often plus or minus 20%) that the circuits were never relying on the exact value anyway. If you’re ever unsure, the datasheet or schematic context will usually make clear whether the application is precision-critical (very rare) or just general use.

If you’re not sure yourself, here’s a chart that can help you pick the best modern replacement from an old value. The Series shows you which group it’s from — this is just for reference. “E6” means that series between 1 and 10 has 6 values, and with a 20% tolerance, this is enough to cover all possibilities. “E12” is a 10% tolerance, needing 12 different values to cover the range. “E24” is a 5% tolerance, and so on. (Resistors go higher, with E48 for 2%, E96 for 1%, or E192 for 0.5% — but electrolytic and film capacitors aren’t built to such tight tolerances.)

Electrolytic capacitor applications are typically pretty forgiving. Stay close to the original value and you’re fine.

Voltage

The voltage rating on a replacement cap must meet or exceed the original. Going lower risks premature failure or outright failure on startup. What’s less obvious is that going higher (within the same physical footprint) is actively good for longevity. A capacitor running at 50% of its rated voltage will outlast one running at 80-90% of its rated voltage by a significant margin, because the electric stress on the dielectric is lower.

Modern manufacturing has made higher-voltage caps in compact sizes more accessible, so it’s often possible to fit a 50V or 63V cap into a spot that originally held a 35V part, with no downside. Just verify the physical dimensions still fit before ordering.

You can see how, just by selecting the brand, capacitance, and voltage (I’m going up to 35V in this example) we’ve narrowed it down from 11,023 in-stock options to just 38.

Diameter, Length, and Lead Spacing

These are obviously the physical dimensions of the capacitor. You can be a bit flexible with length and diameter: many modern replacements are going to be considerably smaller than whatever was there before, and the gap grows the older the original part. Your replacement might be smaller, but if you have the room for it, there’s no reason you can’t go a bit bigger as well. In most cases, you can leave the diameter and length blank and do a quick check before purchase that it’ll fit.

Lead spcaing is a bit more important. Perfect spacing between holes is great, but you can go 1-2mm in either direction without much issue. If you go smaller, you can slightly bend the legs apart; wider, slightly bend them together. If you do this, though, leave a gap at the base so you don’t end up doing a tight pinch where the leads exit the case – this can damage the seals and lead to premature failure. (A coin’s height or two is just fine here.)

Life & Temperature

The design lifetime for capacitors – ranging from 1000 hours to tens of thousands – represents the mean time before failure of a capacitor run at 100% of its rated voltage and temperature. Your actual working lifespam will be greater if you’re running them de-rated in either direction. Going up a size or two in voltage, and selecting 105°C temperature rating, will potentially extend the lifespan by an order of magnitude or even more.

As such, I typically don’t select a value for Life, but I do pick one for temperature. Then when I get to the final set of selections, I’ll confirm that I have something reasonable but otherwise don’t worry about it too much.

Product

These designations are partly meaningful and partly marketing. Unless otherwise specified, you’re probably fine with “General Purpose Electrolytic Capacitors”, but you can occasionally get better performance (especially in audio and RF circuits) by selecting “Audio Grade” or “Low Impedance” electrolytic capacitors, respectively.

“Computer grade” typically means the capacitor is rated for higher ripple current and has a longer specified lifespan (often 2000 hours or more at rated temperature), reflecting the demands of server power supplies and PC motherboards that run continuously.

“Audio grade” is squishier and varies by manufacturer, but it generally implies tighter tolerances, lower ESR (equivalent series resistance), and sometimes specific construction choices that the manufacturer claims reduce distortion or noise in audio circuits. Whether the latter makes an audible difference is a subject of genuine argument, but the lower ESR and higher quality control can have real engineering benefits.

When you’re doing a straight repair, a reputable standard-grade cap from a known manufacturer (Nichicon, Panasonic, Rubycon, etc.) is usually all you need. Spending extra on audio-grade parts makes the most sense when you’re restoring something where the signal path capacitors are directly in the audio chain, or something especially high-end, but in most pieces of vintage gear you’d struggle measure with test equipment – let alone hear – any actual difference given the construction quality is so much higher today.

So, I’ve selected:

Nichicon
2200 uF
35VDC
(Diameter, Length, and Lead Spacing all blank)
General Purpose
(everything blank up to Temperature)
105C

That’s much more manageable! Hit “Apply Filters” to update the listing below.

Packaging

Now, we’ve got just 3 options.

Price	Length	Lead Spacing	Life	Ripple	Temp	Packaging
$2.41	20mm	7.5mm	5000 H	2.64 A	105°C	Bulk
$2.03	20mm	7.5mm	2000 H	—	105°C	Ammo
$1.85	25mm	7.5mm	1000 H	1.26 A	105°C	Ammo

“Bulk” means they’ll arrive in a bag, loose. “Ammo Pack” refers to them coming folded in a small box if you buy a full Reel, where they come with the leads taped onto a perforated paper strip at even intervals suitable for a manufacturing robot on an assembly line.

They’re all about the same size. I generally prefer to get the ones with the highest Ripple capacity – which also relates to lifespan – just to be entirely sure I’ll never be in there again. But if you know the capacitor is only filtering power for a few smaller transistors, or is only in the signal path, you can go with a lower figure that’s cheaper. (Recall, running these de-rated drastically extends the lifespan. The “1000 hour” capacitor, upsized to the next voltage level and running at 65C instead of 105C, might easily last for up to 50,000 hours of normal operation.

The “Availability” column on the page tells you whether they’re in stock, and how many.

Click on the hyperlinked Part Number in the left column to go to the detail page.

You’ve got the pricing breakdown here:

And you’ve got the full specs:

If you especially wanted, you could view the full datasheet as well. Go ahead and enter your desired quantity, it’ll tell you the price, and then hit “Buy” to add to cart.

It’s a good idea to pick up a few extra in case you damgae one or need an extra, especially if you’re close to a price break. For example, ordering 3 more capacitors:

The price you pay for 3 more capacitors, including tariff, only ends up being 14 cents more. It’s worth the peace of mind – and the single shipping price.

Screw Terminal Electrolytic Capacitors

Now, for main power supply electroltic capacitors, you’re looking at stuff that’s bigger than a roll of quarters – like these two main power supply capacitors in a Marantz Model 22 which I fixed up back in 2017:

They’re clamped in on top, and have solder tabs on the bottom.

Searching for a replacement is pretty similar, but you need to pay a bit more attention to the physical dimensions. The capacitance value is typically a little more flexible here.

The main filter caps are going to be very large capacitance values. In this example: on the left, the original 4,700 uF / 50V; on the right, a modern manufacture 4,700 uF / 63V capacitor. When in doubt, as always, replace with an identical capacity value and a higher voltage. If you can’t find one at a reasonable price or the correct size, it’s usually OK to go to a higher value – up to 50% higher should never be a problem for a power supply application.

One thing to note: I recommend that, where possible, you should replace solder tab capacitors (the old style above) with screw terminals. Solder tab caps had solder points on the bottom where you’d wrap a wire through and solder it on directly much like any other component. Screw terminal capcaitors are what they sound like.

Electrically, it’s identical. But it means that (1) you can remove and replace them more easily in the future, (2) you don’t have to worry about lead spacing as much, and (3) you’re not soldering the capacitors directly so heat damage isn’t going to be a problem. Because of the number of wires and size of the terminals, you’d otherwise have to hold the soldering iron there for longer, and that’s always a risk of cooking it from heat if you go over.

Solder tab capacitors do still exist, but they’re getting pretty uncommon these days. This replacement is functionally identical, slightly safer, and future-proof.

When searching for screw terminal capacitors, the physical diameter matters a lot. You need to make sure you’re pretty close to the size of the ones you’re replacing. Length doesn’t matter much, and lead spacing should be vaguely close, but the mounting clamps won’t hold it properly if it’s too small or too big. You can squeeze a few mm in either direction but that’s about it. I also typically leave the Manufacturer blank here.

Prices vary quite a bit, but clicking on the part number will give you the same info as an axial/radial capacitor. Find one which looks good to you, double-check the detail page, and add to your cart.

Snap-In Electrolytic Capacitors

Snap-ins are what you’ll find on later, PCB-era gear starting in about the ’80s:

Failed snap-in capacitors in a Yamaha C-80 pre-amp.

They have the typical polarized terminals for + and – and may have several physical tabs only in addition to the electrical contacts.

For a snap-in capacitor, you need to be a bit more exacting. These are a bit more challenging to replace, especially if you’re new to the hobby.

The new component needs to have similar physical dimensions to fit in the space available – which is often a bit more constrained. In the photo above, there was only a gap of a few mm between the top of the existing caps and the case of that Yamaha C-80. You also need identical Lead Spacing between the + and – ports, and the pin arrangement needs to match. (Common schemes include 2, 3, 4, or 5 pins.) For these, if you’re not sure, you probably want to take a look at the datasheet for physical details. Here’s an example: https://www.mouser.com/datasheet/3/508/1/ALF70G102EH450.pdf

In this view, we have (D)iameter, (L)ength, Lead (S)pacing, (L)ead (Length), and (F)it which is the individuall ead size. Make sure to do careful measurements – if you know what you’re doing, you can sometimes use something like a carbide PCB drill bit to make a modification but at that point you’re doing surgery and not just a component replacement.

Some of the earliest types of snap-in caps use what we’d now consider non-standard pin arrangements. If you’re in doubt, when replacing PCB-mount snap-in capacitors, ask an expert for help. (Audiokarma forums are a good place to start, or one of the Audio Repair or Electronics Repair communities on Reddit.)

Search using the same selection boxes, but fill in more of them. Carefully measure the space you have to work with, and the old caps, then select capacitance, voltage rating, length, diameter, lead spacing, and

Film Capacitor Basics

Film capacitors use a thin plastic film as the dielectric instead of an oxide layer or a ceramic material. They’re non-polarized, they have very low internal resistance and leakage, and they’re extremely stable over time because there’s no electrolyte to dry out or degrade. A film capacitor from the 1970s that hasn’t been physically damaged will still measure close to its original value and they generally don’t need to be replaced. The tradeoff is size: film capacitors are bulky compared to an electrolytic of the sme size, which is why they’re typically used in the nanofarad to low microfarad range rather than the hundreds of microfarads you’d get from an electrolytic of the same footprint.

