A change of pace from the Bose equalizers and hi-fi I’ve been working on a lot of lately, I had the pleasure of working on a 1936 GE Model A-52 antique radio.
This is a nicely designed and straightforward table radio with 5 tubes, AM and one Shortwave band. Back in the ’30s, RCA and GE shared chassis and designs quite closely and it’s no surprise this one uses all RCA metal tubes, 6A8 6K7 6Q7 6F6 5Z4.
This radio had been serviced in the past but was due for another go-around. Most of the capacitors had been replaced in the ’70s or ’80s, although there were a few that still needed to be replaced. I swapped the 4 capacitors which were definitely in need of replacement, but the other units tested fine and are recent enough I’m not too worried about them.
The radio power switch, though, had been bypassed. The radio’s owner reported the switch was sparking in the back. I tracked one down after several weeks and was able to get it installed and it functioned perfectly after that.
The radio’s alignment was already spot-on so no adjustments needed there. I re-assembled the radio and let it play for several hours of burn-in testing before sending it back to it’s home where it will continue to play beautifully for years to come.
Once in a rare while I’ll run across an old Bose Active Equalizer that I buy for myself, but they never last too long – I get a lot of requests to purchase a complete Bose 901 Series I equalizer to go with a set of speakers which long since lost the matching controller. I did just recently have one in stock and it went quickly; once they’re purchased I repair them on demand before sending them along.
This one’s all original as far as I can see. It was reported to have a dead channel when I purchased it, and the resistors had certainly drifted out of their tolerances with age. The case was in decent shape for being 40+ years old, too, although the light doesn’t quite catch it all very well.
Component replacement was pretty straightforward.
Some Bose 901 Series I and Series II equalizers used BC239C-labeled transistors, others used 2N5088s. They’re nearly identical – indeed, the rest of the circuit is identical – but they have a slightly different gain spec. Practically, this just translates into a slight difference in the volume control on your receiver – the generated curve is the same and both are identically factory specification compliant. When I need to replace transistors, I use all 2N5088s – but in this case, all transistors were good, so no replacement necessary! The neon bulb was flickering, though, so I replaced it with a brand new NE-2A and current limiting resistor. Then, a good solid control cleaning so all the switches moved freely and made good contact.
This one went to its permanent home next week where it should perform for many years to come! With precision metal foil resistors and new electrolytic and film capacitors, not to mention the very light duty cycle experienced by the equalizer (which draws only 1.5W total power consumption), mean it will be a long time until this needs service again.
I can repair your Bose 901 Series I, Series II, Series III or Series IV Active Equalizer for a low flat-rate with some optional upgrades. Most every one of the Series I equalizers needs to be reconditioned at this point. The majority of Series II do as well, and even the later series are coming up with defective capacitors and op-amps more regularly.
I’m happy to announce that starting soon, I’ll be offering professionally restuffed vintage capacitors for historically accurate repair and restoration of your antique radio! In my rebuild process, the old capacitor is carefully stripped of the old wax coating and the innards carefully removed. The body of the capacitor is lightly cleaned and a new high voltage axial lead film capacitor is installed in the cylinder. The ends are then filled with a medium density clay filler to provide stability, followed by a fresh coat of bee’s wax. The end product is nearly indistinguishable from one in original condition, perfect for performing a historically accurate repair of a valuable antique radio.
If you’re interested, leave a comment! Pricing is expected to be $3-5 per capacitor depending on type and value.
I was lucky enough to get to work on a beautiful example of this 1954 Philips 778-2 radio. This is a rare, very high end, excellent piece of history which deserved to be taken care of. Very little information is available for it that I’ve been able to find other than a schematic which was published in the Radio College of Canada service manual series; even the Radio Museum doesn’t seem to have an entry for it, which I’ll have to correct in the near future. It looks great, too, in a massive cabinet weighing at least a hundred pounds.
Interestingly enough, this radio is AM only whereas you’d find a similar radio from the U.S. with FM from the same year. As I was told, FM radio hadn’t yet made it into Canada due to licensing issues; that lagged a few years behind the United States. If anyone has more information on that topic, I’d love to hear about it. There’s also a name plate on the top indicating this particular cabinet was custom-built for a certain wealthy Toronto family. As you pull the front panel down to reveal the tuner and record player, the top is attached to a linkage and slides back similar to how a piano might open.
Definitely a very rare pierce here.
With 14 tubes, including four 6V6s in parallel push-pull, this is a great performer. The transformer (a 25-Cycle model) is absolutely massive, too, and the entire chassis itself is thick stamped steel. This is built like a tank and very serviceable.
