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Model 46-420 code 121 AVC
RadioBob
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#1

04-14-2016, 07:55 PM
I am reviving a Philco 46-420 and I have a question about the AVC circuit. In previous restorations I am accustomed to seeing an RC circuit filtering the audio signal off the top of the volume control pot. In this model schematic I find the “R” but not the “C”. Can you instruct me in how the AVC works in this model? Thanks for your help. RadioBob
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klondike98
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#2

04-14-2016, 10:41 PM
Welcome to the Phorum!
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Sorry, can't answer your question but I'm sure one of the crowd here will chime in soon.
Cheers,
Bob
[Image: https://www.dropbox.com/s/5m63ib99yfx2eg....jpg?raw=1]
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RadioBob
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#3

04-14-2016, 10:48 PM
(04-14-2016, 10:41 PM)klondike98 Wrote:  Welcome to the Phorum!
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Sorry, can't answer your question but I'm sure one of the crowd here will chime in soon.

Oops!  Sorry.  I just found the "C".  It was not where I expected it.  It makes sense now.  This is a great forum; I hope to be able to contribute soon.  Thanks.  RadioBob
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Mondial
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#4

04-14-2016, 11:05 PM
In this set, the AVC voltage is obtained from the diode detector through R11 and then filtered by C12. Its a bit unusual in that the voltage is not taken off the detector output to the volume control, but the DC voltage is the same at both points. They also use the other diode of the 7C6 directly across the AVC line, probably to develop contact potential negative voltage to set the no signal grid bias on the RF converter and IF tubes.

http://www.nostalgiaair.org/pagesbymodel...013597.pdf
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RadioBob
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#5

04-15-2016, 10:38 AM
Thank you, Mondial, for the AVC operation description. RadioBob
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  1. The PHILCO Phorum
  2. Philco Radio Discussions
  3. Philco Electronic Restoration