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!

ba-cr8

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.

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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

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!

Posted in Uncategorized | 10 Comments

Creek 4140 S2 Overhaul and Voltage Conversion

Posted on August 23, 2015 by retrovoltage

This Creek 4140 S2 amplifier is a bit newer than most through the shop, although it’s getting up there. This particular one was constructed in 1989, and came via eBay from the UK configured for 220V power. The owner wanted it checked out and converted over to a U.S. power supply.

It’s an unassuming little amplifier, delivering 30W per channel at 0.1% THD. Inside, it’s pretty simply built but very clean. The shop has a universal power transformer that accepts nearly every plug style in both voltages, so it was easy to check out. The amplifier “worked”, although you had to crank the volume all the way up to maximum – the signal was getting attenuated along the way but it was still passing all the way through.

Because of the small number of capacitors in this unit, I recommended they all be replaced, and found that two of the small signal capacitors had gone very low in value towards being open. With the capacitors replaced, the unit came to life on 220V just fine.

The owner supplied a 120V transformer for this amplifier to swap. Theoretically, according to the schematic, the transformer has a split primary which can be wired in series or parallel for either voltage, but in practice there was no sign of the extra taps, so it was just a direct swap-over.

Transformer leads are enameled wire, which needs to be scraped down to the bare copper in order to take solder. Then the leads were joined back to the same colors.

Finally, it was time to swap the plug with a U.S. fitting.

Time for some testing! The Creek 4140 S2 is rated for 20 Hz – 20 kHz, with 0.1% THD at 1 kHz. How’d it do? The Audio Precision System One analyzer gave some insight. Frequency response from 20 Hz – 20 kHz was flat +/- 1 dB, which is fantastic.

On the extended range frequency response test, the actual -1 dB point was at 20 Hz on the low end and 30 kHz on the high end; +/- 3 dB at 10 Hz and 60 kHz. The channels are slightly imbalanced by 1 dB, even after bias adjustment, but not enough to worry about tracking down. This looks exaggerated due to the scale, but in reality, this is a perfectly good result and that difference would be on the bare verge of hearing only if you had perfect ears; otherwise it would be indistinguishable.

The amplifier delivered < 0.07% THD at 1 kHz, and overall had acceptable distortion performance.

Quite a few parts came out of this one!

A listening test proved this little amp sounded great, and so it was time to clean up and send it home.

The owner later sent in 2 more to overhaul the same way, he was pleased with this result.

Posted in Audio, Electronics, Projects | Tagged , , , | 1 Comment

New Test Equipment Day!

Posted on August 19, 2015 by retrovoltage

I’ve added a new analysis system to my stereo bench…the Audio Precision System One.

Amplifier measurements just got a whole lot more precise.

Posted in Commentary, Test Equipment, Tools, Toys | Leave a comment

1963 Fisher FM-100-B Stereo FM Tuner Overhaul

Posted on August 9, 2015 by retrovoltage

Something a bit unusual came through the shop recently, an old tube-type Fisher FM-100-B Stereo FM tuner.

Anyone who knows classic tube audio knows Fisher, and the FM-100-B sure lives up to the name. It’s a 12-tube FM/MPX Only tuner with a solid-state rectifier, designed to mate with a similar line of pre- and main amplifiers. These were occasionally found standalone, and also built into wide stereo consoles.

Some of the Fisher’s great FM performance came from the “Golden Cascode” 6DJ8 RF amplifier stage on the front end. You can’t have great-sounding stereo without a strong input signal, and the Fisher’s input stage delivers.

The rest of the tubes are 6AU6s, 12AX7s and 12AT7s primarily. Underneath, there’s a lot going on:

The owner wanted a recap and alignment, reporting that while it had been working the last time he used it, it wasn’t sounding great. There’s a handful of dipped capacitors, along with the power supply electrolytics, which needed a good going-over. Where possible, I replaced 0.5-1 uF electrolytic capacitors with film for longevity.

Next, on to the power supply. It’s a set of 4 x 40 uF capacitors in a can. I’ve selected a set of top of the line Nichicon capacitors with a 10,000 hour minimum lifetime and ripple tolerance about double what this set will experience. First step was to attach some terminal strips to mount the new caps:

By using terminal strips in this fashion, it’s easy to just move the components over to the new tie points and easily preserve the wiring layout with a minimum of disruption. A second strip on the other side finishes out the set of 4 caps:

The replacement is finished off by clipping the now-useless terminals from the can capacitor, so it will never be used again:

After the first power-up, though, there was no sound. Time to check the tubes:

Found a dead 6AU6! That would do it, no signal was making it past the final demodulation step. A replacement fixed it right up. Then, on to the alignment.

First step was to reset the output level to 0 dBm (0.77V).

Then it was time for the alignment, by adjusting the cores for minimum distortion:

I also adjusted the MPX sub-chassis, including 19 and 38 kHz coils and the stereo separation adjustment, achieving equal stereo separation nearly -30 dB per channel. Not too bad. Solid-state tuners can achieve a little better separation, but not much.

