Bose® 901 Series I Active Equalizer #48344 Repaired

From the Rain City Audio Repair Blog:

Another classic Bose® Active Equalizer came through the shop recently for a standard overhaul from sunny California. It’s owner reported that it was performing poorly and channels would cut out. Sounds like a good time for a rebuild!

Inside, it looks like 6 of the 7 secondary filter capacitors and one channel’s output capacitors were replaced in the late ’70s or early ’80s.

This unit got all new parts, including silver solder, film output capacitors as an upgrade from the electrolytics, and a thorough cleaning.

The indicator lamp was flickering, so it too was replaced with a new neon bulb to illuminate the power switch.

Fully restored, this Active Equalizer is going to be a fantastic performer for many years to come!

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Mailbag: What’s the best multitester for vintage radios?

I recently got this question in the mailbag, and it seemed like a good one to answer:

What’s the best multitester for vintage radio repair?

That’s actually a tougher question than it seems. The short answer? Well…it depends a bit, but most multitesters (not to be confused with multimeters, which are very useful) aren’t that useful for vintage radio work. They’re not a bad thing to have, but most of their functionality is lost on a vintage radio.

To re-cap, a multitester is a neat little microcontroller instrument which can do quick analysis of 2- and 3-terminal devices. It’s useful for checking capacitor value and ESR, quickly checking transistors and FETs, checking diode voltage drop and capacitance, measuring DCR and inductance of coils, and low-ohms resistance measurements. Powered by a 9V battery and a microcontroller, these devices take a lot of the guesswork out of quick go/no-go checks for a variety of types of electrical components. The most common model is the MK-168, available from a ton of different vendors primarily on eBay for $20-50.

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The trouble with these devices for vintage radio repair is that you won’t end up using them all that often. Resistance measurements for vintage radio can easily be handled by most multimeters, like those in my Basic Tools round-up. Transistors started turning up at the very, very end of the tube radio era and you’re unlikely to encounter one of those hybrids and multi-testers can’t do anything for a tube beyond what a regular multimeter can. While DCR and inductance of coils is occasionally something to consider, more often than not you’ll have a good coil or an open coil and not a lot of in-between. And with vintage radios (and even most stereo gear through the ’80s) it’s just not worth it to test individual components before replacing; you’re better off just replacing all the parts subject to failure at once regardless of what they might measure. Not to mention, with a 9V battery supplying the power, you’re going to be far below the hundreds of volts found in most vintage devices.

That said, if you want the vintage equivalent of a multi-tester for a vintage radio, you do have a few options.

First would be a signal tracer. Signal tracers are fairly straightforward devices with a probe, detector, amplifier, and speaker. By injecting a tone at the antenna terminals of your radio under test and moving the probe through the signal path, you can find where it disappears. The probe can detect an AM RF or IF envelope and turn it into audio or amplify a small audio signal to find out which stage of the radio fails to pass a signal. These fell out of fashion after about the 1960s, but you can still find them on eBay. They were typically made by bench service companies like Conar, EICO, Heathkit, Knight, PACO, Superior Instruments, and others. They’re all pretty much the same – although being old gear, if you buy one you’ll want to make sure it’s in good working order (or you refurbish it) and the probes, if any, are provided. You should pay less than $100 for a fully working model. You’ll need a signal generator to go along with the tracer, of course.

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Secondly, if you have a bit bigger of a budget or like rare test equipment, you might consider an RCA-Rider Chanalyst.

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These are pretty rare and hard to find, but they’re unprecedented if you need a full functioned signal tracer and generator. These offer RF and IF generators, an oscillator injector, a power meter, and audio output (and you can even hook the various stages together and use one as it’s own radio if you wanted!) Sadly, though, these are rare and expensive and aren’t any better than a signal generator+signal tracer combo.