Film capacitors show up most often in places where stability and low distortion matter more than raw capacitance. In audio equipment that means coupling capacitors in signal paths, tone stack components, and speaker crossover networks. They’re also the standard choice for snubber circuits (used to suppress voltage spikes across relay contacts and switching transistors), motor run capacitors in AC motors, and in some timing circuits – although you often see a ceramic or mica in those applications too.

In many cases, if you have the physical space for it, you can replace a polar or non-polar electrolytic capacitor with a film cap. Speaker crossovers, coupling caps, tone capacitors, etc. are good applications for this. “Back in the day” you might have seen more electrolytics here – even in tiny values like 0.47 uF – because of physical size constraints; modern film caps are build smaller and tighter than they were 50 years ago (just like electrolytics) and so you have more flexibility these days.

It’s a subject of debate whether a film cap will “sound better” than an electrolytic cap in the same circuit. In most cases, and in most equipment, the answer is probably no: the limiting factor is probably circuit design. Entry-level gear, or guitar amps that aren’t built for fine hi-fi reproduction, probably won’t benefit. Very nice, high-end hi-fi amplifiers might.

Searching for Film Capacitors

Start your search similarly as any other type of capacitor. Go to the Film Capacitors page, and then click through to the selector. Remember to check “In Stock” and “Normally Stocked” at the bottom. I typically buy WIMA, Panasonic, or Nichicon (listed in the A-Z section) capacitors, but any of the Most Popular options are going to be juts fine.

Select voltage and capacitance. Note that film capacitors do come in very tiny (pF) values, so you’ll have to scroll a bit. The two real key pieces to note are the termination style and the dielectric.

Make sure to select “axial” or “radial” for termination style. We learned about those two termination styles up earlier with electrolytic capacitors. There are a few more options here and you want to make sure you get the right one.

One thing to note with the leads: many of these come with pre-cut leads that are only a few mm long, for sticking through a circuit board and only barely poking out the other side. This is fine if the lead spacing is exact, but if you’re going to be slightly bending the leads to fit (or if you’re repairing something with point to point wiring where the leads are strung between tie points) these won’t work well. Make sure to take a look at the pictures and the datasheet to confirm.

Tiny, PCB leads – might be OK, but worth double-checking.

The dielectric is also somewhat important here. The most common types you’ll encounter are polyester (often labeled PET or branded as Mylar) and polypropylene (PP). Polyester is cheaper, and it’s perfectly adequate for the majority of repair work: power supply bypassing, general filtering, motor applications, and anything where the capacitor isn’t directly in the audio signal path. Polypropylene has lower dielectric losses and a property called lower dielectric absorption, which means it releases stored charge more completely and doesn’t subtly “smear” rapidly changing signals. That makes it the preferred choice for audio coupling and crossover capacitors in anything where you care about sound quality.

If you’re restoring a piece of audio gear and you’re replacing capacitors that sit in the signal path, spending a little more on polypropylene is worth it, not because the difference is dramatic, but because it’s the right part for the job and it will outlast the equipment. (In a lot of older gear, though, they used cheap caps in every position so you might actually see some minor benefits to sound quality and accuracy here.)

Avoid a paper dielectric. These might not have the same reliability issues as older paper capacitors, but outside of boutique applications that are (in my opinion) backed more by superstition than science, they’re going to add cost and potential failure down the line compared with a PET or PP capacitor.

Filter, double-check the product detail pages, and buy as above.

Ceramic Capacitor Basics

Ceramic caps are probably the more complicated of these types of capacitors you might replace. The good thing is this shouldn’t come up very often: they’re typically the most stable, and will only be a problem if they’re either very old. From the 1960s or before, the packaging used just wasn’t as sealed or reliable as it was from the 70s onward, and this could lead to failure over time. Otherwise, though, failure is typically due to one of the same reasons a film cap might fail: either physical damage, or heat damage from something nearby – like being too close to a heat sink, or to a resistor which burns up for another reason.

Ceramic caps are complicated because ceramic capacitors come in two broad classes with very different behavior.

Class I ceramics, identified by codes like C0G or NP0, are precision parts: their capacitance stays essentially flat across temperature and voltage, they have very low losses, and they’re stable over time. They’re excellent for high-frequency bypassing, RF circuits, and timing applications where accuracy matters, and they have no meaningful drawbacks beyond the fact that they only come in small values, typically a few hundred picofarads at most.

Class II ceramics are a totally different. Codes like X7R, X5R, or Y5V indicate that the capacitor uses a high-permittivity ceramic formulation that allows much higher capacitance in a small package, but at a significant cost: the capacitance is sensitive to both temperature and applied voltage, and can drop by 20 to 80 percent under normal operating conditions depending on the grade. A 10 µF X5R capacitor rated at 10V might actually measure closer to 3 or 4 µF when 8V is across it. In audio applications, this voltage dependence is particularly problematic because it means the capacitance is changing in response to the signal itself, which introduces distortion. Class I ceramics (C0G or NP0) don’t have this problem, but they top out at small values. If you’re replacing ceramic capacitors, you should really replace like-for-like exactly as much as possible because of where they turn up.

In general, try and avoid replacing ceramic caps unless you know for a fact that it’s bad. Disc caps in older equipment are one thing, but RF circuits – especially in vintage gear – might have had dogbone or tubular ceramic caps, like these:

or an unusual dielectric (N750L) which is difficult if not impossible to find these days. Replace them at your own peril: you’re likely to end up with a tuned circuit which needs to be realigned at a minimum, or just drifts unpredictably it operates, leading to things like stations wandering around the dial and having difficulty tuning.

Fortunately, these are very unlikely to fail so just ignore them. Stick to doing as little as possible with ceramic caps, and unless you know exactly what you’re doing, only replace any ceramic disc capacitors and nothing else only when needed.

C0G/NP0 capacitors only come in small values. If you need something bigger for some reason, use a film capacitor.

Searching for Ceramic Capacitors

Skip any of the other options and go directly to Ceramic Disc Capacitors: https://www.mouser.com/c/passive-components/capacitors/ceramic-capacitors/ceramic-disc-capacitors/

Make sure to select C0G (NP0), but otherwise just pick the right voltage rating and capacitance. Any brand will do here. Confirm by viewing the datasheet, then buy just like we’ve seen above.

Speaker Crossover Capcaitors

Speaker crossover capacitors are a bit of a special case: they’re handling a fair amount of both voltage and current, which are rapidly changing with the signal, and they’re in a sound-critical part of the signal chain.

At a minimum, this means you need non-polar electrolytic capacitors. Better speakers will use film capacitors like polyester in the crossovers to route the different frequencies correctly between woofer, midrange, and tweeters (or more.)

Regardless of which type of capacitor you want to replace, I do recommend a specialized parts supplier for crossover caps, as they’ve done a lot of the research and selection work for you.

Rebuiding speaker crossovers isn’t something I’m going to get into in this article, but if you’re looking for a good place to shop, I often buy from Parts-Express (https://www.parts-express.com/speaker-components/crossover-components/crossover-capacitors) when I need something in this area.

Conclusion

I hope this has been helpful to learn how to shop on Mouser for your capacitor needs. I found that site pretty intimidating when I was first starting out in this hobby about 20 years ago, but now it’s like second nature.

Look for other articles in this series about buying other types of components soon!

Posted in Uncategorized | Tagged capacitor, diy, electronics, electronics repair, engineering, repair, restoration, shopping, Technology | 1 Comment

The Speaker Spotter — June 26, 2026

Posted on June 26, 2026 by retrovoltage

A recurring feature curating interesting speakers for sale on Craigslist from around the Pacific Northwest. Links to Craigslist postings might go down at any time if they’re sold or pulled from sale. We’re a little lighter this week with only 8 listings, but they’re a pretty interesting set. Take a look:

Polk SDA SRS 3.1 TL Speakers

$750 · Chattaroy (Spokane)

The SDA SRS 3.1 TL represents the final evolution of Polk Audio’s legendary Stereo Dimensional Array technology — an innovative system that uses a dedicated channel of audio sent to the inner edge of each speaker to cancel inter-aural crosstalk, producing a dramatically wider and more enveloping soundstage. This particular pair has received the seller-endorsed upgrades sanctioned by Polk engineering: revised tweeters, crossover improvements, and cabinet reinforcement, making these the most dialed-in version of a speaker that audiophiles regard as uniquely musical and non-fatiguing.

JBL Lancer 77 Speakers

$525 · Portland – Sauvie Island (Portland)

The JBL Lancer 77 is a beloved 1960s two-way floor speaker featuring the original LE10A woofer and LE20-1 tweeter — the same driver family found in far more expensive JBL studio monitors of the era. This pair has been professionally refinished in walnut with all original drivers and crossovers intact and functioning, plus the grilles (which typically show up damaged) described as excellent — a genuine rarity for this model at $525.

Monitor Audio-Silver 300

$1,000 · Walla Walla (Tri-Cities)

Monitor Audio’s Silver 300 is the flagship of the British company’s Silver line, a three-way floorstander with their signature C-CAM (Ceramic-Coated Aluminium/Magnesium) drivers and a dedicated Gold Dome tweeter. This sixth-generation pair is in the premium Rosenut real-wood veneer and has barely been used — the seller claims approximately 30 days of play — making it a rare opportunity to buy near-mint at a significant discount to the $2,000+ retail price.

Marantz Imperial 6-G Speakers

$100 · Ballard (Seattle)

The Marantz Imperial line was the company’s foray into speaker manufacturing in the late 1960s and early 1970s, bearing the Marantz name at a time when that meant uncompromising audio quality. This pair retains its original crossovers but has been modified by a previous owner with GRS 10PF-8 woofers and generic tweeters; the seller notes the tweeters should be replaced, which represents a straightforward restoration opportunity on freshly refinished cabinets for just $100.

Vintage Bose 901 Series 1 Stereo Loudspeakers Rare

$195 · olympia / thurston (Seattle)

The Bose 901 Series 1, introduced in 1968, was a genuinely radical design: nine full-range drivers per cabinet, with eight firing rearward and only one forward, intended to replicate the ratio of direct to reflected sound in a concert hall. These early cloth-surround examples from the early 1970s represent the model at its most collectible and are, I think, the most attractive of the series. You do need the Active Equalizer for best results (read all about that here https://retrovoltage.com/2026/06/12/everything-to-know-about-bose-901-series-i-and-series-ii-active-equalizers-speaker-systems-and-the-800-too/ ) but the Series 1 and 2 use cloth surrounds on the drivers, not foam, so they never need to be refurbished unless they have sustained physical damage. These are only $195, looks like a great deal to me.

