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42-1008 power transformer - Printable Version

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42-1008 power transformer - davidff - 08-21-2013

I recently began restoring the chassis on the 42-1008 and found the transformer has an internal short, and needs replacement. The schematic does not give me the voltages, etc needed to find a suitable replacement. Does anyone have any suggestions on where to find one and the voltages needed? I replaced all the electrolytics and a previously blown rectifier, but the transformer gets very hot and has been leaking in the past.

RE: 42-1008 power transformer - Jim Dutridge - 08-21-2013

That depends on which chassis you have. If its just a 42-1008 then the part number is 32-8129 that has 2 seperate filament windings along with the rectifier filament. If its a code 121 or 122 then the transformer was changed to part number 32-8217 and only has 1 filament winding along with the one for the rectifier.

Throwing some numbers together, and figuring that you might have the code 122, I would say secondary of 350-0-350 volts at around 220ma. Rectifer filament 5v @ 2A and the other filament of 6.3v @ 2A minimum. I might be wrong on these figures and I'm sure others will chime in.

RE: 42-1008 power transformer - davidff - 08-26-2013

Thanks for the feedback, I do have the 122 run on my chassis. I purchased a few years ago a transformer with a 400/0/400 tag on it that might work as a replacement. The wires are grouped together, some are green, others are faded red. How can I tell the input from the output? Also, I noticed one is marked with black magic marker, perhaps that is the hot output one? Next issue, should I trace all the existing transformer wires to the rectifier, etc so that I can match them to this transformer? I do not want to ruin my chassis, but my current transformer has to go. Any assistance is appreciated. I can post the new transformer and its wire groupings if that would help.

Thanks,

RE: 42-1008 power transformer - BrendaAnnD - 08-26-2013

Sounds like your transformer has a standard color code. If it does, then it goes like this:

Black/Black-Red: Primary
Red/Red-Yellow/Red: HV secondary (Red-Yellow is tap)
Green/Green: Filaments (may have a Green-Yellow center tap)
Yellow/Yellow: Rectifier filaments

Hope this helps you out.

RE: 42-1008 power transformer - codefox1 - 08-26-2013

Any doubts hook a very low voltage AC supply to one of the thicker (probably green or yellow) windings and measure what comes out of the other windings, and be careful, since they will step up quite nicely! Anyway proportions will most likelyconfirm what has been already said and identify whatever center taps there are for sure. Best.

RE: 42-1008 power transformer - davidff - 09-03-2013

OK, I followed the paths of the wires from the bad transformer as follows:
2 green- filament ones, no issues.
2 black going to the rectifier, seems pretty easy.
1 black going to a 41 output tube pin and 1(yellow?) going to tube 41 also.
1 red to a chassis terminal block -is this a primary?
1 red to the block where the ac lines are attached, is this a primary also?
1 red/black wire to a long bar strip at the top of the chassis.

I am trying to match these to the replacement 400 volt transformer that I have. It also has 9 wires. The primarys are marked so that is fine, the filaments are green and that is fine, there are also 2 yellow ones, I assume this is the rectifier, so that is fine, the area where I am not sure is the 3 other wires grouped together, one has a black magic marker dot marked on it. These are the High voltage wires, I assume.

Any assistance matching these wires would be a great help. The color is faded on all these cloth wires.

RE: 42-1008 power transformer - Eric T - 09-03-2013

Having just finished one of these (the chassis is a couple feet away, let me tell you what you've got:

The 2 greens going to the tube filaments is probably right.

The red wires are the primaries, one goes to a bakelite capacitor block, one to a terminal very close to the bakelite block.

The red/black wire is the center tap of the high voltage secondary, and it goes to a candohm bias resistor (the long strip), assuming it's wired correctly.

There should be 4 wires going from the transformer to the rectifier, and NONE to the 41 audio output tubes. Two of them will be the high voltage secondary legs to the plates of the rectifier, and two will be filament voltage for the rectifier.

Personally, I would mark all the wires, pull the thing out and check the resistance of the windings to verify what wires are what, then figure out a safe way to verify the voltages.

RE: 42-1008 power transformer - Eric T - 09-03-2013

By the way, your bad transformer is not the original.

The original has:
2 white primary wires
2 black filament wires
2 blue rectifier filament wires
2 yellow wires hv to the rectifier plates
1 yellow-green hv center tap wire
2 green wires cut short and taped up.

RE: 42-1008 power transformer - marty - 09-04-2013

Hi All;
Davidff, at this point you could take the Transformer apart and look and see If you can find the short and maybe fix it.. It might be one of the brittle wire(s) that some of the insulation has come off.. It would be no harm, since If you can't fix it, you have not lost anything..
THANK YOU Marty

RE: 42-1008 power transformer - davidff - 09-04-2013

I rechecked all the wires from the transformer, # 32-8129, which is the correct original (run 122) per schematic and per the # engraved on the top of the transformer. There is definitely a wire going to one of the #41 output tubes, and this area has a wire that travels over to a similar pin area on the other 41 tube, but there is only one wire going from the transformer to this area. It appears to be a black wire. The other rectifier wires previously described are correct as Eric described.
Thanks for the input.

RE: 42-1008 power transformer - Eric T - 09-04-2013

Marty has a good point. I pulled off my transformer and replaced the wires coming out of it because the insulation was worn through where it came out of the clamshell. Just take tons of pictures and make notes of exactly where everything connected.

By the way, I'm guessing the wire going to the 41 is either B or ground for the filament circuit. Mine goes to one of the pins of the socket on the rear of the chassis, then over to of the filament pins (the two fat pins) of a 41.

RE: 42-1008 power transformer - davidff - 09-19-2013

Hello everyone. I was able to locate a 40-185 transformer, which is definitely a good unit. It has only 7 wires which appeared as follows when I cut it from the chassis.

1-goes to the on/off switch
1-goes to the "resistor strip area", best I can describe it.
2-go to the #84 rectifier pins
1-goes to the "power block" where the ac connects
1-goes to a tap located between the #84 and the #7c6 tubes, not far from the power block area.

My goal is to connect this to the leads from the 42-1008, which is a somewhat similar chassis with the 2 #41 power output tubes.

I need help matching these up on the 42-1008 as the old transformer had more wires than this(9).

Your help is appreciated. Thank you.