In general, though, I’m not sure I can really recommend a signal tracer if you’ll be doing more repair work than just vintage AM tube radios. They have little use in an FM radio, stereo receiver, or even most other electronics projects beyond a radio with the AM broadcast band and a 455-ish KHz IF. I used to have one, and used it once or twice very early on, but quickly moved up to other test gear and it sat taking up bench space until I finally got rid of it. About the only place they have any real use, in my opinion, would be tracking down issues with a radio’s front end – between, say, the antenna coil and a first RF amplifier ahead of the mixer – where signal levels might be too low for most oscilloscopes to display. Signal injection with a generator would likely be able to overcome this limitation, though.

So, in conclusion: in my opinion, a multi-tester isn’t a great tool if you’re just doing vintage radio repair. You’ll be better off with a plain old signal generator and tracer (along with your multimeter and standard bench tools) for your first set of vintage radio repair tools, if you’re not sure about taking the plunge for bigger and more expensive test equipment. Multitesters are fantastic little devices, but have limited applications in vintage radio repair, and so you’d be better off saving your money if that’s all you’re planning on working on. As far as signal tracers, while they are useful for vintage radio repair, they do have a limited usefulness beyond AM radios so keep that in mind when deciding if one is right for you or not.

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1937 Zenith 5-S-126 Tune-Up

From the Rain City Audio Repair Blog:

This very nice Zenith 5-S-126 came through the shop a little while ago. It was originally purchased by a local collector from eBay already restored and playing, and served well for a couple of years, until it started having some trouble.

The 5-S-126 is a 1937 Zenith radio, with 5 tubes and a 6″ speaker firing up through the top of the cabinet. It receives the AM broadcast band and two shortwave bands. The owner reported that it used to have great reception, but it had slowly picked up a bit of hum, as the reception faded to nothing.

The previous technician did a workable, if not especially pretty, repair job. I cleaned up some of the wiring, moving the two filter capacitors to more secure tie points and replacing them with brand new units for long life and reliability; the installed ones were starting to wear out. The radio then received an IF alignment which was pretty significantly off, but there was still no over-the-air reception.

That would be why! The 6A8 converter tube was dead, showing no emissions at all. Replacing it with a new old stock 6A8G tube brought the radio to life right away with great sensitivity and tone. Then it was back in the case and back home!

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Antenna Distribution for AM Radios

I’ve had a few questions come my way about antenna distribution systems for AM radios, specifically to connect something like a large attic antenna to multiple radios at once. There’s a lot out there designed for VHF/UHF or CATV signals, but relatively little designed to operate way down at the AM broadcast band frequencies from 0.5 MHz to about 1.7 MHz.

After some investigation, though, there does seem to be a set of products which would do the job. DX Engineering, a popular amateur and shortwave equipment vendor, has most of the gear for sale. First, most distribution systems are expecting a specific impedance, usually 50- or 75-Ohms, so you’ll want to start with the right antenna.

First up is the AFHD-4 antenna. It’s meant to be mounted in the attic or outside and fed with RG-6 coax into the house. It’s also a good FM antenna, so it could be useful for other types of receivers than just vintage radios.

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Next up, to run this out to multiple radios, you’ll need the signal splitter to provide multiple outputs. DX Engineering also offers their MBS-4 splitter, with one input to 4 outputs, covering 0.5-2400 MHz. Looks similar to a Cable TV splitter, but the frequency range goes much lower.

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Finally, since most vintage radios (or even ’70s stereo receivers) don’t have 75-Ohm coax ports on the back, you’ll need a matching transformer – one of the ubiquitous 75-300 Ohm baluns which was a lot more common back in the analog television days, but still kicks around from time to time. It will convert from the 75 Ohm coax signal to a 300 Ohm leaded connection, which you can connect across your radio’s antenna and ground terminals. Reportedly, the Channel Master CM 94444 is a good choice with low insertion loss, but you may have to experiment a bit as most of these aren’t specifically measured for performance at AM frequencies. They’re cheap if you need to try a few different ones to find some that work well, though.