It used a very interesting linkage to control the position of the dial band indicator:
This radio was serviced once before in the modern era in Toronto, and there was some evidence of previous repairs. It still had most of the paper, and primitive ceramic disc capacitors which were still mostly wax coated and are generally suspect at this point in time. The shop which did the repairs left a lot of old components in place, only replacing a few. This definitely isn’t the standard of workmanship I hold myself to, and in general it’s a poor practice – paper and foil capacitors and early disc capacitors are about 50 years past their working life at this point and even they “work”, they’re not working as well as they should. All it took was being moved to cause something left in place to fail.
This radio was serviced a few times back in the day, and then recently by that shop in Toronto.
The resistors were all specified as precision types, and by some miracle, only a handful of resistors were outside their marked tolerance. The most drifted were the cathode bias resistors on the 6V6s which I replaced with precision metal film resistors.
There are a lot of large-value capacitors in this radio, which are fed by a pair of 6AX5s wired in parallel. Plenty of B+ current to go around. Based on my experience with this radio, I’ve added 68 uF and 100 uF to my stock, but during this repair I had to create those high values by adding 10s, 22s and 47s in parallel.
Four filter capacitors and the output cathode bypass capacitor in total: 5 very large capacitors in 3 cans.
In-progress shot while mounting everything up. The negative tabs of the old can make great mounting points, and in this radio all filter negatives connect directly to chassis.
I’ve mounted a couple of terminal strips to hold replacement filter capacitors.
I use red alligator clips to identify where to clip the wires to the right length and solder while relocating the capacitors to the new terminal strips. This was good for helping figure out lead dress of all the wires at once, without losing my place.
The coils and tubes all checked out during earlier testing, so with component replacement complete, I replaced the power cord with a new polarized model switching the hot side, and substituted a bench speaker on the output transformer. For this radio, I made a house call to remove the chassis assembly from the cabinet, since otherwise it would have been impossible to repair.
Finally, it was time for the first power-up! No smoke! I run the first power-up without the rectifier to guard against any obvious shorts, but the second power-up with the radio fully energized worked perfectly!
With component replacement settled, it was time to reinstall the radio onto the chassis assembly and do some listening tests to make sure everything was operating normally. The shop in Toronto added a line input/output across the volume control; I hooked this up to my phone playing Pandora to exercise that functionality. The sound was very, very good when hooked to my test speaker. Very warm and rich tone, and the separate treble and bass tone controls provide a good range of adjustment. The low-end isn’t quite up to modern standards, but as this amplifier predates “true” hi-fi designs by just a little bit, there’s a little weakness on the low end. This is almost entirely due to the output transformer’s size. You simply need a lot of iron to have good low-frequency bass response, and that gets large, heavy, and expensive quickly.
For comparison, an Edcor transformer for the same power rating flat 20~20K Hz weighs 4.5 lbs. and costs nearly $60 by itself. That’s what I’d spec if the original transformer was bad.
When mounting the chassis back to the board with the dial, it was important to get everything to line up.
I’m using a test adapter on the first alignment step, which involves injecting a signal into the IF amplifier grid.
The 455 kHz IF signal is coupled through a 0.05 uF capacitor, which runs very close to the IF transformer itself and so I insulated it with a sheet of paper.
I’m using my scope to watch the RF input (yellow, top) and demodulated audio at the speaker (blue, bottom). My EICO 324 signal generator is pretty unstable when measured with such precision, but it’s similar to what was used at the time and so is entirely suitable for this kind of work.
In this case, the generator’s internal modulation on this setting looks to be nominally 400 Hz. That’s reasonable. The top is the AM RF envelope; both are synchronized and it’s easy to see how the shape of the two waves corresponds.
Zooming in to verify the frequency of an RF alignment point and the level before switching back to watch the audio. That 400 Hz tone is encoded on the 570 kHz AM carrier.
The alignment was positive! Some components inevitably drift with this much age so it’s tough to get spot-on perfect (not to mention, rarely being that good when new anyway). This one is pretty accurate, though, with the dial tracking within one division of the scale (20ish KHz generally). The offset is slightly varied across the dial. This is often caused by permanent changes to coils – coil forms may change size and the coil’s inductance; temperature-compensated capacitors may be subject to drift. That sort of thing. It’s normal for a radio to have a bit of variability in it these days, although when new they were a little bit tighter. Modern radios use self-calibrating phase locked loops in place of L-C tank circuits.
