Restoring a Supreme Model 562 Audolyzer

This Audolyzer has a black front panel and is S/N 619, making it older than my gray model S/N 2443 from circa 1946. My best guess at a date is the early 1940's. Maybe I can find something inside that will narrow it down.

I hadn't planned to buy another Audolyzer but the price was right and it is the perfect match to both my 560A Vedolyzer and my model 561 Combination AF and RF Metered Generator. I can use them together as a "dynamic analysis system" just as in Supreme's 1941 advertisement.
The front panel is in decent shape and looks to be covered in the usual cigarette smoke residue. Somebody smoked a lot around this thing.
A side view. Unlike my gray Audolyzer, this one looks to be all original and I don't see anything missing. Looks like even the probe cable can be cleaned up and reused.
The cabinet is sound but definitely needs refinished. The original finish was just lacquered blonde oak, but after it is stripped and sanded, it will be stained in golden oak, and then sprayed with clear satin enamel.
The original rear panel and tag are still there and in good condition. It seems to be pretty common for the back to go missing on these. I also took a peak inside and the chassis looks to be in good shape too.
The chassis is covered in dirt and dust, as thick as a blanket. But underneath it all, the paint still looks like it's in good shape. This Audolyzer chassis has a black wrinkled paint finish just like my model 563 audio generator.

​I had a bit of an accident with a cleaner which caused a little paint loss in one place on the chassis, since touched up, but in the process discovered that this chassis is actually chromed and matches the chassis in my Vedolyzer and Combination AF and RF Generator. It was just painted over at the factory. This is another reason I think this set is from earlier in the 40's, because my later gray Audolyzer chassis is definitely not chrome underneath. I wish they hadn't painted it.
Under the chassis is clean and looks original. There is what looks like cadmium oxidation on the metal of the power supply filter choke, but no rust on the chassis.

​I see there is a bias battery in the first audio amp and a #80 rectifier tube that match the older Audolyzer schematic, but there are also front panel functions, the ohmmeter and the Audio Input/Scope jack, that match the later schematic. More of Supreme's continuous design changes.
Someone in more recent times foolishly tried to power up the Audolyzer without checking for bad capacitors first. This huge puddle of wax is from the box containing the three power supply filter capacitors. And since there are at least two layers of wax, they did it more than once. There's also some paper and foil capacitors that have dripped wax, too. To make sure they didn't damage any expensive parts in the set, I checked the primary of the audio output transformer, the speaker's field coil, the filter choke and the power transformer for opens and shorts. The 1946 schematic has resistance readings for all the windings, and all except the power transformer high voltage winding are spot on the ohms values given.
​The power transformer high voltage winding is shown as 600Ω, but is reading 530Ω, and there is 14Ω difference in readings between the center tap and the two ends of the coil. This doesn't necessarily mean the transformer is bad, but it doesn't prove it's good either. So I temporarily powered it up on my variac (with no tubes installed in the Audolyzer) and checked the AC voltage readings. They look good, with less than a volt variance from the winding center tap to both sides, and the filament voltages look good, too.
Someone in the past actually wrapped the batteries, which helped prevent them from rusting the chassis. That was thoughtful.

​Hmmm, I wonder what all the white spots are in the dust? Probably not something I'd want to breathe in.
The front panel was removed to straighten a slightly bent corner and clean off the yellow crud on it, as well as make it easier to clean up the chassis. In the photo the left side has been cleaned but not all of the right side. After cleaning it will be polished and waxed.
The shielded multiplier has a couple of paper and foil capacitors that need replaced. The original, older Audolyzer schematic has three capacitors in the multiplier, but the later schematic only has two, as in this instrument.

​These shielded cans can be stuck together pretty tightly. In my model 561 Generator someone really bent up the edges of the back half of the shield can trying to pry it open. The easiest way I've found to open them is to carefully run my swiss army knife blade around the joint between the two halves. It loosens them enough that the halves pop right open.
Inside the multiplier shield is an interesting tidbit. It's a disc cut from a larger panel and looks like it might have been an advertising sign or something similar. This is a steel plate and not aluminum like the Audolyzer panel. After looking at some Supreme catalogs and their logo I think it might possibly have said something like:
SUPREME
RADIO TEST INSTRUMENTS
​Supreme by Comparison
Or something like that. Their catalogs and ads used the phrase "Testing Instruments", but it's pretty obvious in this case the plate just said "Test". They also used the phrase "Radio Testing Instruments" on their 1940 catalog cover. Maybe that's why it got cut up into little discs, somebody messed up the spelling. Anyway, just a little Supreme puzzle to ponder.
Under the chassis is done. All the old electrolytic and paper and foil capacitors were replaced, but a lot of the original resistors were still very close to their marked values and were left. The hardest capacitors and resistors to get at are in the shielded box for the two RF amplifiers. The old filter capacitors were removed from their silver cardboard box and the new filter caps put back in it to keep things looking original. I also flipped the box around so the label is visible. Also, in the upper right corner of the chassis I added an inline AC fuseholder with a 1-amp fuse for safety.

​The old 1.25-volt button bias battery has been replaced with a modern 1.5-volt button cell for testing. I pressed small indentations in both sides of the battery so it would stay clipped in the holder. If it doesn't work then the audio circuit will be modified to match the later Audolyzer schematic that provides self-bias.
The top side of the chassis is also finished. All the tubes were tested and I replaced the glass 6SQ7 tube with a metal tube to eliminate the cobbled up tube shield someone had put over it.

​I haven't replaced any of the range resistors for the volt and ohm meters just yet. I'm waiting to see how close the readings are before deciding if any really need changed.
The front panel is finished and all the knobs cleaned and polished. The two tip jacks for the meter were replaced with matching style banana jacks because all my meter leads are banana plugs. Also, I did change the positive side to a red jack. All the old corroded panel nuts were also replaced. Other than that the rest of the front panel is original.

​I cleaned and polished the stress relief spring on the input probe and reused the big, thick original probe cable and tip. I couldn't find any cable that came close to duplicating the look of the old cable, and thankfully it was still in decent condition. I did have to change out the screw-on alligator clip, as well as the out of tolerance 100KΩ internal probe resistor.
A summary of parts replaced so far includes 4 electrolytics, 24 paper capacitors, 8 resistors, all the old panel nuts and nuts for most of the 6-32 screws, a few grommets, the rubber cabinet feet, the bias and ohmmeter batteries, and the antenna input cable.
First power up went well. I brought up the TRF receiver by switching to AF Output mode, and picked up the local AM station right on frequency with just my finger as an antenna. I'm not having any sensitivity problems like I did with the gray Audolyzer and I suspect it's because I used shielded microphone cable instead of 50Ω coax for the input lead. The voltmeter works and I set it on RF to use as the TRF's tuning meter. I set the Variac for 117.5VAC as specified on the 562's rear panel label and the B+ is spot on at 270VDC. The filament voltage is running about 6.6VAC. And I took a look at the audio out of the first AF amp (in the 6SQ7) and it looks clean and undistorted, so the 1.5-volt bias cell seems to work just fine. So far so good...
More to come...
Page created 10/8/2021
Last edited 6/25/2022