In addition to being easier to hook up, these matching transformers are useful for adapting the impedance to be closer to what a vintage radio will expect for better signal transfer.

Depending on your radio, and the lengths of the coax run, you might not actually need the balun/matching transformer. It does terminate the 75-Ohm coax into it’s characteristic impedance, so it works like a real transmission line and has relatively low loss, but depending on your local environment the twin leads might act as their own antennas and cause cross-talk and interference. You’ll want to experiment to find out for sure.

cm94444

To put it all together in a working system, mount up the antenna in your attic or outside on your roof, then run coax to a convenient drop point and install the splitter. Now, depending on how strong your local stations are, you might not need any other equipment – but the MBS-4 splitter has 12 dB insertion loss, so you might want something to help boost the signal levels up. In that case, there’s another DX Engineering product, the InLogis LF/MF/HF receiving pre-amp. It offers 30 dB of gain on the front-end; install the amplifier between the antenna and splitter and you’ll have a great signal boosting system. If it’s too much, knock it back down a bit with 10 or 20 dB fixed attenuators to dial in just the right amount of gain you’ll need. (The amplifier system is a little spendy, at $300 with free shipping, and has a bit of a lead time on it. There are some included features which are geared more for ham radio users which drive the price up a bit.)

ins-rf-30b_xl

And of course, you might need some accessories. There’s the already-mentioned matching transformer; you might also want to pick up a spool of RG-6 coax for the new runs you’ll be making to distribute the signal to your radios. And if you don’t already have a coax crimping kit, that’s helpful. And finally, you may want some attenuator pads to fine-tune the signal level reaching your radios after the amplifier and splitter if you have trouble with the front ends overloading.

In total, if you pick up the antenna, amplifier, splitter, spool of coax cable and crimping kit, and four matching transformers you’re looking at about $600 for the full set of equipment. Sounds a little steep, but it’s a high end solution which should provide great performance and far less hassle than trying to build your own or cobble something together with parts which weren’t designed for this application.

Posted in DIY, Electronics, Gadgets, Radio, Resources | Tagged , , , , , , , , | 9 Comments

Hands On with the FLIR One for Android

Several months ago I ordered a FLIR One for Android, a small attachment which adds infrared thermal vision capabilities to most Android smartphones and tablets. After the backlog of pre-orders finally cleared out, I got my hands on mine today!

FLIR, of course, has been around in the military and industrial arenas for many years making things like heat sensors used by engineers, thermal rifle scopes, thermal sensors on heat-seeking missles so on. They’ve had a few previous consumer products, including a somewhat less capable version for the iPhone 5S only, but this is an improved and mass-marketed upgrade which looks like a ton of fun.

The FLIR isn’t the only game in town even as far as thermal Android smartphone attachments go, but it’s the only one to feature MSX technology which overlays a wireframe of the visible light image on top of the thermal image, giving it more context. It’s not just blurry heat blobs, which makes it way more useful.

Let’s unbox it!

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I was surprised by the clean and easy to access packaging.

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That’s it! The unit plugs into your phone’s micro-USB port for its data connection, but it’s actually powered exclusively through an internal battery, charged by the FLIR One’s own micro-USB port on the side which has a reported runtime of about 45 minutes. The battery status is available in the companion app, and it can charge from the external charging power while also in use.

The companion FLIR One app is installed from the Google Play Store. It’s a little quirky on my phone, but nothing too bad. It’s important in my experience to have the sensor plugged in and turned on prior to launching the app, or you need to close and re-launch, even though the app does seem to imply that it can be hot-plugged. Maybe on certain phone models it can, but not my Xperia Z3.

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This add-on is clearly designed for phones with the USB port on the bottom center as there is no software provision for rotating it’s orientation. On my phone, with the USB port on the side, this is a bit annoying but a short extension cable would fix that. The app is fairly no-frills, and could definitely use some polishing compared with the very sleek physical product that it drives.