With a 15′ foot wire antenna strung up, it has good tone on the loud music and talk stations. There’s just a few problems with hum that are resisting efforts to take them out, though. Below a certain volume, there’s a loud 120Hz hum and also a bit of buzzing. In a low-interference environment it’s not too bad (nearly normal-sounding, even) but in a more electrically noisy environment it turned out to be a major problem! Back to the shop for more investigations. One important lesson is that my bench speaker is much less efficient than the speaker this radio came with. The hum was much louder when installed with the original speaker.
By looking at the schematic, this is really a nice-but-pretty-well-settled-technology radio receiver coupled to a very high-end mono amplifier. There are 16 tubes total; 2 are the rectifier and 1 the tuning eye, leaving 13 working tubes. The radio receiving tubes (6SG7, 6SA7, 6SK7 and 6AL5) are the RF amplifier, converter, IF amplifier and detector. That leaves a full 9 for the audio amplifier: Five voltage amplifiers and driver tubes driving a full set of four 6V6 tubes. On a hunch, I started pulling AF tubes. At the time this was to check for issues with the shielding, but one stopped me: the schematic calls out five 6AT6 tubes, but I ended up pulling four 6AT6 tubes and one single 6AV6 in the first AF amplifier position.
They’re fairly similar tubes, with a key difference: the 6AT6 has a gain of 70, while the 6AV6 has a gain of 100. In practice, the 6AV6 is 30x more sensitive than the tube the circuit was designed for – and as a result, it was picking up interference the circuit as designed wasn’t sensitive to. This would have had follow-on effects, too: with the first position introducing the interference, every tube afterwards would amplify the bad signal with the good. Luckily enough I happened to have a single 6AT6 in stock to replace the incorrect tube and this radio began playing perfectly hum free as soon as it warmed up. Problem solved!
I’d speculate tube was replaced with an incorrect substitute last service, but we’ll never really know how that happened.
Now time to deliver it for real – reinstallation back in the cabinet:
Fully serviced, this radio will continue to play faithfully for many years to come! It’ll be able to keep up with the times, too, since it’s been retrofit with a standard audio connector – it would be perfect with a Roku or other Internet radio hooked up permanently! This was a great project. I love working on these top-of-the-line sets, seeing how they’ve been treated in the past, and how they’re being used in their homes – very few of these exist anymore, and I’m lucky to have had the opportunity to work on this one.
I got this Bose 901 Series II equalizer in for repair recently and have finally had a chance to send it back out! It’s going back to its home on the East Coast to be the centerpiece of a Bose 901 Series II system that’s being brought back to life.
This one arrived in what looks to be all original condition.
It’s showing its age, though. The filter capacitors have started to leak visibly. The seals on the ends of the electrolytic capacitors can wear out with age and let the electrolyte out and moisture in, which will lead to failure.
The smaller filters, and output capacitors, look like they’re starting to seep a little bit as well.
I set about replacing the capacitors as is standard on all of my repairs; I tested the pulls to see some of their health.
I also replaced the film capacitors with brand new units:
It’s time to test the transistors; I’d hate to get further down the line. The same multi-tester has mini-grabbers which are perfect for gripping the transistor legs in circuit.
This tester automatically identifies ECB and characteristics; I’m checking to make sure they’re all showing about the same.
Next up, replacing the resistors with precision, low-noise metal film models.
I tested some of the replaced resistors, too. I’ve seen as bad as +35% in other Bose 901 equalizers. The Series I seem to have the worst drift, but this Series II had some significant drifting as well. Drifted resistors can throw off the carefully designed equalizer curves and keep the 901 system from reaching its potential.
As it turned out, the neon indicator lamp had also burned out – the metal-glass interface where the leads exit the envelope frequently gets loose and the neon leaks out over time. Unfortunately, a camera mishap deleted the “pre” photos of the replacement process. The neon lamp and leads can introduce interference; at the time these were invented, LEDs weren’t available but a low power, low heat light source was required. To get around this, Bose used aluminum shielding tape over the light. I removed this tape, slid the housing off, removed and replaced the NE-2A neon bulb, coiled up the leads, reattached the bulb in its housing and placed it back on the panel.
This did, as expected, produce interference – so it was time for replacing the shielding. I opted for copper shielding tape; this is commonly available and is period-correct (in fact, the power transformer is already shielded with copper shielding tape from the factory.) I shielded the entire length of the leads as well, so there’s a bit larger. This tape is both solderable and has a conductive acrylic adhesive for a variety of shielding options.
