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47-1227 volume problem - Printable Version

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47-1227 volume problem - Guest - 12-14-2008

Im new to this forum, I have a little knowledge about electronics but not alot. Every thing I know is from building a few cnc machines for my shop. I know very little about tubes.. Ron was kind enough to point me in the direction of a manual

I recently aquired my great grandfathers radio. I pluged it in and the fm works however the volume fades as it gets warmer to the point where its barley audible. Does any one know what is likley wrong?

I have read threw a few repairs people have done on these, its seems like they alway start with replacing caps. Why are they so susptable to going bad? What are signs of them being bad?

Thanks for any suggestions

Re: 47-1227 volume problem - codefox1 - 12-14-2008

Of all the components of a vintage radio, the capacitors are the most likely to fail. Moisture and chemistry are the reasons. The electroytic capacitors wil be the first to go, their job is to trap the charge of a positive currant and save it to the next cycle to provide a constant DC voltage to the radio. Next to go are the coupling capacitors which provide DC isolation from one gain stage to another. And finally her are those capacitors which hope to isolate the dangerous "house current" from the metal chassis, which you might accidently touch and thereby electrcute yourself. The rest of 'em might restrict or short circuit the signal to make an otherwise good set inoperative.

My standard procedure is to replace the big eletrolytic capacitors as a matter of course, all the bypass capacitors, and then measure the resistors out of circuit. If the D**n thing still doesen't play, then it's on to more severe diagnostics.

I've Got a 1954 (I think it is a model 432_ GE on my bench that has gone into phase 2 and I have ot a clue so far. But then again, I do have to go to my day job in the morning.

Be careful when working on these old models. Better yet use an isolation transformer.

Re: 47-1227 volume problem - Guest - 12-15-2008

Thanks Codefox..

Can any one make a recomendation on any reading material that might give me a more thourough understanding of how these cool old radios work and the function of there parts. a 101 on tube radios?

Thanks again Codefox

Re: 47-1227 volume problem - Raleigh - 12-29-2008

Elements of Radio Servicing by William Marcus and Alex Levy. c 1947, McGraw-Hill Book Company, Inc. This is a very comprehensive book on the repair of superheterodyne tube radios. Includes a stage-by-stage look at schematics, functions, troubleshooting, and typical problems. Focus is on troubleshooting with minimum test equipment, mainly soldering iron and signal generator. Sections on alignment. Written for servicemen, not engineers, so it is light on theory and math. I found it very readable, with a little concentration. I read it through before I ever tackled a restoration, and still refer to it often.

You can find it in 6 pdf files (a few chapters per file) on this page: http://www.antiqueradios.com/archive.shtml

You might be able to find used copies at used bookstores. That is where I got mine.