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Sadly, the phone’s hard shutter button doesn’t cause the FLIR One app to take a photo, you have to use the on-screen button. In addition, most of the controls are un-labeled – and there’s no “Help” menu, or manual included in the package.

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Because the sensor combines a visible-light image with the infrared image, there’s an option to turn the light on (top row left) which crashes the app. There’s also 3 and 10-second self timers, a setting I’m not sure of on the top row far right, a macro setting of some kind on the bottom row, and the settings slider. Selecting the Macro button brings up a slider to adjust the camera parallax, but I don’t see anything actually change while moving it.

You can also turn on the temperature display. It’s fixed to display the temperature of the center point of the image.

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There’s a few other modes, including thermal video, panorama, and time-lapse.

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And a number of different color pallets and color weights to help visualize what you’re seeing. One complaint from Internet users is that, while you can pick from a number of emissivity pre-sets (Matte, Semi-Matte, Semi-Gloss or Gloss) there’s no option to enter a defined emissivity, if you happen to know it for the material you’re measuring.

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Lack of emissivity settings isn’t a problem for me, though, as I’m primarily going to use this to measure heat dissipation in stereo receivers and radios to ensure correct operation.

My impression is that the software feels pretty clunky, which in my experience is common when hardware companies have to write actual software. Most of the companion PC apps for lab test equipment that I have are awful to use, too, so I’m going to chalk this up to early-adopter pains, but I expect as more of these get out to consumer’s hands the app will evolve to be more user-friendly.

Even with clunky software, though, this is a really fun toy to play with and it’s going to be a very useful tool once I take it up to the shop. In addition to my use, checking electronics for faults, it would be great for checking for insulation and leaks in your home or car, seeing what that noise was in the backyard, or any number of other things that rely on heat more than light.

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I also took some photos of my workbench.

I need to add my isolation transformer to a switch! I’ve never noticed that it’s idle current generates some noticeable heat. It’s only slightly warm on the touch but it lights up on infrared.

Laptop and cell phones:

What gets hot in a Bose equalizer?

Interestingly, one of the rectifier diodes is dissipating heat but the other is totally cool.

All in all, a good buy! Available from Amazon for $249.

Posted in Electronics, Gadgets, Technology, Test Equipment | Tagged , , , , , , , | 1 Comment

The Speaker Spotter – September 30th, 2015

It’s back! Another installment in this occasional series, “The Speaker Spotter”, picking out the most interesting speakers available on my local Craigslist. Today’s Speaker Spotter focuses on bookshelf speakers for the best sound possible in a small package. As always, I’m not affiliated with any of these sellers, and if the ad is gone then it’s likely the speaker sold already.

Here’s what’s interesting this week!

Bose® Direct/Reflecting Speakers – Model 201 Series II
$40 in Lakewood, WA

Bose doesn’t get a lot of love in audiophile circles, but I’m a pretty big fan myself, and these 201 Series II speakers are back from the era where they devoted a bit more to quality engineering than many of their products do today. I’ve heard various sets of 201s myself, and they provide a great room-filling sound with pleasant tone characteristics, as long as you don’t expect too much volume or earth-shattering bass.

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Boston Acoustics CR-8 Speakers
$100 in Port Townsend, WA

Boston Acoustics is a venerable audiophile speaker brand, and these little 2-way bookshelf speakers designed for 15-125W of power can deliver a pretty great 90 dB efficiency and should give a great, detailed sound. Some people find them to be a little bright, though – I prefer a bright sound signature personally, so that sounds right up my alley!

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Pioneer CS-33a Vintage Speakers
$149 in South Everett, WA

Pioneer vintage speakers are nicely well regarded, and these feature those beautiful latticework grilles they’re known for. Great looking shape for a speaker that was built in 1971! They’re very efficient but only accept up to 35W of output power, so proper amp pairing is a must with these.

