Unknown audio transformer.

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Unknown audio transformer.

Post by cameronw on Sun Dec 17, 2017 1:44 am

I recently bought a 1959 Olympic Radio Model Number 457 WH-Q-S off of ebay stating that the electrolytic caps were replaced. When it arrived it worked great for about 30 minutes then it stopped with no sound at all. I soon replaced the non electrolytic caps and nothing happened. I then replaced the tubes and still nothing. Tubes glow and everything looks okay but no sound at all. I tried to find the manual or anything but no luck. I am new but I believe now its the audio transformer. The transformer has only "138-130" on top and that's it. I am hoping to see if its possible to find a replacement. Thanks for the help!

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Re: Unknown audio transformer.

Post by Chas on Mon Dec 18, 2017 10:41 am

Go to this site to determine how to replace a defective audio output transformer:

http://www.radioremembered.org/outimp.htm

Once the transformer specifications are determined AES or others will have them.

The code numbers identify the manufacturer. The B+ voltage and tube type will determine what transformer is needed.
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Re: Unknown audio transformer.

Post by willy3486 on Mon Dec 18, 2017 1:07 pm

Have you used a signal tracer on the circuit from the tube to the audio transformer to see if there is a signal?

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Re: Unknown audio transformer.

Post by cameronw on Mon Dec 18, 2017 5:03 pm

I have not tried to signal trace because I have zero audio at all. I will certainly try it if I figure it out and get the time too. Thanks

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Re: Unknown audio transformer.

Post by Chas on Mon Dec 18, 2017 5:18 pm

I assumed that your tests proved the audio transformer open.

Turn on the radio, measure with a voltmeter from the B- to the plate pin on the output tube, is there plate voltage at the audio output tube? That will confirm a good primary.
If O.K.
Turn off radio and disconnect from power. lift one lead from the audio transformer secondary and measure resistance from the open lead to the far terminal of the speaker that the other side of the secondary is located. I should measure about 2 or so ohms with an analog meter. From that same, still connected location on the speaker measure the to the soldered terminal of the speaker. It should be about 3-4 ohms with an analog meter.

Do allow for the fact that some radios use the chassis for a circuit to the speaker voice coil, so there will be but one wire and chassis connection to measure both the secondary of the output transformer and the voice coil of the speaker.

Depending what is found, the audio transformer could be bad or the voice coil circuit of the speaker open.

Sometimes the tinsel wire from the speaker terminal(s) will go open so if the speaker circuit is open check the tinsel wires too...

If you have no B+ at all the looking at the power supply is next...

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Re: Unknown audio transformer.

Post by willy3486 on Tue Dec 19, 2017 9:12 am

I am going to give a guess this has some 12au6,12av6,35w4,and 50c5 tubes. So it probably doesn't have a power transformer.So it sounds like the tubes lights up as well. As far as a signal tracer I use a tracer and a signal generator most of the time in repairs. I highly recommend them to people as they can do so much for you quickly. If you haven't done much troubleshooting since it died and haven't narrowed it down to the audio transformer by troubleshooting it could be a issue anywhere. That's why testing the circuit about half way can knock out half the parts as bad. I would get a schematic and use it to troubleshoot as well. If I get the chance in the next few days I will look at my sams and see if I have it.  If you had the schematic you could also check the caps you replaced to see if you made a mistake and put it elsewhere, I have done it and if you do these long enough everyone will. Doublecheck the MF values as well. I had a radio 30 years ago I really liked and couldn't get it going. I dug it out a year or so and traced it to a cap I replaced. It had the correct number 47 but was a different MF. But my guess on yours is a original component failed.

Since it was playing my guess is it had a component that was weak and burned into. It could be anything from the IF transformers,coils,speaker or audio transformer would be my first thoughts.I have seen radios work perfectly then after a few minutes quit due to the wire of a coil or IF transformer break at the point it is soldered to the pin it is on. I usually wrap a thin wire on the pin and then the coil wire. I heat it up and let the solder flow. Then I check with ohmmeter to see if it has continuity.  But without tracing it down to the exact point it will be only a guessing game. If you have time trace the signal from the input of the first IF transformer to the speaker. I think you will find the issue if you do. If you don't have a tracer they can be had cheaply or made from a old transistor radio. I made one from a transistor radio back in the early 80s and its the tool  use the most. There are instructions on the internet.

Keep us informed.

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