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 Quiet RCA 143

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DrewT



Posts : 2
Join date : 2010-10-12

PostSubject: Quiet RCA 143   Tue Oct 12, 2010 3:59 pm

Hi , I am taking a break from some othe projects that are baffeling me. So I decided to go back to this radio. I have a RCA 143 I restore several years ago. Looks great dosent play great. Gets plenty of stations and is clear, except for a heavy tone and low volume . Even with the volume all the way up , it is just barely loud enough to hear. All caps are replace, all necessary resitors change. I check the tubes again, they are fine. I check the readings of the speaker and they match the schematic.
What could be keeping this radio from its full potential ??

thanks

Drew
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Johnnysan



Posts : 64
Join date : 2010-10-12

PostSubject: Re: Quiet RCA 143   Tue Oct 12, 2010 4:51 pm

Possible bad speaker. Was it aligned at 460kHz? If it were aligned at 456 or 455 it would affect operation.
This radio uses push-pull 42s; the driver transformer (T2) may be at fault.
What do you mean by 'heavy tone'? Is it generating an audio oscillation?
I think the B+ at the output plates should be about 300; is this correct?
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tubes4life



Posts : 33
Join date : 2010-10-12
Location : northern Florida

PostSubject: Re: Quiet RCA 143   Tue Oct 12, 2010 6:50 pm

I'd start by checking voltages in the power supply/output stages, and comparing them to what's on the schematic.
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DrewT



Posts : 2
Join date : 2010-10-12

PostSubject: Re: Quiet RCA 143   Tue Oct 12, 2010 7:42 pm

Hi, Thanks for the replies. I think I found the problem. Two new resistors were way out of resistance . i replace them and much better.
I would like to try to align it. When they say connect to the grid of the 1stdet , does that mean pin 3 of the 6a7. ?

thanks drew
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jack shirley



Posts : 67
Join date : 2010-10-12
Location : SE USA

PostSubject: Re: Quiet RCA 143   Tue Oct 12, 2010 7:44 pm

Johnnysan wrote:
Was it aligned at 460kHz? If it were aligned at 456 or 455 it would affect operation.

I don't think that would make it "barely loud enough to hear".
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marcc

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Posts : 30
Join date : 2010-10-12
Location : Victoria, Australia

PostSubject: Re: Quiet RCA 143   Wed Oct 13, 2010 3:41 am

No... The control grid is 5. Use around a 200pf cap in series with the sig gen. and hook it to the top cap. You check the last IF first. Don't wind it up full.

Some radio's actually have a description of how to align them

Marc
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