This Bose 901 Series I Active Equalizer, serial #41550, came into my shop in need of an overhaul after being stored somewhere sticky for many years. After a rebuild and thorough control cleaning with high powered solvents, this equalizer performs good as new! All new capacitors, resistors, transistors and neon bulb will last for a long time to come.
Check it out at Rain City Audio
This 1936 Zenith 5-S-29 was in the shop for a complete overhaul with all new resistors and capacitors, a new dial lamp socket, tube testing and alignment. After all that service, it looks and sounds fantastic and is going to last for a long time to come in a local collection.
Check it out at Rain City Audio
This rare early shirt-pocket transistor radio, the Coronet TRN-6, needed a few new capacitors to sound its best. It delivers surprising performance from such a small package! Plenty of tear-down photos in this article.
Check it out at Rain City Audio
This Bose 901 Series II Active Equalizer got a full overhaul in the shop with all new capacitors, resistors, transistors and silicon diodes. After a thorough control cleaning, it sounds absolutely fantastic once again and should last for a long time to come.
Check it out at Rain City Audio
This 1958 Zenith Royal 500, an early 8-transistor portable AM radio, came into my shop for a complete overhaul. I replaced several badly out of spec capacitors, added some insulation to correct a short circuit in two of the batteries and gave it an alignment. This is a perfect radio to take to the beach or the park while listening to a ball game, just like they’d have done back then. Many tear-down photos inside!
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Rain City Audio is proud to announce a new product offering: capacitor repair kits for the Westinghouse H-126 Little Jewel / “Refrigerator” Antique Radio!
This repair kit contains the most commonly needed parts to refurbish your Westinghouse H-126 Little Jewel / Refrigerator radio. You’ll receive 13 modern, high quality replacement film and electrolytic capacitors to bring your radio up to full performance. Take the guesswork out of fixing your own collectible model of Little Jewel, and save the hassle of using a parts site like Digi-Key, and order a kitted set of parts that’s ready to replace.
Included in this kit:
1 x 0.001 uF (You’ll receive 0.001 uF)
1 x 0.2 uF (You’ll receive 0.22 uF)
2 x 0.04 uF (You’ll receive 0.047 uF)
1 x 0.005 uF (You’ll receive 0.0047 uF)
1 x 0.025 uF (You’ll receive 0.022 uF)
2 x 0.01 uF (You’ll receive 0.01 uF)
1 x 0.1 uF (You’ll receive 0.1 uF)
1 x 0.1 uF (You’ll receive an X1Y2 Safety Capacitor to replace the across-the-line RFI suppression capacitor.)
1 x 20 uF 50V Electrolytic (You’ll receive 22 uF 50V)
2 x 50 uF 450V Electrolytic (You’ll receive 47 uF 450V)
Westinghouse H-126 Little Jewel/Fridge Capacitor Kit – $39.00 with Free Shipping!
This Bose® 901 Series II Active Equalizer is a part of Rain City Audio’s parts stock and got a full rebuild with upgraded parts and complete and comprehensive testing. All transistors, resistors, film and electrolytic capacitors were replaced, a new neon bulb added, and the controls cleaned and lubricated. This very detailed repair walkthrough has photos showing the drifted carbon composition resistors which can throw off the equalizer’s curve even if all the capacitors have been replaced. Click through for many more photos!
Check it out at Rain City Audio
This iconic late ’60s GE clock radio came to the shop with loud, low humming when turned on and no radio reception. That’s a familiar problem! Time for new capacitors. This particular used a 100 uF main filter and several 200-400 uF secondary filter capacitors around the boards, along with three electrolytic coupling capacitors in the signal chain. They were very tired and as shown by the hum had started to short out; if the radio continued to be run with the loud hum it could have been badly damaged so it came in just in time. Some new components later, she’s good as new and sounds surprisingly good for such a small radio. There’s a mystery switch inside, too – do you know what it might control? Read more for more photos of the repair.
Check it out at Rain City Audio
This 1937 Westinghouse radio was the second highest in their tabletop line-up for ’37 and featured 7 tubes and a large, eye-catching dial for easy tuning. After a full overhaul including capacitors, resistors, an eye tube socket rebuild, new power cord, dial cord re-string, line input addition, and a full alignment it sounds great and pulls in stations across the dial. This model had the alignment trimmers all on the underside which was annoying, but peaked up nicely nonetheless. Read more for photos of the rebuild!