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Tannoy Revolution R1 Bookshelf Speakers
$150 in Shoreline, WA

Tannoy is a well-known British hi-fi brand, and their speakers are top notch, from their flagship Westminster GR on down. These little speakers support bi-amplification and deliver 87 dB sensitivity at 8 Ohms, and I expect will sound fantastically accurate for any music source. Nice under-stated design and cherry finish, too!

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KEF 101/3 Reference Speakers
$199 in Lynnwood, WA

KEF is another UK speaker brand, with a very interesting time-aligned coaxial driver system to help these speakers present as more of a point-source, which can reduce certain kinds of phasing distortion you’d get from separately positioned drivers. This gives them a cool, monolithic design – although they, too, support bi-amplification just like most higher end speakers. They’re 6 ohms nominal, but that’s not a problem for many amplifiers these days, and they’re middle of the road efficient at 87 dB 1W*1m.

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Heco Phon 3 SF Speakers
$200 on Snoqualmie Ridge

These vintage German hi-fi speakers are a bit of a mystery. They look to have an interesting 3-way design, and the labeling indicates they’re 4 Ohm impedance speakers for 60-100W of power handling. Beyond that, they’re a bit of a mystery! Looks like this could be an interesting addition to any speaker collection.

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Polk Audio RTi A1 Bookshelf Speakers
$205 in Seattle’s Crown Hill neighborhood

Polk Audio’s offerings go down pretty far into the economy side of the spectrum, but their higher end offerings are quite good, and these RTi speakers are a respectable offering. They’re 89 dB efficient and offer extended treble frequency response to 27 kHz. Looks fantastic in the beautiful cherry finish, too! These routinely sell for around $300, so this is a pretty solid deal.

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ERA Design SAT 5 Bookshelf Speakers
$350 in Kirkland, WA

These are interesting little high-end bookshelf speakers. Nominally 6 Ohms ant 87 dB efficient with a long-throw 4″ woofer and horn-loaded 1″ dome tweeter, I expect they sound extremely crisp and efficient, and with that woofer design punch above their weight in the bass department – and High Fidelity Review agrees! Looks great in piano-black, too.

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JBL L-96 Bookshelf Monitors
$500 in Kirkland, WA

Anyone familiar with vintage speakers knows JBL and knows how great they sound. Recently re-foamed, these should be in good shape for decades to come. They’re pretty efficient at 89 dB, and the titanium dome tweeter provides incredible clarity and detail in the upper ranges. So much so, in fact, that people often turn the treble down a bit. A great addition to your collection if you’ve got the room and the cash!

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Like what you see? Click through to the ad and contact the seller!

Posted in Audio, Collections, Commentary, Hi-Fi, Speakers | Tagged , , , , | 1 Comment

Check Out LED Filament Light Bulbs: Classic Styling Meets High Efficiency

I’ve been using CFL bulbs in most of my light fixtures for a number of years. They’re a pretty solid, mature technology by now and have a ton of benefits over classic incandescent and even “eco-friendly” halogen bulbs. Where a 60W incandescent bulb might put out 800 lumens, and a halogen might use around 45W for the same amount of light output, CFLs offer the same light output from only around 15W of power. Lower waste heat has been a big goal in my lighting choices, since I live in an apartment which has very high heat retention, and lower-heat bulbs made a real difference.

One of my CFLs started making a buzzing noise after a few months, though, and when I pulled it for inspection I found a major hazard. The top had come separated from the base, leaving the guts fully exposed which had started to vibrate!

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That was a pretty dangerous failure. I pulled that one from service and replaced it (look for an article a bit later where I trace out the circuitry). I’ve been reading a bit about the new “LED filament” bulbs which combine the even greater efficiency of LED lighting with the classic filament look of the old-school incandescent bulbs, and so I ordered a few to try out.

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They’re pretty cool looking. It’s not quite the same as an incandescent (you can barely see the wires in those style of bulbs, these have visible tubes) but it’s pretty close. These are made possible by a new “silicon on glass” manufacturing method. The silicon LEDs are “printed” onto a glass substrate, which is then dipped in an epoxy resin coating to diffuse the light and provide the correct color balance. It’s a great way to get LED efficiency, when you need a light bulb that’s a bit more aesthetically pleasing than the chip-tower design:

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LED filament bulbs are incredibly efficient, too, only a tiny bit less so than a “standard” chip LED unit.