Focal Chorus Center Channel Speaker

$300 · Otis Orchards (Spokane)

Focal’s Chorus line brought the French company’s audiophile driver philosophy — including the distinctive inverted-dome tweeter and polyglass mid-bass cone — to a more accessible price point, and the CC700V center channel was a standout performer in that lineup. The Walnut-enclosed cabinet and 91 dB sensitivity make it an easy load for most amplifiers; listed in immaculate condition at $300, it’s a solid deal for anyone building out a Focal-matched system or simply wanting a high-quality center channel.

Verdin church tower clock loudspeaker bell toller

$400 · Indianola (Seattle)

Verdin, founded in 1842 in Cincinnati, is one of the oldest bell and clock manufacturers in North America, and their tower loudspeaker systems were designed to project convincingly across large outdoor spaces — church campaniles, town squares, and university campuses. This 1990s set of four Verdin horn-loaded drivers with the original time-and-bell controller and amplifier was pulled from a working tower clock installation; it’s an extraordinary piece of audio history for $400, and the acoustics of those horns are genuinely impressive. It’s not exactly hi-fi, but these were unusual enough to make the cut for this issue.

Vintage light-up speaker, Mardi-Gras technology

$100 · Corvallis

An intriguing mystery piece from the 1970s: a party speaker with built-in lighting effects (also called a Color Organ) made by Mardi-Gras Technology — a now-obscure manufacturer that produced novelty audio equipment for the disco and lounge market. The seller knows little about its provenance other than it came with the house, and that’s half the appeal — this is the kind of find that rewards an afternoon of research and may turn out to be a genuinely rare survivor of that era’s more playful approach to speaker design. It might be an interesting center channel in a vintage system next to some Sansuis.

Posted in Audio, Speakers | Tagged craigslist speakers, music, old speakers, Speakers, Technology, vintage, vintage audio, vintage speakers | Leave a comment

The Speaker Spotter — June 19, 2026

Posted on June 19, 2026 by retrovoltage

Vintage Bozak B302A Speakers – Excellent

$500 · West Linn (Portland)

Bozak is an American loudspeaker legend, and the B302A exemplifies their philosophy: a 12″ B-199A woofer, B-209A midrange, and an array of B-200y tweeters carefully arrayed for wide, even dispersion and a notably natural tonal balance. Rudy Bozak’s speakers were hand-built and highly regarded by studio engineers and audiophiles alike. These do admittedly look a bit more like end tables than high end speakers, but they have a good reputation.

Pair of Martin Logan esl x speakers 1200obo

$1,200 · Boise

Martin Logan’s ElectroMotion ESL X is a hybrid electrostatic speaker, pairing a large curved electrostatic panel (for midrange and treble) with a conventional dynamic woofer for the bass frequencies below 500 Hz. The result is the transparency, speed, and pin-point imaging electrostatics are famous for, without the full-range limitations of pure electrostats. At $1,200 OBO — roughly a third of its original retail price — this is a compelling entry point into planar sound. I know a friend with a pair of these and they’re incredible.

Polk Audio SDA1 Speakers

$550 · Boise

The Polk SDA1 was part of Polk’s revolutionary “Stereo Dimensional Array” lineup, which used a proprietary interconnect cable to feed a crosstalk-cancellation network between the speakers — effectively removing each ear’s ability to hear the opposite channel and producing dramatic, lifelike staging. The SDA1 is the entry-level model in this esteemed series, and this pair comes complete with the essential 20-foot interconnect cable at $550 OBO. Vintage Polk have a great reputation in a way modern Polk really doesn’t, these could be well worth it.

Polk Audio – Complete setup

$2,999 · Richland, WA (Tri-Cities)

A rare chance to acquire a complete Polk Audio SDA system from the brand’s 1985–91 golden era, headlined by the flagship SDA-SRS 2.3 towers alongside rear speakers, center channel, and powered subwoofer. The SDA-SRS 2.3’s proprietary crosstalk-cancellation technology is what hardcore Polk fans still consider the pinnacle of mass-market home audio engineering — this turnkey system at $2,999 is priced fairly for what’s included.

(Make Offer) Polk Audio Monitor 10B Speakers – Pristine Condition

$390 · Bellevue (Seattle)

Lots of Polk today. The Polk Audio Monitor 10B is a classic early-1980s three-way floor-stander that helped define Polk’s early reputation for high-value audiophile performance. This pair is described as pristine and 100% original, with close serial numbers and healthy butyl rubber surrounds — no foam rot — which is the critical detail with speakers of this era. Hard to find in unrestored, original condition like this.

Pair of Vintage Walnut Sansui SP-2000 4-way full range, 6-speaker

$225 · Bellingham

The Sansui SP-2000 is a remarkable 1969 four-way, six-driver floor-stander from Japan, housing a 12″ woofer, dual midranges, dual horn tweeters, and a super tweeter in a handsome walnut cabinet — plus rear-panel room equalization switches that were unusual for the era. At 45 lbs per cabinet and full of vintage Japanese engineering ambition, the SP-2000 was clearly built to impress, and at $225 it still does. Now, Sansui speakers were built for people who wanted the aesthetic first, so they’re not the absolute best sounding vintage speakers out there but paired with a vintage system they do sound great. (I’ve personally owned SP-2500s and SP-3500s at different times.)

Pair of Vintage Walnut SP-30 bookshelf speakers

$200 · Bellingham

The Sansui SP-30, also from 1969, is the compact sibling to the SP-2000: a 2-way bookshelf speaker with a 6.5″ woofer and a distinctive 2″ horn tweeter in the same walnut finish. These examples are in nearly mint condition with original box — a rarity for a 55-year-old speaker — and the seller notes they pair naturally with their SP-2000 listing, offering a way to build a period-correct Sansui system.

Unique Design Acoustics PS-10 Speakers

$240 · Sequim (Olympic)

The Unique Design Acoustics PS-10 is genuinely one-of-a-kind: a 1990 “point source” three-way with a 10″ woofer firing downward through a 1″ slot at the base, a 5.25″ midrange, and a tweeter with an adjustable brightness control, all in a rubber-faced, mirror-imaged pair designed to minimize diffraction. The seller’s description matches what little documentation exists online — these were a short-production curiosity that audiophile forums occasionally surface as a hidden gem.

Monsoon MM 700 Planar Desktop Speakers, Parts Only

$80 · Sherwood (Portland)

I don’t generally highlight computer speakers in this feature, but these are an exception. Monsoon’s flat-panel planar satellite speakers from the early 2000s are distinct from most low-end computer sets. This MM-700 2.1 set has one damaged satellite and is listed for parts, but the subwoofer and remaining hardware are functional; for someone with the right repair skills, this is a worthwhile restoration project at $80.

Definitive Technology Mythos Hi End 5 speakers set

$260 · Lynnwood (Seattle)

Definitive Technology’s Mythos series was the brand’s flagship lifestyle line, with each Mythos Two tower housing a built-in powered bass module and bipolar driver arrays that send sound both forward and backward for a spacious, room-filling presentation. This complete five-speaker set — four Mythos Two towers plus the Mythos Three center channel — in great working condition at $260 is strong value for a dedicated home theater or two-channel room.

Posted in Uncategorized | Tagged audiophile, Speakers, vintage speakers | Leave a comment

Everything to Know about Bose 901 Series I and Series II Active Equalizer Repair & Speaker Systems (and the 800, too!)

Posted on June 12, 2026 by retrovoltage

The Bose 901 Direct/Reflecting Speaker System is as polarizing as it is interesting, a unique system from the golden age of hi-fi experimentation. It’s less about perfect sonic accuracy and more about the experience of listening to your music. And that’s one of the things I love about it!

While cleaning up some of my archives to save cloud space, I found that I’ve serviced nearly 500 Active Equalizers which are the important heart of these speaker systems. I’ve distilled some of the knowledge from all of that experience here, to help anyone else who wants to keep these systems running, and get good info from someone who actually has any clue what’s going on.

There is a truly staggering amount of AI slop out on the Internet about these speakers, ranging from slightly wrong to utter nonsense. In contrast, this article was written by a human who has owned and listened to all of these systems, and serviced and studied hundreds of them over thousands of hours

This article covers the Bose 901 Series I and Series II Active Equalizers, along with their live-sound sibling, the Bose 800 Active Equalizer paired with the Bose 800 speaker system. Keep on reading for all of the details! I’ve even included direct links to buy all the parts you need for the 901s on Mouser.com.

Bose 901 Series I and II Background

Introduced in 1968, the Bose 901 Series I was possibly the earliest forray into the brief era of active-equalized speakers which also included some offerings from DBX, EV, and McIntosh (and probably others I’m forgetting!) Designed by Dr. Amar Bose, these speakers prioritized ambience and presence over strict accuracy. Based on research suggesting that most of the sound you hear in a live performance arrives indirectly through reflections, Dr. Bose designed the cabinet with nine small, identical full-range drivers instead of a traditional woofer or tweeter. Eight on the back, one on the front. Everything the same size with no distinct woofers or tweeters, and no crossover components inside.

To make the concept work, every 901 was paired with a dedicated active equalizer that dramatically reshaped the speaker’s frequency response. The equalizer really is necessary to get the best sound out of the system – and sadly, it gets lost or damaged a lot of the time. Without it, the midsized drivers don’t get the drive power they need on both the low and high ends of the frequency range to perform properly. You end up with the derrogatory description, “No Highs – No Lows” without it.

If you’re absolutely in a pinch, you can crank the bass and treble adjustments on your amplifier up as high as they’ll go, but the center frequency is off and the gain still low compared with the bundled EQ. If at all possible, find yourself a real one for best results.

Bose 901 Direct/Reflecting Speaker System – Series I and II

A pair of Bose 901 Series I speakers stacked togther with the equalizer on top. The equalizer is turned on and has a glowing power switch; the speakers are facing in the correct orientation with the flat side carrying the single driver facing towards the listener.