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This FADA 270T radio which came through the shop lately was a beautiful, very high end radio back in 1936. It has a huge airplane dial with dual-speed tuning and a magic eye indicator, and a beautifully organized under-chassis layout. Repair was pretty straightforward with a few surprises at the very end, but nothing that couldn’t be fixed. Click through to read more – there’s dozens of detailed, colorful photos of antique resistors and the magic tuning eye.
Check it out at Rain City Audio
This equalizer got a full overhaul with new 1% precision resistors, electrolytic capacitors, audiophile-grade output capacitors, transistors, gold-plated RCA jacks, 4% silver solder for all connections, a thorough switch cleaning, and computerized frequency response testing and a listening burn-in to verify proper operation. It sounds just fantastic with a very dynamic and life-like presence that really draws you into the experience of the source material, just like the Bose 901 should.
Check it out at Rain City Audio
Cross-posted from Rain City Audio:
I had a Phase Linear 2000 through my shop lately. It was running okay, but had some pops and clicks and the controls weren’t all that smooth. Time for an overhaul before anything worse cropped up!
This is a pretty fancy pre-amp made to be used with the Phase Linear 4000 power amplifier. It has a variable level output to be paired with a fixed input amplifier.
After fixing it up, I found this one to have a neutral, tight, almost laid-back sound without any extra embellishment. It was very nice – and part of that is owing to the very simple design.
The underside of the single-sided board Quality construction for the era. The bank of switches is an open design which gets gummed up easily but control cleaner easily solved that problem.
Of course, a pre-amp like this deserves nothing but the best: Nichicon Fine Gold series electrolytic capacitors.
The matching power amplifier will come up for service soon, so stay tuned! This Phase Linear is good as new and another piece of gear from the height of hi-fi is saved.
From the late ’50s, I had this nice example of an EICO HF-81 amplifier come through my shop. These are nice little stereo amplifiers with a built-in phono pre-amp and RIAA equalization and feature about 14W of power output per channel from a pair of push-pull EL84s each at about 1% distortion.
EICO was a popular brand of electronics kit maker back in the day. They made a lot of hobbyist or entry level shop test equipment (oscilloscopes, generators and testers) but had a handful of hi-fi stereo kits as hi-fi listening grew more and more popular. The fact they were assembled as kits makes them pretty straightforward to service, too – the layout is clean and there’s a lot of room on the chassis. It had been worked on a few times in the past – several coupling capacitors were replaced with early film caps in what looks to be the late ’60s/early ’70s. Just recently, the owner reported it was giving noise from one channel and took it to another local shop where the technician replaced a 50 uF capacitor (orange, bottom left) with a 100 uF cap that looks to me like it was probably an old-stock capacitor (blue, bottom left.) They’d clipped the old cap out of circuit but left its shell intact; not exactly what I’d call a best practice. More problems started cropping up shortly thereafter as the rest of the original capacitors degraded, so it came to me for an overhaul. After replacing the parts, there was still noise, distortion, and lower volume on one channel seen on the oscilloscope screen in yellow. Tracing through the circuit, it turns out the CRL couplets in the tone network were failing.
I fabricated new PCBs with the same values to replace the damaged parts and mounted them to the shield.
That fixed the problem right up! After some final tweaks and a burn-in test, she’s ready to go home. Lots of parts out of this one:
It’s going to sound great for years to come!
Rain City Audio Tube Audio Repair
Cross-posted from the Rain City Audio Repair Blog:
Bose® 901 Series IV equalizers are coming through the shop more regularly in the past year. It’s expected as these are definitely getting up there in years. This one was sounding muddy and not like it used to, so it came in for a full overhaul.
Manufacturing technology has reached the point by the Series IV that most of the film capacitors are reliable and don’t need to be replaced, but there are plenty of electrolytic capacitors, plus the original op-amps get noisy over the years and should be replaced as a matter of course.
This one received all new Nichicon Fine Gold electrolytic capacitors, and new TI TL072P op-amps.
If your Bose® Series IV Active Equalizer isn’t performing like it used to, Rain City Audio can help. Bose® Equalizer Repair Service
Cross-posted from the Rain City Audio Repair Blog:
Another Bose® 901 Series I Active Equalizer was through the shop lately, serial #33133. It came in working well enough on its original components for an overhaul and upgrade to ensure it lasts for a long time. It’s pretty unusual for these to still be running on original components so this was a bit of a surprise.
This one got all new parts. The electrolytic capacitors are all Nichicon Fine Gold audiophile electrolytic caps, with an even bigger upgrade on the output capacitors to high-end film capacitors with an ultra-low dissipation factor. It also got a new set of gold-plated RCA jacks to accommodate today’s thicker and more heavily shielded audio cables.