They’re made by a wide number of manufacturers by now, in the USA, Japan and China. I ordered a set of Chinese bulbs from eBay for myself, but they’re on Amazon as well. The Chinese ones are a bit cheaper, although Internet sources report the Chinese bulbs use a type of epoxy which becomes brittle after several hundred hours of operation – so if you find yourself moving your light bulbs between fixtures, or you’re using them in a mobile application, you might invest in a US or Japanese variant. The bulb I showed above, consumes only 8W of electricity and puts out 850-900 lumens, making it even more powerful while still being more efficient. eBay seller “torylee2013” has a good reputation and sells many styles of LED filament bulbs direct from the factory. They arrived in about a week and a half, with free shipping, too.

CrystalLED has a great “how it’s made” video, well worth a five-minute watch:

All in all, I’ve been very satisfied. They’re only slightly warm to the touch even after hours of operation, and look great. The one downside, though, is they do strobe a bit. It’s not even slightly noticeable in general, but it does give the blades of spinning fans a bit of a slow-motion effect if I’m looking for it. Nothing that I consider a problem!

I’ll be moving forward to replace all of my CFL bulbs with LED filament bulbs over the next few months I’m so satisfied.

LED Filament bulbs on Amazon

LED Filament bulbs on eBay

torylee2013’s eBay store

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Sherwood S3000-V Stereo FM Tuner Repair

From the Rain City Audio Repair Blog:

This Sherwood FM Stereo tuner came into the shop recently. It’s owner successfully completed a re-cap of the unit, but the specialized tools for performing an accurate FM Stereo alignment are beyond the reach of most hobbyists, and so he sent it into my shop for final adjustments to make it perfect. The owner reported it worked well on mono, but the stereo light never illuminated, and the dial tracking was a bit off.

The owner had done a good job on the re-cap, with nice clean joints, replacing all but the two output electrolytic caps.

Initial measurements validated the alignment; in mono it was receiving at about 1.6% THD.

Up first was a mono FM alignment, adjusting the cascode RF amplifier, oscillator, and IF chain to bring all the tuned circuits into proper adjustment, improve dial tracking, and center the tuning meter.

After those, and several more adjustments on the bottom side for the lower cores, distortion dropped off to around 0.05% under ideal conditions.

Unfortunately, there was no action on the stereo circuit even when fed from the Sencore SG80 generator. I spent some time tracing out the circuit to understand what’s going on:

One common problem on this style of tuner is that if the stereo indicator lamp has failed, the entire rest of the stereo circuit won’t operate. In this case, the lamp is a NE-2H neon bulb, which can lose its neon with age and fail to strike.

Swapping in a new bulb was the first step.

Success – now the receiver responds to the 19 kHz pilot signal!

Time to finalize the alignment, including the 19 Kc, 38 Kc coils and transformers, the 19 Kc null, and separation adjustment.

The 19 Kc null serves to remove residual 19 KHz audio from the final output signals. It’s adjusted for lowest 19 Kc level which provides proper stereo response.

All set! The indicator light correctly responds to stations transmitting in stereo, and there’s about 10 dB of separation between channels. Much more often just isn’t possible on a tube MPX design. All in all, it sounds great!

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Vintage Documentary: How Stereo Turntables Work

Documentary Tube on YouTube has digitized an excellent early video documentary discussing the newest hi-fi invention of the time: stereo! In this 4-minute video, the narrator compares mono with stereo recordings on vinyl. Worth checking out!

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Adding Capture to a Vintage Scanning Electron Microscope

Applied Science over at YouTube has a great video about adding a capture capabilities to a vintage scanning electron microscope, including some great videos of that instrument in action. Check it out:

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