Are Kids the Future of Ham Radio?

Posted on November 22, 2015 by retrovoltage

Bob K0NR has an alternate take on how to keep ham radio alive as many of its practitioners age up:

For whatever reason, it seems that most people find themselves in a situation as an adult that causes them to say “I want to get my ham radio license.” When asked why they want to get their ham license, the top response is always emergency/disaster communications, followed by backcountry communications, pursuing electronics as a hobby and learning about radio communications. I suspect that starting to be established in a community and having some disposable income also play a role.

My hypothesis is that the most effective way of growing a vibrant ham radio community is to target adults ages 25 to 40.

He’s got some data to back it up from the tech license classes he teaches:

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Hard to argue with those numbers. I passed my tech (and general) at about 25, but it was definitely for those reasons: emergency communications, backcountry communications (such as while skiing), and relating to my existing electronics hobby. In high school and college, I had way too much going on – not to mention not as developed of an interest in electronics in the first place – to pay any attention to ham radio.

Not that I’m doing much better now, my only operation so far has been a handful of sessions on 70cm Simplex with cheap HTs to communicate with another vehicle in something of a convoy situation.

Are you a ham radio operator? What do you think?

[The K0NR Radio Site]

Posted in Commentary, Ham Radio | Tagged , , , , , , | 1 Comment

Harman-Kardon Festival D-1000 Tube Receiver Repair

Posted on November 17, 2015 by retrovoltage

All vintage gear has a story to tell, but something really rare and interesting recently came across the bench: the Harman-Kardon Festival D-1000.

While it looks somewhat unassuming, a fairly straightforward 15-tube receiver with push-pull 6L6GC outputs and an AM and FM tuner, it’s definitely more than meets the eye: the Festival D-1000 was the very first commercially produced integrated stereo receiver!

Produced in 1954, the concept of combining a pre-amp, power amplifier, and tuner into one as our modern receivers due had been mulled about for a while but it proved a significant engineering challenge. Harman Kardon changed all that with their release of the Festival D-1000 receiver.

Harman-Kardon did have to make some design compromises to fit everything into this package, so while it’s a solid performer, if one were looking the absolute best sound at the time it would still be separates.

This one came from a storage unit, and it was due for an overhaul before being put into service. First up was testing all the tubes – and they all passed! The 5881 outputs were replaced the 6L6GCs, but they’re interchangeable.

Underneath it looks like it had never been serviced before:

Spot-checking the resistors, the sample I selected were all within their tolerance. Harman-Kardon must have used a good quality resistor with a protective coating – it’s quite unusual to find a unit this old where the resistors check out. So it was on to capacitors:

Adding some terminal strips for the power supply capacitors:

Component replacement complete!

Next up was an alignment. The FM reception distortion started off a bit above 0.5%, which is definitely pretty far out of adjustment; it finished out around 0.05%. Much better!

After following the factory alignment instructions, FM cleaned up very nicely, and AM was much improved!

All fixed up, this receiver will be a fantastic addition to any hi-fi collection, and will be a great performer for years to come.

Posted in Audio, Electronics, Hi-Fi, Vintage | Tagged , , , | 4 Comments

Harman-Kardon Citation 11 Pre-Amp Overhaul

Posted on November 11, 2015 by retrovoltage

A neighbor brought me his brother’s Citation 11 for a full overhaul. After a few decades of faithful stereo reproduction, then a number of years in storage, it was time for an overhaul to get it working good as new again!

Of course, everyone knows Harman-Kardon’s quality, and this Citation 11 is no exception. It’s a beautifully constructed piece of stereo history, and unusually features a 5-band graphic equalizer on the front to help you fine-tune the output to your listening environment and personal taste.

These are also a real pleasure to work on – all of the circuitry is fitted on plug-in cards which makes it a breeze to pull and inspect the different components. And underneath, the wiring harnesses are labeled clearly and effectively:

As with most stereo pre-amps, there’s quite a few components to replace, but it was easy pulling out the cards.

There was some evidence of past repairs:

But overall it was in great shape.

One interesting thing is that, while the boards are very well marked with component values, the installed components didn’t necessarily line up. Shown here, the board is labeled for a 100 uF 50V part but a 16V part was installed. Those ended up being replaced with 63V capacitors.

Underneath there were a couple of capacitors to replace:

And the big can up top! This involved converting from the old terminals to screw terminals.

This particular pre-amp doesn’t have any adjustments to make, so that was that! A thorough control cleaning later to clean up the crackles and pops while making adjustments and it was good as new.

Looks as good as it sounds!

Posted in Audio, Electronics, Projects, Stereo, Vintage | Tagged , , , , | 16 Comments

The Speaker Spotter – November 6th, 2015

Posted on November 6, 2015 by retrovoltage

Today’s Speaker Spotter showing the most interesting speakers for sale on the local Craigslist has a number of rare, unusual, and high-end speakers you’re not likely to find anywhere else. 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!

Microtower MT1 Stereo Speakers
$60 in Lakewood, WA

Interesting looking, if somewhat questionable in performance, these speaker towers feature a crossover-less pair of 4.5″ drivers mounted on either side, and a large port on the bottom. Maybe an early example of a waveguide-type speaker enclosure to accentuate the bass response which would otherwise be limited by the driver size? Might be a worthwhile addition to a collection if you’re up for the risk.