All in all, it’s looking pretty good – and burn-in testing with my set of 901 speakers proved it sounds great, too!
This equalizer will return home for many more years of faithful service! One more back to its full potential, but there’s plenty more out there to fix.
I generally write about the 901 Series I equalizers which come into my shop for repair. That’s natural – the Series I is the oldest, and as such, its components are most likely to have failed. Series II, III and IV are all getting up to that age, though, with a tapering failure rate as you head towards newer technology. The Bose 901 Series I and 901 Series II Active Equalizers are substantially similar: in fact they can even be interchangeably used with either Series I or II speaker sets, as both models use the same curves. The main changes are some modifications to the power supply, and an improved equalizer network which eliminates the 22mH inductors in favor of some different resistors. With a few years advances in electrical engineering, Bose was able to slightly reduce the parts count.
Some differences should be immediately obvious. One of the 100 uF capacitors has been replaced with a 500 uF capacitor; there are two fewer signal capacitors, no inductors, a prominent ceramic cap across the AC input for additional noise elimination, shielding around the transformer and neon bulb, and the notable lack of a power switch. The Bose 901 Series II equalizer is designed to be connected to the switched outlet of your hi-fi stereo receiver or amplifier and have its power controlled from the single switch.
Otherwise, it uses similar carbon composition resistors which drift with age and conditions. In this case, about a quarter of the resistors I tested were exceeding their marked tolerance. Many repair services for the Bose 901 Series I and Series II equalizer only focus on capacitor replacement (or even worse, only on electrolytic capacitor replacement) and leave resistors outside their tolerances alone, which can change the curve applied by the equalizer and result in sub-optimal performance.
Replacement is quite straightforward. De-solder the old components to de-populate the board, replace the components, re-solder. In this case, I moved through the process in a couple of stages when I found time to work on the equalizer. There are around 80 parts to replace , it is fairly time-consuming.
I have an inexpensive but accurate digital multi-testser which can evaluate and auto-detect diode, FET and transistor characteristics as well as measure capacitance, inductance, ESR, and loss of various components. I applied it to some of the removed capacitors, which were very clearly dead:
This one is supposed to measure 5 uF – which is the equivalent of 5,000,000 pF. Its actual value less than 1/20,000 of its expected value. That’s not good for that output channel!
Another output capacitor didn’t fare much better.
And same for a power supply capacitor, measuring lossy with high ESR and registering capacitance of only 7.9 uF when it should read 100 uF. Bad power filtering in a hi-fi system is a guarantee of bad sound! Fortunately, replacing the tired parts will fix everything.
This Bose 901 Series II equalizer returned to its home and hi-fi, and after this complete overhaul, will continue to serve faithfully producing beautiful sound for many years to come.
My workbench has been absolutely swamped lately, so I’ve been rather slow on writing up the projects I finish. I’ve finally had a little bit of time to put some of this down on paper and the first thing cleared off the bench is a Bose 901 Series I equalizer, serial number 31131 brought back to life!
The set’s owner reported it was giving him noise and distortion and definitely needed to be serviced. That’s pretty standard with these Series 1 equalizers, and many Series 2 – the parts are just so old they degrade and fail and can’t deliver the kind of performance the Bose 901 Series 1 speakers deserve. He also requested I update the RCA jacks, as the old style jacks were spaced too closely together to support the high quality Monster cables.
This one came to me with some evidence of having been repaired at least twice over its lifetime. One of the 100 uF electrolytic capacitors was replaced, as were the two 500 uF primary filters. The two replacement main filters were actually a bit of an upgrade and were much newer, doubled capacity at 1000 uF each which will slightly lower the noise floor even further and provide better quality power.
It’s very easy to see with the original set of capacitors where the problem lies. The red capacitors are very clearly discolored, and spot-checking the resistors revealed they were badly drifted as well. Definitely time for a complete overhual.
Attention to detail and precision are key in refurbishing a 901 Equalizer. There are over 80 components which need to be replaced to restore the unit to complete functionality.
Finally, it was time for burn-in and listening test! I hooked this up to my Series 2 speakers. The Series 1 and 2 equalizers and speakers are compatible, so this provides a perfect live test. My listening lab is in transition right now, so I’m using them on a temporary setup but they still sound absolutely amazing.
After several hours of burn-in testing to ensure solid operation. I was satisfied this one was back to perfect shape. It’s actually in one of the best condition equalizers I’ve had the pleasure of working on – an exceptionally low noise floor, and perfectly operational switches. This one will really make the 901 speakers it’s attached to really sing.