A rear view showing the same two speakers from the previous image, facing away.

The Series I and II are basically the same. They’re both solid wood with fabric covers. The flat side is the front side, with a single driver towards the top-right. (Some variants have a solid wood panel and only a small strip of fabric over the driver.) The diamond side, with 8 drivers split into two banks of four on each side, face the rear. You’ll typically want to put these 12-24 inches away from a wall. If you can find some with the original tulip stands, it really completes the look.

One of the great things about the Series I and II is that these early series used rubberized cloth surrounds, not foam surrounds as were used on the Series III and later models. As a result they’ll never need to be refoamed. There are also no crossover components inside, so no capacitors or anything to dry out and change the frequency response. All of that work is done in the equalizer.

You’ll want a pretty beefy amplifier for these to sound any good. While the specs say these 8 ohm speakers can be driven with a minimum of 25W, they’re rated for a maximum amplifier power of 270W RMS, and 400W peak power for under 5 seconds. And you definitely need it as the equalizer is applying +18 dB of gain to some frequencies, which comes out to about 63x the power. The midranges might get away with 2W, but with the equalizer’s gain would be asking for 126W at low frequncies which could push an underpowered amp into clipping, especially if you’re trying to listen at a high volume.

Bose 901 Series I Active Equalizer

Series 1 Early Production

The 901 Active Equalizer is an unassuming little box, and was sold worldwide (including for a great price at overseas military base exchange stores) so it turns up in both 120 and 240V versions. Each generation of 901 speakers had their own equalizer, starting with the Series I, which actually had two variations as the design went from prototype to mass production.

A wood case Bose 901 Series I active equalizer sitting on the workbench showing the front with controls.

The earliest versions had a solid wood case, which was really nice. Later versions of the Series I and then the Series II used a particle board case with a contact paper veneer. These actually don’t look bad if they’re in nice shape, but the adhesive comes apart as they age and the paper can delaminate, or the entire case can come apart. It’s especially prone to doing this if there’s any rough handling in shipping. (You’d be amazed at the number of people who used to send me equalizers tossed into a box with no padding whatsoever and left to bounce around!)

A particle board case, which was destroyed in shipping and the sides have snapped off and folded inward, held together only by the shielding tape on the inside cover.

The earliest models had screwed components, and the serial number tag was on the bottom instead of the rear.

A rear view of an early production Series I equalizer, showing that the rear panel jacks are screwed in rather than riveted in.

The production label on the bottom of the equalizer from the previous image. The label reads:

BOSE MODEL 901
Serial #230
Active Equalizer

Pat. 3,038,964
Pat. Pending

This was the earliest one I ever saw through my shop, Serial #230, and the owner described being an Electrical Engineering student at MIT who toured the factory with a class, and the kid ended up with a 901 system given to him by Dr. Bose personally. The factory switched to rivets after a few hundred units, probably in the #700s.

A rear view of a later, but still Early Production, equalizer which has switched to rivets. Serial number 06805.

There were two versions of the Series I, an “Early Production” model, and the main mass-production model. The early version is quite chaotic.

An inside view of the Series I Early Production equalizer, showing the original unreplaced components in chaotic alignment.

It’s fairly straightforward as far as the schematic:

The electrical schematic for the Series I Early Production taken from the service manual. — Bose 901 Series 1 Early Production Schematic – Click to Zoom In

Given the age, the Series 1 Early Production needs the most work. The Series I Mass Production model the second-most, and the Series II (of either variant) the least – but still needs basic service at a minimum.

For the Series 1 Early Production:

All electrolytic capacitors need to be replaced. I usually go up a level in voltage to improve longevity, since caps today are so much smaller. Axial capacitors – one lead on each side, rather than both leads on the same side – are a bit harder to find these days, but they’re out there. Replace the 500 uF with 470 uF, the new standard value. Replace the 5 uF outputs with 4.7 uF outputs, the new standard value.
Transistors will almost all need to be replaced. The pencil-eraser packages don’t hold up well and nearly every one of this series found multiple bad transistors. The originals are 2N3393. You can typically use a 2N5088 here if you want as well. (The mass production version, and the Series II, used 2N5088s.)
Replace the two diodes with 1N4007s, these two fail pretty regularly in this old style packaging. The new ones are much, much smaller.
Replace all of the film capacitors with identical values. These were often early paper-mylar caps and go leaky as well.
There are two 6.8V Zener diodes, which are in semiconductor packages where the third terminal is soldered to an anchor pad but is disconnected. These should also be replaced as well. You can use a 1/4W part here if you can find one. The 1N4954 is available on Mouser.
All of the resistors will have drifted, often outside of tolerance, but this isn’t the most critical thing. I replace them typically with 1% metal-film resistors but I’ll consider this step optional. Your channels may be a bit mismatched if you don’t replace the resistors, but it’ll run.

The neon bulb is often dead, too. If you can find an NE-2 bulb with current-limiting resistor that’ll fit, go for it, or you can get a 20V LED assembly with dropping resistor and power it directly from the first filter capacitor.

Here’s a list of the common parts for the Series 1 Early Production, and links to buy them at Mouser:

Description	Quantity
2N3393 Transistor	10
1N4007 Rectifier Diode	2
1N4954 Zener Diode	2
470 uF Axial Capacitor	2
100 uF Axial Capacitor	3
4.7 uF Axial Capacitor	4
3.3 uF Axial Capacitor	2
100 Ohm 1% Resistor	1
470 Ohm 1% Resistor	4
1K Ohm 1% Resistor	6
1.5K Ohm 1% Resistor	2
1.8K Ohm 1% Resistor	2
2.2 K Ohm 1% Resistor	5
3.9K Ohm 1% Resistor	2
4.7K Ohm 1% Resistor	2
10K Ohm 1% Resistor	8
22K Ohm 1% Resistor	4
39K Ohm 1% Resistor	4
56K Ohm 1% Resistor	4
150K Ohm 1% Resistor	2
274K Ohm 1% Resistor	2
1M Ohm 1% Resistor	2
0.015 uF Film Capacitor	6
0.047 uF Film Capacitor	2
0.1 uF Film Capacitor	4

(If you want to learn a bit more about buying your own parts on Mouser for other projects, I have an article about that, too.)

How to Buy Capacitors on Mouser.com

It’s not a bad idea to buy a few extras of each if you’ve got the budget, in case you clip something too short, mess up during installation, etc. Especially for the transistors and diodes. On the Zener diodes, since the new ones are only in a 2-pin package, make sure that the band end of the Zener is on the same trace as the + end of the 3.3 uF electrolytic capacitor.

The interior of a Series 1 Early Production equalizer, showing replaced componnets including capacitors and semiconductors.

Zoom in on this “after” photo where the semiconductors and capacitors were replaced for a view of how it might look when you’re done. (I was doing some testing so replacing components only a few at a time in this one; the semiconductors were all replaced but most resistors are still original in that photo.)

Series 1 Mass Production

The mass-production version is much cleaner:

An inside view of a Series I Mass Production model showing original unreplaced components.

The schematic for the Series I mass production model taken from the service manual. — Bose 901 Series 1 Mass Production Schematic – Click to Zoom In

One change is that to access the bottom side of the board on the mass-production version, you have to de-solder the two output jacks. Otherwise, it’s a much more mature design with improved power filtering, similified equalizer topology, and no Zener diodes. A few components were changed out to be slightly higher (e.g., 470 Ohm became 510 Ohm) as well.

Starting with the Series I, you can often get away with doing a bit less – although I recommend doing the whole thing while you’re in there.

All electrolytic capacitors need to be replaced.
- 500 uF x 2 (replace with 470 uF 35V) main power supply filter capacitors
- 100 uF x 7 (replace with 100 uF 35V) small power supply filter capacitors
- 5 uF x 4 (replace with 4.7 uF 35V) output & feedback loop capacitors

Now, you might get lucky and that’s it. Depending on the timeline for your particular model, you might have some more work to do. For starters, the dark red paper-mylar capacitors (like shown in the above photo) often go bad – you can even see how they start to discolor in the center. These need replaced at a minimum.

A closeup of a mass production Series 1 circuit board, with a circle highlighting a set of three red paper-mylar capacitors which have visible discoloration in the center indicating that they have failed and need to be replaced.

There were a variety of iterations on components (and also some variability in what was used depending on where they were manufactured). Red ones should always be considered bad, and that was especially unlucky in this model in which every single one of the capacitors was a subject-to-failure model.

Towards the end of the production run, you might find all orange caps (not red), or MMK or WIMA square capacitors. These are generally reliable. You can certainly replace them – and I usually do for good measure and for closer matching – but they’re usually fine to leave.

Transistors are less likely to be bad on the Mass Production model than the Early Production, but they are still a bit of a gamble. On some of the earliest Mass Production units, they’re still using the failure prone pencil-eraser packaging instead of the modern TO-92 packaging like you saw on the Early Production version, so definitely replace those. Otherwise, they’re usually fine, but do turn up bad from time to time. You’ll find this out after power up if one channel is dead.

Here’s the parts list and links to buy at Mouser for a Bose 901 Series I Mass Production model equalizer:

An interior view of a Series 1 mass production equalizer with all components replaced, arranged neatly in rows.

If you have (or had) a 240V model, there will be a 10K 5W resistor on/near the power switch to do the voltage conversion. If it’s missing, or jumped over, it’s 120V. It’s a different shape sometimes.

A view of the rear of the power switch inside the equalizer, showing a 10K Ohm 5W resistor used to run the unit on 240V power.

A different view of the rear of the power switch inside the equalizer, showing a different 10K Ohm 5W resistor used to run the unit on 240V power.

A not-uncommon problem with these voltage-converted or overseas models is hooking up to the wrong voltage, especially if the voltage stickers aren’t swapped over. Hooking up the US 120V configuration to 240V mains will cause a real problem and burn out your transformer very quickly; it might also fry some of your transistors and burst capacitors as the secondary voltage would also be double.

If you find yourself in this situation, the Tamura 3FD-336 (Microtran PSD3-36) is a good replacement. The voltages are correct out of the box. You’ll need to drill a couple of new holes and use a couple of jumper wires – it uses a dual primary and dual secondary configuration. Make sure to read the datasheet. (If you’re handy with Ohm’s Law, you could use a different transformer and adjust the values of R20/R21 to get what you need, too.)