This equalizer is going to be a great focal point of a vintage stereo system for many years to come.
Rain City Audio Bose® Equalizer Repair Service
Cross-posted from the Rain City Audio Repair Blog:
Another Bose® 901 Series IV Active Equalizer came through the shop recently. It’s owner shipped it in without the wooden cover for security. This is a bad idea on the Series I/II, but for the III and later which have a rigid metal shell it’s a fine way to ensure the wood case isn’t damaged.
This one was sounding muddy and distorted, and it was time for an overhaul to keep it sounding like new. It has plenty of original electrolytic capacitors, along with old style vintage op-amp chips. The bridge rectifier is also made up of discrete diodes in this model; later used an integrated bridge package.
Interestingly, this is an earlier board revision with U101 in a different orientation than on later boards. It also shows evidence of having been replaced before – the stock filter capacitors were both 470 uF units; at some point in the past they’d been replaced with a 330 uF and a 1000 uF.
The op-amps had been replaced once before as well. This was a common factory repair on the earliest Series IV models, the chips occasionally suffered reliability problems. I doubt these were repaired by the factory, though, as Bose® factory service back in the day would never have used the wrong parts and damaged the PCB this much while soldering.
Pads were badly damaged, but I was able to repair them to make a good physical and electrical connection with the new chips.
With new electrolytic capacitors, new op-amp chips, and repaired traces on the bottom of the board this equalizer is back up to full performance and it should stay that way for a long time to come.
Rain City Audio Bose® Equalizer Repair Service
Cross-posted from the Rain City Audio Repair Blog:
I recently got to work on a very interesting piece of vintage stereo gear from the golden age of hi-fi in the ’70s, the Sony TA-5650 VFET Integrated Stereo Amplifier.
It’s a little rough, and while the power amp section works great the pre-amp doesn’t produce any output, this is a rare and interesting amplifier. In the output stage, the finals are Sony VFETs – a new and experimental type of vertically oriented FET which was being pioneered around this time. Sony used them in a small handful of receivers from the same year and never again in any other models or years; Yamaha produced a couple of models which used them as well, and oddly enough they turned up in a handful of 1990s MTX car audio power amplifiers – but overwhelmingly, it’s a rare and esoteric output device.
It’s also missing a knob.
It’s a well laid out amplifier inside: Towards the front, the final module with large bottom-mounted heat sinks and chimneys to the top-side vents for good airflow. The pre-amp controls, power supply, and rectifier are along the front and there’s a large power transformer.
A shot of the regulated power supply. As a part of the process, all the electrolytic capacitors get replaced. At this point in the process, the underlying cause of the pre-amp failure isn’t known, but that doesn’t change the procedure. The most likely cause of failures is often a failed electrolytic capacitor which leaks and damages near-by components. With the front face and knobs removed, the boards can be removed.
Overwhelmingly the capacitors were all replaced with Nichicon Fine Gold capacitors, although a handful in power supply circuits in high-ripple locations were replaced with other models with a better current capacity to ensure reliable operation. Unfortunately, however, this didn’t fix the problem: it turns out the 2SK76 small-signal VFETs were defective. That does mean this integrated amplifier will never have a functional pre-amp again, but it’s still a fantastic power amp stage.
The chimneys clip into the board supports, with the VFETs along the bottom. Removing it exposes the board to view.
One major reliability problem with these Sony VFET amplifiers, which has sent many of them to an early grave, is the varactor diodes used in the bias circuitry. They’re used to provide a stable, temperature-invariant voltage reference but unfortunately over age (aided by leaky capacitors) they tend to start to avalanche and fail to prove bias, instantly destroying the VFET output devices. They’re unobtanium, so if this happens, really the only source of new parts is another one that’s died for some other reason.
It’s not pretty, but it works: these VD-1221 varactor diodes can be replaced with a pair of 1N4148 in series.
One other issue with the Sony VFET series of amplifiers is the rectifier board. Sony used screw-in capacitors with a 10mm lead spacing; these are no longer manufactured. It was necessary to extend the leads and mount the board slightly on an offset. Again – not pretty, but completely functional.
After mounting everything back together, adjusting the power supply’s voltage reference, and adjusting the bias on both channels it was time for a burn-in test. This one plays very well with exceptionally low distortion, crisp and clear highs and a very triode-like midrange owing to the VFETs.