If you need your Bose 901 Series 1, 2, 3 or 4 equalizer repaired, I can take care of that back to meeting or exceeding its factory specifications with precision manufactured components. Click through for more details!
I’ve had the privilege of working on this 1931 Westinghouse grandfather clock radio, the Columaire WR-8. These are a very beautiful and desirable early piece of radio engineering and featured a New Haven Westinghouse electric clock in the front and the controls on the right side of the radio.
This is a nice high-end superhet radio with 9 tubes, 24 24 27 24 24 27 45 45 80. Push-pull 45s will give a great warm sound out of the 12″ speaker mounted at the top of the clock. It’s definitely worth fixing up – the Radio Collector’s Dictionary lists its value at $900, although they go for somewhat less than that in the wild. This is a very early design and everything was still very large – not to mention, the radio has a 4-gang tuning capacitor. The power supply is full of large iron. Put together, the radio has two chassis each larger than most even large radio chassis even a few years later.
Underneath, it’s a fairly straightforward layout. Coils, IF transformers and components. The capacitors are all in large blocks against the chassis.
In the power supply, there’s some immediate bad news:
It looks like the power supply filter capacitors failed and shorted out, causing excessive B+ current draw which caused damage and internal fusing, and the heating caused the transformer’s potting tar to melt out all over the bottom of the chassis pan. The B+ winding is supposed to show about 350 Ohms when in good condition, but it was showing nearly a dead short. I set about locating a replacement transformer in the background and worked on some other aspects of the repair.
Fortunately, there are quite a few models which used a similar power supply. Quite a few Victor radios of the era, several models of Radiola, and the other Westinghouse radios all had identical power supply chassis with parts that could be used interchangeably.
The capacitor block in the chassis was up for replacement. I first thought about mounting the replacement terminal strips on the underside but chose to move them for final installation.
The detector plate RF choke was open, so I mounted up another terminal strip and replacement. The value isn’t especially critical; I used a 10 uH plate choke with negligible DC resistance and rated for 2A, an order of magnitude more than it will ever experience.
Quite a few weeks later, the replacement transformer did turn up. It’s a period service upgrade transformer. RCA specified a separate winding for the 45 tubes which reduces hum, so this new model connects the thickest 2.5V winding to the receiver chassis terminals, and the thinner 2.5V winding goes to the #45 output tubes. This isolates the . Even though this does reduce the hum level somewhat there is still some baseline hum due to the primitive filtering techniques of the day.
The filter and bypass capacitors are also in a block. I used terminal strips with mounting feet and soldered the feet to the existing mounting tabs to provide a secure mechanical connection but no electrical connection. Then I mounted replacement capacitors and components to those terminal strips.
With the electrical replacements finished, it was time to set up for a test power-up.
The dial indicator lamp had split apart. I had a replacement on hand, but it mounts up a bit differently, so ended up having to wrap the mounting hardware with insulating tape as one part of the mounting tab is electrically engaged on the new one.
First power-up went without incident and I set about for an alignment!
My camera’s memory card was corrupt and I lost a bunch of photos of the reassembly process which is really unfortunate. I’m hoping my client sends me a photo of the radio installed in their home so I can have one to show off for the collection. This radio was large, heavy, and local so I delivered it to its final home and helped with the installation in testing – even in a known radio dead zone, it managed to receive a few AM stations with a short length of random wire antenna and with a proper receiving setup it should be a very high performing radio.
I’m working on a 1930/31 Westinghouse WR-8 Columnaire clock-radio which had a bad transformer. The filter capacitors failed and shorted the high-voltage secondary, burning it open and causing a lot of heat and melting.
The replacement is a General Electric service transformer from a Radiola 82, which shared the same chassis. Production revisions led to an improved design over the original, with a separate 2.5V winding for the #45 output tubes to reduce hum and the rest of the RF tubes on their own independent 2.5V winding, so the new transformer will offer a noticeable performance advantage over the original, too!
Recently, I took in a beautiful Philco 66B for repair. Manufactured in 1934, this chassis ended up in several different models – a couple of tombstones, a cathedral, and at least two console radios. They’re all 5-tube radios with the AM Broadcast Band and 1 Shortwave band.
Philco’s designs spanned the entire range of quality, with entry level sets being subject to various interesting design quirks of junior engineers and more advanced sets designed with tight tolerances. They did tend to use potted components longer than most other manufacturers that I’ve worked on, though, and that coupled with quite a few other issues made this one of the most challenging repairs I’ve completed with a lot of unexpected detective work.