A picture of the circuit board with the power transformer removed, showing large highly visible burn marks where the board was damaged and the transformer destroyed by running it on 240V power when it should have been run on 120V power.

In contrast, if you hook a 240V equalizer up to US mains, it’ll just…not work properly, if at all.

When you’re all done, the frequency response curve is pretty striking to see. It’s really doing a lot of work. It’s the same for both the Early and Mass-Production versions.

A frequency response curve of the Series I equalizer generated using an Audio Precision analyzer, with large peaks up to 20 dB centered about 30 Hz, and 14 dB at 20 kHz.

Bose 901 Series II Active Equalizer

The Bose 901 Series II Active Equalizer is substantially similar. The speakers are the same with only some minor visual changes; the equalizer itself removes a handful of components inside and removes the power switch (so you’ll want to connect it to a switched power strip or your system’s switched power outlet if there’s one available.) They have the same particle board and contact paper cases.

A front view of a Series 2 equalizer on the bench. Unlike a Series 1 equalizer, this one has no power switch and is always on when plugged in.

A rear view of a Series 2 equalizer on the bench showing a slightly different arrangement of input and output jacks.

Like the Series I, the Series II also comes in a 240V model, which uses the same 10K 5W resistor on the input power as described earlier in this article. Inside, there are a few components removed, and one change to the power supply: instead of 2 and 7, it’s 3 and 6 capacitors. A couple resistor values are swapped as well. Otherwise, it’s all the same stuff.

The schematic for the Series II is here. Click to zoom in. Interestingly enough, there’s a typo – the 3rd power supply filter capcaitor is listed as 100 uF on the schematic, when every single model I’ve ever seen of the Series II had another 500 uF cap in that spot.

Bose 901 Series 2 Active Equalizer Schematic – Click to Zoom In

An interior view of the Series 2 equalizer showing original components.

An interior view of a Series 2 equalizer with all components replaced in neat rows.

Here’s the parts list for overhauling a Series II.

Now, one unusual thing you’ll potentially come across is really different looking. Some of the earlier Series II models actually use a Series I circuit board with some jumper wires, with a few components ommitted or attached directly to the Contour control.

An interior view of a Series 2 equalizer built from a modified Series 1 circuit board, with some components replaced, illustrating an unusual and undocumented factory revision they made to use up old boards before switching fully to new production.

The power supply segment is the same as the Series I, but even though the board layout is the same, some of the values are different, not populated, or are mounted directly to the contour switch. These aren’t super uncommon – I probably saw a couple dozen in this configuration – but are less common than the Series I Early Production version. Almost certainly in part due to the age difference.

If you’re going to do an overhaul, the transistors and diodes are the same as the Series 1 Mass Production (above), and so are the electrolytic capacitors, but it’ll use the resistors from the Series II above.

Regardless of which board yours has, both versions of the Series II produce the same equalizer curve, which is almost identical to the Series I. You can use either interchangeably and it’s just fine. (Apologies for the weird scaling on this one.)

A frequency response curve of the Series 2 equalizer generated using an Audio Precision analyzer showing similar peaks as the Series 1, centered around 30 Hz and 15 kHz this time.

Bose 800 Professional PA System

The Bose 800 PA system is the live-sound version of the 901. As the number might imply, it uses only 8 drivers instead of 9 all on the angled side, and it’s designed to face into the crowd like a more traditional loudspeaker.

A decorative arrangement of a set of Bose 800 Professional PA speakers, with road cases, and one grille removed to reveal the 8 drivers on the front with blue paper surrounds.

The speakers themselves use 1/4″ jacks with a passthru, and are fused for protection and coated with tolex like road gear often is. Like the 901s, due to the nature of the array of small drivers, they need to be used with the Bose 800 Active Equalizer to get the proper sound quality. The 800 offered Series I and Series II versions as well.

Bose 800 Active Equalizer

The 800 Active Equalizer came in a Series I and II version, based on the 901 chassis. I haven’t been able to find any service manuals or schematics for these, but based on the information above, you should be good enough.

A badly banged up earlier 800 Active Equalizer, similar to a 901 Series 1, covered in duct tape and with spray painted markings on top. — 800 Series 1 (power switch)

An 800 equalizer based on the Series 2 platform, in much nicer shape than the previous. — 800 Series 2 (no power switch)

These often get pretty banged up following a life on the road. The Series I has a switch; the Series I lacks one.

A rear view, common to both types of the 800 equalizer, showing quarter inch input and output jacks common on professional audio systems.

Both have 1/4″ jack systems, and there’s no tape loop on these. They came in 120V and 240V versions which also used the same dropping resistor system as on the 901s. There were a few production variations; I’ve found Series I systems with Series II boards inside, and vice-versa.

If I had to guess, without actually researching, I’d say the 800 probably came out towards the end of the 901 Series 1 lifetime, and was refreshed into the 800 Series 2 somewhat after the 901 Series II was released, so they were using up old cases with the newer common circuit board.

An interior view of an 800 Series 1 equalizer showing original components. — 800 Series 1 with a Series 1 board

An interior view of an 800 Series 2 equalizer showing original components. — 800 Series 1 with a Series 2 board

I’ve also run into a few which were either modified or came from the factory with a 600 Ohm output impedance:

An 800 series 2 equalizer with all components replaced. This unit has two additional resistors connected to the output jacks.

The 800s came on the scene a bit later than the 901s. You can generally get away with replacing only the electrolytic capacitors and any of the red paper-mylar capacitors on these models. While I did often replace semiconductors by customer request at the time to improve channel matching, I don’t think I ever ran into an 800 with defective transistors or diodes.

The equalizer curve is much the same. You could get away with using 800 or 901 equalizers interchangeably.

A frequency response plot of the 800 equalizer produced using an Audio Precision analyzer showing peaks at 40 Hz and 12 kHz. Slightly different, but close enough if you only had a 901 and wanted to make it work.

Mods & Bodges

Now, with any popular system that’s been in service for a while, these things often had repairs of differing quality. Some came in with replaced electrolytic capacitors only, but film parts or semiconductors had failed since:

A 901 Series 1 early production equalizer with a handful of electrolytic capacitors only replaced but the rest of the original components, not following a best practice for repair.

A Series II equalizer with a very badly performed repair, with one electrolytic capacitor tacked in on top and large blobs of solder visible.

Or sometimes you’d get replaced jacks or a replaced power switch:

A Series 1 equalizer with a large red and black power switch in place of the original clear plastic switch, with an obviously different and clashing visual style.

I’m not entirely sure what this mod was trying to accomplish, and it looked pretty dodgy.

An interior view of a Series 2 equalizer with a modification to the power transformer; it's off-center (possibly from a Series 3) and held on by one screw, with mystery diodes connected to an unidentified wire and the unit's ground plane.

I saw a few that had gone through another well-known shop back at that time, with a ton of expensive upgrades, but the electrolytic capacitors in the power supply had failed. Could be bad luck, the workmanship was good. This shop had a different perspective than I did which was always interesting to see. Lots of room for different opinions in the vintage audio world.

A Series 1 equalizer with significant work done previously, including an all new power transformer, electrolytic capacitors, and expensive film capacitors installed.

Finally, I saw one absolutely bonkers homebrew clone of the Early Production Series I:

Front panel of a homebrew equalizer with all of the same controls as a Series 1, but of a pretty rough looking design.

The rough rear panel of the homebrew Series 1 equalizer showing input and output jacks and a few miscellaneous screws.

The interior of the homebrew Series 1 equalizer showing a partial view of two out of three circuit boards on their original components.

At least I think it’s homebrew, although those are some nice looking circuit boards. I did fix it, and it did work!

Postscript

No, I am not accepting repairs currently, but I hope this will help you with yours.

Mouser parts were correct and current as of publishing (June 2026). They may change over time. And probably will: when I started with these equalizers in 2012, I was using Xicon 1% metal film resistors, and Nichicon axial electrolytic and film capacitors. By 2021 when I stopped doing this as a business, Nichicon axial electrolytic caps were unavailable. Now, their film caps are out as well. I’ve selected good quality replacement parts which I’d be happy if any shop used in my repairs.

Leave a comment if you have a question, but I might not be able to give you individualized advice.

Posted in Audio, Bose, Collections, Resources | Tagged 800, 901, Active Equalizer, Bose, Bose Active Equalizer, Bose Equalizer, Computers, diy, electronics, philosophy, series I, series II, stereo equalizer, Technology, vintage stereo | 3 Comments

The Speaker Spotter — June 10, 2026

Posted on June 10, 2026 by retrovoltage

A recurring feature curating interesting speakers for sale on Craigslist from around the Pacific Northwest. Links to Craigslist postings might go down at any time if they’re sold or pulled from sale. This one was delayed while I was traveling, so we might skip the Friday 6/12 issue to give folks time to list new and interesting things for sale.

IMF TLS 50-II speakers loudspeakers; pair

$775 · SE Portland (Portland)

British-made from the late 1970s/early 80s, the IMF TLS 50-II is a transmission line loudspeaker — a relatively rare bass-loading design that uses a long, damped internal duct to absorb and release woofer back-wave energy rather than trapping it in a sealed box. These used KEF drivers and sold for over $1,500 new. Really interesting design – I’m not super familiar with transmission line speakers, but I’m a fan of KEF.

Paradigm 40 Active

$1,500 · Hillsboro (Portland)

The Paradigm Active 40 is a self-powered studio-reference speaker from Paradigm’s acclaimed Active series of the late 1990s — each cabinet contains its own tri-amplified electronics with individual amplifiers for tweeter, midrange, and woofer, eliminating passive crossover losses entirely. Original boxes included is a bonus for safe transport; at $1,500 these are a significant but worthwhile ask for powered monitors of this caliber.

McIntosh ML-1C speakers with stands

$350 · Albany (Corvallis)

McIntosh is better known for its amplifiers and preamplifiers, but the ML-1C is a solid example of the company’s speaker division — a 3-way acoustic suspension design from the 1970s built with the same attention to build quality the brand is famous for. Re-foamed with stands included at $350, these are a collectible piece of McIntosh history at a very approachable price. Pair them with an MQ-101 equalizer and you’ve got a fantastic system!

