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First sign in

Post by Ben Delk on Tue Apr 03, 2012 10:12 am

I am somewhat new to the antique radio world but they ahve fasinated me my whole life. I'm quickly appraoching retirement age and looking for a hobby to past my time. The last real electroniscs class I had, I think Johnson was President, so it has been a while. I think i still have the basic but when the word "fuzzy logic" is spoken, I reply. I have a Zenith console 6S52 someone gave me. I have done antique furniture restoration as a hobby for quite some time so the cabinet repair and refinish was a breeze. The chassis is an issue I have yet to tackle. Also have an RCA Q10 (AA5)on my workbench now. I have recapped and replaced all resistors, tested the tubes. Double checked everything I can think of so I'm looking to a hint in what direction to go. Here's the issue. Turn on the radio and the I have good volume for about 30 second or so and it gradually goes away. After replacing all the the above items I turn on the radio and immediately got a hard loud tapping coming out of the speaker so Iturned it off and replace the multi-section cap (50@150, 30@150, 20@25) with three similar caps (50@160, 30@160, 20@50). As the volume diminishes the 50@160 cap heats up and "pop' she goes. Rect is 35Z5GT and output is 50L6GT. Any thoughts. Here 's my test equipment, heathkit Sig tracer, heathkit sig gen, Fluke bench dmm, fluke hand dmm, tektronics 2213 oscope, TW-11 Superior tube tester, isolation trnfm, variac.

Thanks for the opportunity to learn....this is great site.
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Re: First sign in

Post by Resistance is Futile on Tue Apr 03, 2012 3:07 pm

Sounds like your cap polarity is reversed of what it should be. Also sounds like you have a resistor problem in the B+ as opening due to caps shorting and allowing too much current to flow through the resistor(s). Look at R10 (33 ohms) and R7 (150 ohms) and R9 (1000 ohms)
The clicking or popping could be the resistor(s) opening or shorting from heat. Or you have a short in one of the tubes.
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Re: First sign in

Post by Tony V on Tue Apr 03, 2012 3:54 pm

Welcome to TRF!
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Re: First sign in

Post by Bill Cahill on Tue Apr 03, 2012 8:28 pm

Welcome to TRF. Yes, it sounds as if you have reversed the polarity on the electrolytics.
Probably dammaged resistors. Hope nothing else.
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