Quite a few parts were replaced during this repair – and I found a “new” chickenhead knob as requested by the owner to replace the missing knob (on the far right.) Fully reconditioned like this, it’s going to sound fantastic for a long time! These are pretty uncommon to find these days, so even with a bad pre-amp section it’s definitely worth the effort to repair – and with the low distortion and unique VFET sound it’s great for an audio enthusiast. This particular one belongs to a Grammy® Award-winning record producer if that gives you any idea of the quality and performance.
If you have a Sony VFET amplifier that needs a preventive overhaul to ensure it doesn’t meet an early demise, Rain City Audio can help!
Cross-posted from the Rain City Audio Repair Blog:
Another Bose® 901 Series I Active Equalizer came through the ship, Serial #46453. It came in with a variety of issues, just not sounding like it used to, and the owner requested a set of new audiophile-grade film output capacitors as an upgrade as well.
Based on the different ages of capacitors, it looks like this one was serviced some time in the late ’70s or possibly early ’80s. Several of the black capacitors had failed and were causing quality issues.
This particular one received Vishay and Panasonic signal capacitors in the intermediate stages.
After repair, this equalizer sounds perfect and the upgraded capacitors really bring out a lot of clarity and detail in the mid-range and upper frequencies. Paired with the 901 speakers, it makes a fantastic, room-filling, life-like sound and will last for a long time.
Rain City Audio Bose® Equalizer Repair Service
Cross-posted from the Rain City Audio Repair Blog:
I recently got to work on a Harman-Kardon Citation 17S pre-amplifier. Vintage HK gear is some of my favorite to work on: it’s robust, reliable, and built to be easy to service. The Citation 17 pre-amplifier is the companion for the Citation 12 power amplifier, and has a ton of features.
This one features a total of 6 inputs with 2 phono options, two tape loop outputs, and two pre-amp outputs which could drive a pair of power amplifiers.
Inside, it’s extremely open, and all of the circuit boards are mounted on edge connectors that can be easily removed for service outside the chassis.
There are 4 circuit cards with a variety of capacitors on them. These caps were starting to show their age, but weren’t quite dead yet, but several had high leakage and high ESR and were definitely not doing their jobs. This one was the worst, where internal leakage and heat was causing the skin of the capacitor to shrink and pull back.
Lots of replaced parts from this one! Testing showed it was performing perfectly after the service. I also cleaned the balance pot as it was a bit scratchy.
This pre-amp will continue to serve faithfully with its companion power amplifier for a long time to come, and deliver the detailed, accurate sound HK is known for.
Rain City Audio Vintage Stereo Repair
Cross-posted from the Rain City Audio Repair Blog:
Another Bose® 901 Series I Active Equalizer came through the shop recently for a full rebuild. These are all nearly 50 years old and are definitely showing their age, and this one was no exception – it came in with no output on one channel and definitely needed a full rebuild to get it going again. The Active Equalizer is responsible for shaping the audio signal to match the Direct/Reflecting driver’s frequency response, and without it, you’ll never get the good sound the 901 series is known for.
This one was pretty dirty, but nothing some rubbing alcohol and elbow grease couldn’t majorly improve. Inside, most of the electrolytic capacitors had been replaced at one point in the late 1970s, but were still 30-40 years old and well beyond their design lifetime. The rest of the components were all original, including the unreliable small signal capacitors in the center.
These original 2N5088s have color bands for their gain group on the back – all but one were identical. It looks like someone at the Bose® factory grabbed a wrong one during the original construction! Such a minor difference wouldn’t be noticeable to your ears, but might be able to be seen with sensitive test equipment, so it’s not a big deal. The transistors on this one came out and were replaced, since after the initial component replacement it still wasn’t quite right. One channel sounded great, but one channel had lower volume and suffered recessed mids which gave it an odd sound. Time for some troubleshooting!
Using my oscilloscope, I compared channels to see where the signal got lost, using the built-in math functionality to show the difference between the two channels. Ideally this difference should equal zero, a flat line, with both channels being identical.
After further probing and testing at different frequencies, the difference and phase shift were frequency dependent. That pointed me towards the crossover and feedback circuitry, where it turned out that channel’s 22 mH inductor had gone open and was no longer giving the right curve shapes. Replacing both inductors fixed it right up!
Problem solved! With that fixed up, I installed a new neon power lamp and boxed it up to go home, good as new.
Fully refurbished, this one is going to serve well for a long time to come!
If your Bose® Active Equalizer isn’t sounding like it should anymore, Rain City Audio can help.