Acoustic Research 3a Speakers

$600 · Boise

The AR-3a was one of the most important loudspeakers ever made — introduced in 1967, it helped establish acoustic suspension (sealed box) design as an audiophile standard and remained a benchmark for bass accuracy and imaging for over a decade. Fully functional at $600 in Boise, this is a rare opportunity to own a foundational piece of hi-fi history in a cute and unassuming package.

Klipsch KLF-30 Tower Speakers

$1,900 · Boise

The KLF-30 is one of the largest and most powerful speakers from Klipsch’s KLF (Klipsch Legend Forte) line of the mid-1990s, featuring a 12-inch woofer and Klipsch’s signature horn-loaded midrange and tweeter for high efficiency and room-filling sound. All-original with no replaced drivers and tight cabinets — a known weak point on some production runs — this pair in Boise at $1,900 is a compelling find for Heritage-adjacent Klipsch collectors. I used to own a set of these some years ago, and they’re excellent.

Vintage Nelson Reed 8-04/BI Tower Speakers (1 Working, 1 For Repair)

$1,350 · Bellingham

Nelson Reed was a small, boutique American speaker manufacturer from the 1970s-80s that built large, highly efficient horn-assisted tower speakers largely unknown outside of audiophile circles — making any clean pair a genuine rarity. At 47 inches tall, these imposing towers are listed as one working and one needing fuse/repair work; at $1,350 there is a project element, but for the right restorer these could be a worthwhile score.

Sansui SP L700 Speakers

$350 · Port Townsend (Olympic)

The Sansui SP-L700 (sold as the SP-G200 in Japan) represents one of Sansui’s most ambitious home speaker designs — a large, furniture-grade enclosure with distinctive Mid Century Modern styling and a reputation as one of the best speakers the brand produced. This refinished pair in Port Townsend has had its foam replaced and grilles are intact; the missing acoustic lens covers are a minor cosmetic issue on an otherwise beautiful and hard-to-find speaker at $350.

KLIPSCH KSF 8.5 Floor Speakers

$250 · Tacoma (Seattle)

The Klipsch KSF 8.5 is a floorstanding speaker from Klipsch’s mid-1990s KSF series, featuring a horn-loaded tweeter and an 8-inch woofer — a step down from the Heritage line but still delivering Klipsch’s characteristic high efficiency and dynamic punch. At $250 for a pair in working condition in Tacoma, these represent solid value for a vintage Klipsch floor-stander. Sounds great for mid/high, but you’ll want a sub for the low end. I’d say these are better as a part of a home theater system than a necessarily a listening system.

JBL 2600 Bookshelf Speakers

$80 · Cully (Portland)

The JBL 2600 is a compact two-way bookshelf speaker from JBL’s consumer lineup of the 1980s, notable for using the same titanium-dome tweeter technology found in JBL’s professional studio monitors of the era. Well cared for and fully working in Portland at $80, these are an affordable entry point into the JBL vintage ecosystem.

NHT Audio VT-1A Tower Speakers, Gloss Black – Excellent Cond

$375 · Meridian (Boise)

NHT (Now Hear This) was a California-based audiophile brand of the 1990s known for its sealed, time-aligned designs and glossy lacquer finishes — the VT-1A is a slim tower that punches above its weight in imaging and soundstage width. USA-made and in excellent condition with the original gloss black finish intact, this Boise pair at $375 is a solid buy for fans of 1990s American high-end audio. “High end speakers from companies that are less focused on audio” is always an interesting genre and sometimes you get a real gem. Not sure about these, but they’re certainly different.

Posted in Uncategorized | Leave a comment

Upcoming Projects for 2026

Posted on June 2, 2026 by retrovoltage

Having had a chance to unpack some of my shop from storage and settle in to the new space, I’ve got an idea of what projects I’ll be working on myself in between projects with my shop partner.

Bose Active Equalizers

Of course, since I used to be a top service provider for these, I have a whole bunch in stock which I’ll need to get through. I picked these up as parts units whenever I could find one for a steal, which was often due to cosmetics. The earliest 901 Series I cases were made of solid wood and hold up pretty well, but past the first ~10,000 units produced switched to particle board with a contact veneer until the Series III was released. Those get to be in pretty bad shape. I wonder if my partner can reproduce them on the wood shop side of the house.

With four Series I, a Series II, two Series IV, and a pair of 800 Series I equalizers (the same as a 901 Series I except with 1/4″ connetcors and none of the tone/tape controls) this should keep me busy for a little bit.

A 901-I/II has about 90 components to replace for a full makeover and takes about 4 hours from start to finish. The 800 equalizers have about 60 components and take maybe 2 and a half hours. Bose switched to a different design for Series III, and the Series IV only has a handful of capacitors in the power supply and signal chain. Some models used LF353N op-amp chips which were subject to a service bulletin and need to be replaced with TL072s. (Interestingly enough, some of these seem to be fitted with chip sockets from the factory and some have soldered chips, so sometimes it’s a really easy swap.)

This will keep me for maybe 10 sessions in the shop. I don’t make it in every week, and when I do, it’s usually for 3-5 hours.

1934 HMV 444

I’ve also got a His Master’s Voice Model 444 radio which I added to my collection more than 15 years ago. (I have the blog post to prove it!) At the time, I paid $60 (plus driving two hours each way) for the radio which had been restored by a long-retired Master Carpenter who found stuff locally at garage sales and gave it away for the same price he paid after re-doing the wood.

It’s not a big radio – maybe up to my waist – and it was only a 5 tube radio so nothing especially interesting electrically. But this is a 220V UK radio, and the truly striking art deco styling sets it apart. The schematic is drawn very differently from U.S. conventions but knowing the general theory, it’s pretty easy to follow. Should be a fun project, although it’ll take a few sessions of detailed measurement and tedious component replacement to get it across the finish line.

Sony TA-5650 VFET Stereo Receiver

I ended up with this Sony TA-5650 VFET receiver tin 2019 or 2020. I’ve done a good handful of these in the past, including several for multiple Grammy-nominated record producer Kavi Alexander of Water Lily Acoustics. This one is from an original owner, even. They’re really special, and deceptively simple, except for one detail.

These are from an era of heavy experimentation in semiconductor technology, the early-mid 1970s, and ended up using output transistors (FETs) which are a drastically different design and topoogy than anything else in common use before or after. They all need to be perfectly matched within the same rank as each other, and some traditional service best-practices (like using a variac to slowly bring an amp online for the first time after service) are guaranteed to destroy the output finals if used with this particilar piece of kit.

If you end up in that situation…good luck finding those semiconductors anywhere else ever again. There are some mods floating around to let you use a more traditional output device, but it’s a heavy rework job, and you lose some of the character that way. (These also use a small-signal VFET in the preamp chain for some reason.)

Adding to the mystery, when initially inspecting this one on intake, I found that it looks like there’s a factory revision to the final circuit board which wasn’t documented in the service manual. There are a few pieces of service errata – a couple of component swaps, changed bias values – but this one looked to have a few extra components and some different values installed. I didn’t look into it further to know whether it’s an early production or a late prodution model. Should be interesting.

I also need to adjust one of my two Audio Precision System One analyzers (and probably replace a few components in the power supply), so realistically, this set of projects will take me the rest of the year. I’ll post about it here as I go.

Posted in Uncategorized | Tagged Bose, cw, electronics, hmv 444, radio, Sony TA-5650, stereo, Technology, vintage stereo | 1 Comment

The Speaker Spotter — May 29, 2026

Posted on May 29, 2026 by retrovoltage

A recurring feature curating interesting speakers for sale on Craigslist from around the Pacific Northwest. Links to Craigslist postings might go down at any time if they’re sold or pulled from sale. This week’s report is KEF heavy, with a dash of Sansui, and a few randoms thrown in. Happy listening!

Revel Performa3 M106 (Bookshelf Speakers)

$1,099 · Lynnwood (Seattle)

The Revel Performa3 M106 is a serious audiophile bookshelf from Harman’s flagship Revel line, featuring a 1″ ceramic dome tweeter and 6.5″ aluminum cone woofer tuned for reference-level accuracy. These would be the base of a solid desktop system, or even potentially as surrounds for a home theater.

Klipsch Quartet Speakers Oak Color

$700 · Tacoma (Seattle)

The Klipsch Quartet is a full-size Heritage-adjacent floor stander from the late 1980s, built on Klipsch’s classic horn-loaded philosophy for high efficiency and dynamic punch. At $700 in Tacoma these show normal cosmetic wear but are described as working well. I’d love to own a set of these myself.

Sonus Faber Venere 1.5 Speakers and Stands

$700 · Tacoma (Seattle)

Sonus Faber’s Venere 1.5 is a slim two-way standmount from the Italian maker’s mid-tier Venere line, prized for its warm, musical presentation and refined cabinet work. This Tacoma pair comes with matching stands in excellent condition, they’re often beat up or missing for some reason.

Magnepan Speakers

$75 · Vancouver (Portland)

The Magnepan SMGA is a quasi-ribbon planar speaker from the early 1990s, offering the wide, seamless soundstage that Magnepan is famous for at a size that fits most rooms. This Vancouver pair is sold as a project — one panel has the common delamination issue — but for a capable restorer the price is right. A local stereo consignment shop near me has 3 or 4 pairs of these at any given time and they sound pretty good (if not with a ton of bass) but need a really big power amplifier to drive them properly.

KEF Floorstanding Speakers (103/4)

$350 · Lynnwood (Seattle)

The KEF 103/4 is a respected floorstanding entry from KEF’s Reference Series of the mid-1980s, equipped with KEF’s B200 bass unit and T27 tweeter in a carefully tuned cabinet for smooth, wide-dispersion sound. This Lynnwood pair is a strong pickup for anyone wanting classic British hi-fi engineering at a fraction of its original price. I personally like KEF quite a bit and use their speakers if I do a resto-mod upgrade for a vintage radio because of the coaxial drivers. (You’re not doing that with a floorstasnding unit, though!)

KEF C40 Floorstanding Speakers

$150 · Lynnwood (Seattle)

More KEF, these KEF C40 are a compact two-way bookshelf from KEF’s C Series, delivering the brand’s characteristically accurate midrange in a package suited to smaller rooms or desktop listening. Priced at $150 in Lynnwood, these represent genuine KEF quality at an accessible entry-level price.