Replaced parts:

All fixed up and adjusted, this Fisher tuner sounds fantastic with a great deep and rich tone and great clarity all the way up through it’s frequency range. Paired with a strong antenna and matching stereo system, it’ll be a fantastic performer.

Posted in Audio, Electronics, Radios and Tubes, Stereo, Vintage | Tagged , , , , , | 3 Comments

Revitalize HP and Tek digital scopes with a NewScope LCD kit

Posted on August 1, 2015 by retrovoltage

I’ve been trying to figure out if I want to bother repairing my old HP 1222A oscilloscope which I’ve been using as a waveform monitor attached to the scope ports of my Sencore PA81 Stereo Power Amplifier Analyzer. It’s been run hard over its lifetime from the looks of it, and the CRT is so dim now that with brightness turned all the way up to maximum, you can just barely see the trace if you shield it from external light. It’s an older model, from the late ’70s, but it makes a good audio scope.

While a replacement CRT seems hard to come by, I did stumble across an interesting solution for some of the later digital display oscilloscopes and analyzers: the Simmconn Labs NewScope modules! I’m not affiliated with them at all, but it looks like an interesting product that could preserve a lot of the highly reliable digital gear which just happens to be old and have worn out display sections.

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They’re really interesting upgrade modules, which add color and clarity to the old display screens, and have some other interesting features like saving traces, etc. which may not have been available on earlier models. These come in several models, designed to work with:

  • 3577A, 3577B Network Analyzer
  • 3562A Dynamic Signal Analyzer
  • 3563A Dynamic Signal Analyzer
  • 8756A Scalar Network Analyzer
  • 4145A, 4145B Semiconductor Parameter Analyzer
  • 8566A, 8566B Spectrum Analyzer
  • 8568A, 8568B Spectrum Analyzer
  • 8567A Spectrum Analyzer
  • 8753A, 8753B Network Analyzer
  • 8757A Scalar Network Analyzer
  • 8702A Lightwave Component Analyzer
  • 8720A Network Analyzer

And some Tektronix scopes, too:

  • TDS 520A 540A 620A 640A
  • TDS 520B 540B 620B 680B
  • TDS 520C 540C 580C 680C
  • TDS 520D 540D 580D
  • TDS 644A 644B 654C
  • TDS 684A 684B 684C 694C
  • TDS 724A 724C 724D 714L
  • TDS 744A 754C 754D
  • TDS 784A 784C 784D 794D

Worth checking out if you’re in the market!

[NewScope LCD Modules]

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Sony ST-J75 Recap and Alignment

Posted on July 31, 2015 by retrovoltage

The Sony ST-J75 is a pretty well regarded, great sounding stereo FM tuner from the early ’80s. It’s one of the first forrays into digital tuning, with a frequency read-out, programmable memory, and seek/scan functionality and variable muting driven by a microprocessor.

This model features FM only, accepts a 75 or 300 Ohm antenna, and outputs left and right channels at fixed 0 dBm (0.77V) level. Inside, the board is quite well laid out and accessible:

The owner reported it didn’t sound great and generally needed to be reconditioned. Taking the cover off, you could see where the capacitors had been outgassing due to failures!

The bottom cover comes off, too, allowing service without removing the board from the enclosure:

Component replacement was uneventful:

First power-up, it started pulling in some stations, but was fairly far out of adjustment.

Time for alignment! The service manual has a very detailed alignment procedure for this receiver, including adjusting various voltage references, clocks, levels, and offsets. This process used a large assortment of test equipment including an HP 3585A spectrum analyzer, Sencore PA81 Stereo Power Amplifier Analyzer, Sencore SG80 AM/FM Stereo Analyzer, and Keithley 2015 THD multimeter.

First up was setting the levels:

Next, to align the discriminator:

Adjusting stereo separation was next.

Using the SG80 and the PA81, I checked the existing stereo separation and found it to be approximately -40 dB; this figure is within spec and did not require further adjustment.

FM Stereo contains signal information up to about 17 kHz, then drops off to allow for separation of the 19 kHz stereo sub-carrier which contains the stereo coding on the sub-carrier. Because this 19 kHz is within range of the audio frequency, MPX decoders have a 19 kHz rejection trap which removes the remaining 19 kHz carrier from the audio, but leaves the decoded stereo information. This adjustment should be set for a minimum. The service manual procedure for this adjustment was somewhat complex and in fact I was not able to complete it the way the manual recommended.

Fortunately, though, I have considerably better test gear than what Sony imagined a stereo shop might have at the time, and using the HP 3585A spectrum analyzer I was able to see and adjust the 19 kHz peak correctly.

The 19 kHz peak is shown at this marker, below the prevailing signal level:

With that, all sealed back up! It sounds great in both mono and stereo now.

Classic looks, and sounds great!

Posted in Audio, Electronics, Hi-Fi, Stereo | Tagged , , , , , | Leave a comment