The tube line-up of 6A7 78 75 42 80 is very common. The 78 tube is effectively identical to the 6D6 tube, although they were developed separately. After testing, this radio needed a new 6A7, 78 and 75 tube which I replaced from my stock. A few spiders once lived inside but were clearly long since gone and were vacuumed out easily.
Something happened to the speaker at least twice in the past. There’s glue, and two different types of tape applied to the cone.
The underside looked untouched, or was serviced only at an authorized Philco retailer which replaced with branded components. I couldn’t say for sure.
This model did have a terminal strip, stacking components in two layers. I had to disconnect a lot of wires to remove it to get at the connections below.
I replaced out of tolerance resistors and capacitors as normal, including the molded bakelite capacitors which I replaced with terminal strips and discrete capacitors. It would have been much easier to work on if Philco had switched to cardboard capacitors for all parts instead of only some.
Time for reassembly.
The first power-up was a success! In the sense that nothing caught on fire, but it wasn’t making any noise – even when probing various circuit points listening for activity from the speaker. I spent quite a few hours troubleshooting and it turned out to be quite a few very subtle problems which only turned up after a lot of diagnostics. Each resolved problem revealed something new.
All the coils checked out, and initial checks revealed voltage all the places I expected it.
As it happened, I accidentally flicked off the power strip with the workbench light instead of the strip with the radio on it, and glanced down in the dark at the tubes to see a bright blue glow in the #42 output tube. That was the first failure. It wasn’t readily visible in the black getter tube under bright lighting, and the tube tested good on the first pass. It must have finally given up during the time it was powered on for troubleshooting. I replaced it with one from stock, and was able to get a few clicks and some minor static, but nothing significant. On a hunch I tested the resistance from various points in circuit to ground, and quite a few had drifted – but the resistors had been replaced! In other cases, the end of a capacitor to ground was several hundred ohms. The 1934 solder joints seemed to have failed. After I tightened down my new grounds and re-soldered others, the resistance was fixed, but it still wasn’t making noise.
I removed a test jumper but noticed I wasn’t getting the right voltages, and it turned out now the #75 detector didn’t have plate voltage. Due to an error on the schematic from the draftsman in 1934, the capacitor’s connection to B+ was omitted.
In green, I’ve highlighted the path B+ (high voltage) is supposed to flow from the rectifier cathode to the plate of the first audio amplifier. It’s a very straightforward path…if the draftsman had indicated that tube was supposed to be connected to the power supply. In red, I’ve indicated a missing connection symbol. Without it, there was no power being supplied to the first tube in the audio amplifier stage and the audio signal was being killed at that point before it could make it to the final output amplifier. Using an alligator clip, I restored that connection to test, and the radio sprang to life making noise on the next power-up.
The second filter capacitor should have been connected to both B+ and to the plate path for the #75 tube, rather than just the plate path. (Incidentally, the two capacitors are both at the same potential, so under the correct connection scheme could have been replaced with a single capacitor of a larger value.)
With the jumper back in place, the radio powered up and immediately tuned static across the range and it was on to final tweaks. This radio is very susceptible to interference even with the shield in place, but it picked up stations immediately with a 3′ antenna although some were weaker than others. I hooked up my signal generator and oscilloscope.
The Philco 66 uses a 460 kHz IF, so a nominal frequency of 458.7 kHz is close enough. The signal generator is from the 1950s, and even though it’s been reconditioned, it’s just not very stable – the frequency randomly fluctuated on either side of the center. I’d like to get a synthesized signal generator at some point. This was the same equipment that would’ve been in use at the time (or better), so it’s perfectly suitable for alignment.
Somehow this Philco managed to keep its metal plugs to prevent accidental adjustment to the IF trimmers. I went through the alignment and peaked the dial at the appropriate locations. Then, everything went back together:
This model of Philco went through quite a few design revisions over its lifetime, which complicated the repair efforts – each variation had slightly different arrangements to defeat interference this model was very vulnerable to. Even perfectly repaired, this radio showed sensitivity even to switching on and off a work lamp near-by and feedback from ambient electronic noise. That’s just the reality of modern electronics life – there wasn’t the same kind of EM spectrum pollution back then there is now, and antique radios often just don’t have the ability to reject interference the way modern electronics do.
Even with the possibility of interference, this Philco came back to life beautifully and tuned across the entire range of AM broadcast stations, perfect for listening to Oldies or the Mariners’ game.