Dahlquist M905 Speakers

$150 · Mountlake Terrace (Seattle)

Dahlquist is a celebrated American speaker brand best known for the DQ-10 time-coherent design that defined audiophile listening in the 1970s; the M905 is a later bookshelf that carries that legacy of careful voicing and imaging. The seller in Mountlake Terrace is offering demos, which is always a good sign. This isn’t the big, flat, open-baffle one you usually see for sale but it looks interesting, especially with the metal? metalized? woofers.

Vintage Kef Speakers

$250 · Albany (Corvallis)

Lots of KEF today. The KEF Model 103/3 Reference is a sealed three-way loudspeaker from 1986 that originally retailed for $1,500 a pair — a genuinely serious box from KEF’s peak Reference period. This Albany pair is in unspecified condition but that’s a solid price at $250 and they look intact and set up to listen, so it’s probably worth it.

Vintage Sansui Stereo Collection – AU-717, TU-919, AU-317, Turntable, Speakers

$2,500 · Bonners ferry (Spokane)

This is a rare single-owner collection of vintage Sansui gear: two integrated amplifiers (AU-717 and AU-317), the highly regarded TU-919 tuner, an FR-D3 turntable, an SE-5 equalizer, and speakers — all from a builder that defined the “Golden Age” of Japanese hi-fi. At $2,500 for the lot from Bonners Ferry, it’s the kind of collection that rarely surfaces intact. (Everything is certainly going to need restored, but this is a whole collection. I’d try and snag it for $1750-2000, personally.)

Infinity SM-85 Studio Monitor Bookshelf Speakers

$275 · Bothell West (Seattle)

The Infinity SM-85 is a studio-monitor-grade bookshelf from the 1980s, built around Infinity’s Poly-Cell™ tweeter and featuring a notably high 98 dB sensitivity that makes it easy to drive. This Bothell West pair tests out well and at $275 is a sensible buy for anyone wanting analytical, high-efficiency monitoring. Overall, a good little speaker.

Micro Acoustics MA Pro-1 Speakers

$250 · Happy Valley (Portland)

Micro Acoustics was a short-lived but innovative American speaker company whose electret-based tweeter array drew a patent lawsuit from Bose — making these speakers a genuine piece of hi-fi history. The MA Pro-1 is the top of the Pro Series line, and this Happy Valley pair are described as very rare and hard to find. Really unusual looking.

Sansui SP L700 Speakers

$450 · Port Townsend (Olympic)

The Sansui SP-L700 (sold in Japan as the SP-G200) is considered one of Sansui’s finest speaker achievements, featuring furniture-quality cabinetry with a teak veneer and a four-driver array tuned for deep, musical bass. This Port Townsend pair is described as solidly built and in excellent shape — a genuinely uncommon find in the Pacific Northwest. If only it had the beautiful lattice grillework to go with it you find on the more recognizable Sansui models!

Posted in Uncategorized | Leave a comment

DBX SFC-10 Soundfield Imaging Controller Repair

Posted on May 23, 2026 by retrovoltage

I’ve had this DBX SFC-10 Soundfield Imaging Controller in my stash for a while, and figured I’d ease into repair work again with a relatively easy project. I’ve always been interested in speakers which use an active equalizer – the McIntosh MQ101, the Bose 800/901 series, there’s a rare Electro-Voice, and there’s the DBX SFX-10 speakers.

These were nice speakers back in the day, but for whatever reason aren’t especially collectible and must not have sold very well because they’re pretty uncommon to come across. They use an omnidirectional design. They’ve got 2 x 10″ woofers, a mid, and a tweeter array each and are designed to throw sound in all directions while preserving imaging. Somewhat similar in that regard to the Bose 801 Direct/Reflecting system. You can often find these for a pretty low price, a few hundred dollars, but as with most other systems of this type the controller is needed for them to sound any good, and it tends to go missing.

Front view of the DBX SFC-10 Soundfield Imaging Controller on the work bench.

DBX equalizer rear view showing connections; input/output on the left and tape loop connections on the right

A top-down interior view of the upper side of the circuit board inside the EQ

It’s a surprisingly complex little device in there, with a date code showing it was manufactured in mid-1985. There’s 8 op-amps, a handful of transistors, and a hefty regulated bipolar power supply. The board is 2 layers, with plated via – some engineer must have had a big budget when designing it.

A top-down view of the bottom side of the board inside the equalizer

There was evidence of a previous repair at one point. Not entirely surprising.

A close-up view of two electrolytic capacitors on the circuit board, one is newer than the other showing the evidence of repair.

I did an initial power-up test just to see the current condition, and unsurprisingly, it wasn’t working properly. Bad capacitors, per usual.

A close up view of the power supply section of the equalizer, with the two main capacitors removed, revealing a ring of fluid leakage beneath one confirming evidence of the failure.

A view of the bottom side of the removed capacitor from the previous image, showing that the plastic sheath is crinkled slightly - evidence of leakage producing heat - and there is a crust of leaked fluid around the edges.

Replacing them all with nice new Nichicon caps from my existing stock took about 20 minutes. While I had the board apart, I also cleaned the equalizer controls.

An angled view of the equalizer circuit board, showing several new Nichicon capacitors have been installed.

Okay, great. Time to see what it does! My AP ATS-2 died the final death some time ago, but when I came back to the hobby I scored a great deal on a System One, which is the one I started with many years ago so it’s like an old friend, and it’s exactly what I needed to check out what this controller does.

The equalizer hooked up to the Audio Precision System One analyzer, showing a complex graph of overlapping frequency response curves on the attached PC display.

Let’s take a closer look:

A close-up of the PC screen readout showing six curves plotted on a single display, with labels below to differentiate them. The equalizer has a large bass peak around 30 Hz, a dip at 50Hz, a slight peak at about 100 Hz, then declines to a low point around 1000 Hz, before steadily climbing up to around 20 kHz.

One thing that took me some time to figure out was the “ambience” control on the front. It never seemed to do anything that I could see with the analyzer. No matter the control’s position, there were no meaningful changes in the frequency response, phase, or distortion. It took a trip to the manual to figure out what was going on:

Well, that explains it. With the equalizer hooked up to the AP, both channels were getting an identical signal, so L-R = 0, and nothing at all is modified in the signal. You can download the full manual here, originally from HifiEngine, but if you don’t already have an account over there it can be difficult to get one.

All in all, this was a quick and easy project, and a great way to ease back into electronics repair.

Posted in Uncategorized | Leave a comment

The Speaker Spotter — May 22, 2026

Posted on May 22, 2026 by retrovoltage

Pair of Vintage Bose StudioCraft Tower Speakers

$200 · Seattle (Seattle)

Bose’s StudioCraft towers are a late-1980s footnote in Bose history, employing the brand’s multi-driver psychoacoustic approach in a floor-standing format that is far less common than the famous 901. This Lacey pair needs some work (two drivers may require reconing) but offers a fun restoration project or parts source at $200. I’m almost positive I’ve seen these listed for literally years, coming way down in price, and they’re getting to be worth it for some unusual Bose. I’d probably take 601s or even 501s if I wanted floor-standing Bose, though.

Bowers and Wilkins B&W 805 Nautilus Stereo Speakers

$1,475 · Spokane (Spokane)

The B&W 805 Nautilus is one of the most celebrated standmount monitors ever made, featuring B&W’s iconic Nautilus tube tweeter loaded from behind to virtually eliminate rear reflection distortion. This Spokane pair includes upgraded aluminum phase plugs and is in excellent condition at $1,475 — a significant step below the original ~$4,000 MSRP.

JBL 3 MKII Powered Studio Monitors + Focusrite Scarlett Solo

$180 · Portland (Portland)

The JBL 305P MkII borrows boundary EQ and image control waveguide technology from JBL’s high-end studio gear, making it one of the best values in powered nearfield monitors. This Portland listing bundles a pair with a Focusrite Scarlett Solo audio interface — everything needed for a desktop studio or nearfield listening setup — at $180 for the lot.

Klipsch KLF retro tower speakers

$750 · Boise (Boise)

The Klipsch KLF series are horn-loaded towers from the 1990s that bridge the gap between the classic Heritage line and modern designs, rated at a room-filling 101 dB/W/m sensitivity. This black-satin pair near Boise is listed at $750 — dynamic, punchy, and easy to drive with even modest amplification.

Bose 901 speakers

$225 · Seattle (Seattle)

The Bose 901 is arguably the most audacious speaker design of the 20th century, using eight rear-firing drivers to bounce 89% of the sound off the walls in Amar Bose’s recreation of a live concert environment. This Tacoma pair includes the required equalizer and all 18 drivers are confirmed working — a complete, functional system at $225. The 901 Series 1 and 2, like these, use rubber surrounds which don’t degrade so these should last a very long time.

Vintage KLH Model 17 Speakers

$175 · Pullman (Pullman)

KLH was co-founded by Henry Kloss, the acoustic genius behind the Large Advent and the AR bookshelf speaker, and the Model 17 is a compact two-way that showcases his talent for natural, musical sound in a small cabinet. This carefully refreshed pair in Moscow, ID has new capacitors and treated surrounds, and the seller will demonstrate on a receiver before purchase at $175.

Sansui vintage speakers

$200 · Spokane (Spokane)

The Sansui SP-1500 is a large 3-way floor stander from Sansui’s golden era of the early 1970s, featuring a 12-inch woofer and the characteristically warm, full sound that pairs beautifully with vintage receivers of the period. A solid opportunity in Spokane at $200 OBO for anyone building a vintage Japanese system.

Wharfedale Obsidian Tower Speakers

$600 · Olympic (Olympic)

Wharfedale, founded in Yorkshire in 1932, is one of the oldest hi-fi brands in continuous production, and the Obsidian Tower is a 3-way reflex design with a 1-inch silk dome tweeter, twin 5.25-inch mids, and an 8-inch side-firing woofer that delivers classically voiced British hi-fi. Available near Sequim, WA for $600.

Cerwin Vega AT-12 speaker

$60 · Portland (Portland)

The Cerwin-Vega AT-12 is a 3-way tower known for high sensitivity and the ability to play genuinely loud without straining — a CV hallmark. This single cabinet came from an estate sale in Gladstone, OR and is offered with a money-back guarantee at $60, ideal for someone hunting a matching partner or looking for a robust bass cabinet.