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Realistic Nova 10 Speakers
$100 in Kirkland, WA

Radio Shack’s Realistic brand equipment often gets knocked, but their vintage speaker offerings – especially the higher end ones like these Nova 10s – are quite good quality and are fairly collectible. These 50W 2-way speakers feature a tweeter, large woofer, and passive radiator and look to be in very good cosmetic condition.

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KEF KM1 Active Studio Monitors
$6000 in Puyallup, WA

These very unusual active studio monitors from KEF are a fully integrated, active design, featuring 4x100W, 2x350W, and 1x400W amplifiers for the bass, midrage, and treble respectively which should provide plenty of headroom for even the most demanding source material, and frequency response from 38 Hz-23 kHz. A little disappointing that with such bass power, the frequency response doesn’t extend down to 20 Hz, but relatively little music actually happens that low anyway so it’s not a  huge loss.

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Sansui SP-1500 3-Way Speakers
$140 in Olympia, WA

Swap out a couple of crossover capacitors and you’ll have a fantastic sounding, beautiful set of vintage Japanese lattice-grille speakers. I used to own a set of these myself, they’re great performers when paired with a suitable amplifier, and they really look fantastic in any room.

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Sony APM-55 Speakers
$500 in the Renton Highlands

Sony doesn’t get a lot of love today (although their yellow Kevlar-coned speakers are actually quite good sounding and have very extended treble frequency response great for EDM, at the expense of being very inefficient) but their vintage offerings were quite well respected. These big, powerful 3-way speakers offer the very unusual set of square-framed woofers and midranges, too. Definitely something different!

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Vintage Olson 12″ Triaxial Speakers in Barzilay Cabinets
$300 in Seattle, WA

From the late ’60s/early ’70s, these Olson triaxial speakers were a good attempt to reduce phase distortion and present as more of a point source. They’re very efficient, although don’t always have the flattest frequency response. With a 12″ woofer, midrange whizzer and horn tweeter stacked coaxially these should be a very interesting addition to any speaker collection.

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Epicure M201 Speakers
$175 in Seattle, WA

Epicure speakers are known for their construction and sound quality, and these M201 speakers are no exception. The M201s feature a pair of woofers and a pair of tweeters on each cabinet, one mounted forward-firing and one at an angle, to provide a wider and more immersive sound field. Butyl rubber surrounds means there’s no need to re-foam them, either! This listing also comes with a single EPI 100 speaker, “half” of an M201. Maybe a good center-channel?

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Empire Grenadier 800 Table Speakers
$250 in Olympia, WA

These interesting table-stand speakers feature a front-firing midrange and tweeter, a downward-firing 15″ woofer, and an interesting columnar design with marble tabletops on both. They look to be in great shape, and might be a good addition if you’re looking to add some sound to a room where more obvious speakers might not fit in. Reports on the Internet are that the woofer on these often comes out of alignment due to the effects of gravity on the woofer while being stored, but it can be re-seated easily enough by turning them upside down and playing a low bass note through them for 24-48 hours. Likely not an issue if they’ve been played recently, though!

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STR Omega II Speakers
$239 in Snohomish, WA

A fairly rare speaker from the ’70s, these stretched the upper boundaries of a home speaker and were getting into the range of PA/commercial speaker territory. Featuring a pair of downward-firing 12″ woofers, a 6″ midrange and dome tweeter in front, and a horn tweeter firing to the rear these certainly will offer a lot of sound. On the back are provisions for bi- or tri-amping, depending on your setup, or you can use the common input and internal crossovers. Big and heavy, but very interesting!

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Infinity Reference RS 2.5 Speakers
$1275 in Des Moines, WA

Infinity speakers, especially their older vintage models, are fantastic in quality and often feature electrostatic/ribbon midranges and tweeters, the RS 2.5s are no exception. These freshly-refrubished units feature a large 12″ woofer and electrostatic mid-ranges and tweeters in an array. These are one of the smaller Reference RS series, but certainly pack a punch. One benefit is the active equalizer required for correct operation is integrated directly into these speakers, unlike other bigger models where it’s a separate box that can get lost or damaged. I’d buy these if I had room for them in a heartbeat!

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Like some of these speakers? Click through to the ad and contact the seller!

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

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

Posted on November 2, 2015 by retrovoltage

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.

RCAChanalyst02

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.

Posted in Commentary, DIY, Electronics, Gadgets, Test Equipment | Tagged , , , , | 2 Comments

1937 Zenith 5-S-126 Tune-Up

Posted on October 30, 2015 by retrovoltage

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!

Posted in Audio, Bose, Projects | Tagged , , , , , | 6 Comments

Antenna Distribution for AM Radios

Posted on October 24, 2015 by retrovoltage

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.

ins-afhd-4

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.

ins-mbs-4

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

Posted on October 9, 2015 by retrovoltage

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

Posted on September 30, 2015 by retrovoltage

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.

bose-201-s2-2

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.

pioneer-cs33a

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!

tannoy-revolution-r1

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.

kef-103-3

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.

polk-rti-a1

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

Sherwood S3000-V Stereo FM Tuner Repair

Posted on September 28, 2015 by retrovoltage

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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