Posted in Uncategorized | Leave a comment

The Speaker Spotter — May 15, 2026

Posted on May 15, 2026 by retrovoltage

JBL L65 “Jubal” — $1,800 (Kennewick, WA)

JBL’s legendary L65 “Jubal” from the mid-1970s is one of the company’s most coveted vintage offerings, pairing a 12-inch woofer with a midrange and titanium tweeter. This all-original pair is in good condition with minor cosmetic damage; the seller notes they’re best suited for larger rooms with acoustic treatment — a hallmark of these high-sensitivity, expressive three-way speakers.

Dahlquist DQ20i — $700 (College Place, WA)

The Dahlquist DQ20i is the final design from Jon Dahlquist, featuring an innovative open-baffle midrange/tweeter array that produces a famously wide, airy soundstage. This very-good-condition pair originally sold for ~$2,000; buyers should note the woofer foam surrounds may need re-foaming after 30+ years, but at $700 the price-to-performance ratio is exceptional for a speaker of this pedigree.

Altec 416A Woofers (Pair) — $600 (Kennewick, WA)

The Altec 416A is one of the most respected 15-inch woofers ever made, prized for its legendary low-frequency extension and efficiency in horn-loaded and vented enclosures — the same driver found in countless professional PA systems and high-end DIY builds. This pair is in very good condition with one professionally re-coned in Portland, making them an excellent foundation for a serious speaker project.

1978 Klipsch La Scala (Single) — $1,000 (Shelton, WA)

A 1978 Klipsch La Scala in birch — one of Paul Klipsch’s cornerstone Heritage horn-loaded designs — offered here as a single speaker in excellent condition with original box and paperwork. At 104 dB/W/m sensitivity, these folded-horn three-way cabinets are extraordinarily efficient and instantly recognizable by their large, boxy footprint and live-sounding presentation. A rare piece of PNW audio history.

Speakerlab Three’s (Pair) — $160 (Edmonds, WA)

Speakerlab was a beloved Seattle-based loudspeaker company that built a devoted following in the 1970s–80s offering audiophile-grade kits and finished speakers direct to consumers. These floor-standing Threes are a working pair in excellent condition — all drivers and cones intact — originally retailing for $1,200–$1,500. A genuine piece of Pacific Northwest audio heritage at a very friendly price.

ADS B7 Bookshelf Speakers (Pair) — $150 (Sequim, WA)

ADS (Analog and Digital Systems) earned a strong reputation in the 1980s for exceptionally accurate, neutral-sounding monitors favored by home audiophiles and recording engineers alike. This pair of B7 bookshelf speakers is in excellent condition with all drivers intact; the seller will throw in a third B7 for just $50 more — handy for a spare or parts. Delivery is also available.

Vintage ESS AMT 1b Heil Air-Motion Transformer Speakers — $580 (Tigard, OR)

The ESS AMT 1b is one of the most technically fascinating speakers of its era, featuring Dr. Oskar Heil’s Air-Motion Transformer — a folded pleated diaphragm that squeezes air sideways rather than pistoning it forward, producing exceptionally fast and detailed high-frequency reproduction. These large floor-standers (16.5″ × 16.5″ × 35.5″) are in good shape and are a genuinely rare find for collectors of unconventional transducer technology.

Polk Audio SDA 1 Stereo Dimensional Speakers — $975 (Vancouver, WA)

Polk’s SDA 1 pioneered Stereo Dimensional Array technology, using a proprietary interconnect cable between the two towers to cancel inter-aural crosstalk and create a dramatically expanded, three-dimensional soundstage. This mint-condition pair includes the interconnect cable (which sells for $120 alone on eBay) and is rated for 50–500W amplifiers — an audiophile experience at a fair price for the technology involved.

Klipsch Cornwall Speakers — $3,000 (Vancouver, WA)

Early-1980s Klipsch Cornwalls from the original owner’s estate — these Heritage series three-way speakers use a direct-radiating woofer combined with mid-range and tweeter horns for the combination of efficiency and dynamic authority that made Klipsch legendary. Both speakers work perfectly and have been in the same family since new. The Cornwall remains one of the most sought-after Heritage designs for its ability to fill large rooms at whisper-quiet amplifier levels.

JBL 4430 Studio Monitors — $3,000 OBO (Spokane, WA)

The JBL 4430 is a professional Bi-Radial studio monitor used in major recording control rooms throughout the 1980s and 90s, featuring the legendary 2235H 15″ woofer, 2344 Bi-Radial horn, and original compression drivers — all intact and functional. The cabinets have been professionally re-veneered and left unfinished so the buyer can apply their preferred oil or stain. These are not typical consumer speakers; they are a serious find for a serious room.

Bowers & Wilkins DM601 Series 2 — $450 (South Hill/Spokane, WA)

Bowers and Wilkins DM601 Series 2 Speakers

The B&W 601 Series 2 is a well-regarded late-1990s bookshelf monitor featuring a 7-inch Kevlar bass/midrange driver and a Nautilus tube-loaded 1-inch alloy dome tweeter — technology trickled down from B&W’s flagship 800 series. This pair is in excellent condition with original grilles, Zu Audio jumpers, and original B&W boxes included, making it one of the more complete and ready-to-enjoy packages in this week’s roundup.

Posted in Uncategorized | Leave a comment

Find:

Search for:
About Me
- Shop Amazon with Retrovoltage
- Shop eBay with Retrovoltage
Blogs
Friends
Resources
- 6V6
- Active Equalizer
- AM
- amplifier
- Antique
- antique radio
- audiophile
- Bose
- Bose 901
- capacitor
- capacitor replacement
- cost engineering
- Craigslist
- diy
- eBay
- eico
- electronics
- Equalizer
- fried electronics
- GE
- General Electric
- grunow
- grunow 586
- grunow 589
- grunow chassis 5-U
- grunow radio restoration
- ham radio
- hf
- hi-fi
- HP
- Klipsch
- KN0CK
- LCD
- LF-116
- old radio
- oscilloscope
- philco
- photos
- power supply
- project
- projects
- radio
- radio retailing
- rca
- receiver
- repair
- replacement
- restoration
- RTLSDR
- SDR#
- Series 1
- shortwave
- soldering
- Sony
- Speakers
- speaker spotter
- stereo
- stromberg-carlson
- Technology
- teledial
- test equipment
- tube
- Tube Amp
- tube radio
- up-converter
- Upconverter
- vacuum tube
- vintage
- vintage ad
- vintage audio
- vintage radio
- vintage speakers
- vintage stereo
- Westinghouse
- zenith
Categories
Audio Bose Collections Commentary Computers DIY Electronics Gadgets Ham Radio Hardware Hi-Fi Ideas Internet Mailbag Music Photos Projects Radio Radios and Tubes Resources Speakers Stereo Technology Television Test Equipment Tips and Tricks Tools Toys Uncategorized Vintage
July 2026

S M T W T F S

1 2 3 4

5 6 7 8 9 10 11

12 13 14 15 16 17 18

19 20 21 22 23 24 25

26 27 28 29 30 31

« Jun
Meta

Part	Quantity
100 Ohm Resistor	1
510 Ohm Resistor	4
1K Ohm Resistor	8
1.5K Ohm Resistor	2
1.8K Ohm Resistor	2
2.2K Ohm Resistor	5
2.7K Ohm Resistor	2
3.9K Ohm Resistor	2
4.7K Ohm Resistor	2
10K Ohm Resistor	8
22K Ohm Resistor	4
39.2K Ohm Resistor	4
47K Ohm Resistor	4
56.2K Ohm Resistor	2
150K Ohm Resistor	2
274K Ohm Resistor	2
1M Ohm Resistor	2
2N5088 Transistor	10
1N4007 Rectifier Diode	2
0.015 uF Film Capacitor	6
0.047 uF Film Capacitor	2
0.1 uF Film Capacitor	4
4.7 uF Electrolytic Capacitor	4
100 uF Electrolytic Capacitor	7
470 uF Electrolytic Capacitor	2

Description	Quantity
100 Ohm Resistor	1
510 Ohm Resistor	6
1K Ohm Resistor	6
2.2K Ohm Resistor	5
2.7K Ohm Resistor	2
3.6K Ohm Resistor	2
3.9K Ohm Resistor	2
5.6K Ohm Resistor	2
10K Ohm Resistor	8
13K Ohm Resistor	2
22K Ohm Resistor	6
39.2K Ohm Resistor	4
47K Ohm Resistor	4
56.2K Ohm Resistor	2
150K Ohm Resistor	2
274K Ohm Resistor	2
2N5088 Transistor	10
1N4007 Rectifier Diode	2
470 uF Electrolytic Capacitor	3
100 uF Electrolytic Capacitor	6
4.7 uF Electrolytic Capacitor	4
0.015 uF Film Capacitor	6
0.1 uF Film Capacitor	4

Table of Contents

Why replace capacitors at all?

Electrolytic Capacitor Basics

Axial vs. Radial Lead Electrolytic Capacitors

Snap-In and Screw Terminal Electrolytic Capacitors

Polarized vs. Bi-Polar / Non-Polar Electrolytic Capacitors

Brands

Searching for Radial Aluminum Electrolytic Capacitors

Capacitance

Voltage

Diameter, Length, and Lead Spacing

Life & Temperature

Product

Packaging

Screw Terminal Electrolytic Capacitors

Snap-In Electrolytic Capacitors

Film Capacitor Basics

Searching for Film Capacitors

Ceramic Capacitor Basics

Searching for Ceramic Capacitors

Speaker Crossover Capcaitors

Conclusion

Share this:

Share this:

Share this:

Bose 901 Series I and II Background

Bose 901 Direct/Reflecting Speaker System – Series I and II

Bose 901 Series I Active Equalizer

Series 1 Early Production

Series 1 Mass Production

Bose 901 Series II Active Equalizer

Bose 800 Professional PA System

Bose 800 Active Equalizer

Mods & Bodges

Postscript

Share this:

Share this:

Bose Active Equalizers

1934 HMV 444

Sony TA-5650 VFET Stereo Receiver

Share this:

Share this:

Share this:

Share this:

Share this:

Find:

About Me

Blogs

Friends

Resources

Categories

Meta