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38-690 puzzle
Ron Ramirez
Silent Key
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Posts: 13,776
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Joined: Sep 2005
City: Ferdinand State, Province, Country: Indiana
#2

08-18-2009, 11:07 AM
This tube is connected as a diode; with the grid acting as a diode "plate".

Very interesting circuit. It is used to control the gain of the bass amp tube (6K7G) in much the same manner as AVC is normally used to control gain of RF and IF tubes, and sometimes mixers as well. A portion of the audio signal is taken from the plate of the audio driver tube (6F6G) and fed to the grid of the bass amp AVC tube, where it is rectified and sent on to the suppressor grid of the bass amp tube. This serves to control the amount of signal amplified by the bass amp tube.

Yes...very interesting indeed.
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Ron Ramirez
Ferdinand IN
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Messages In This Thread
38-690 puzzle - by Guest - 08-18-2009, 10:48 AM
Re: 38-690 puzzle - by Ron Ramirez - 08-18-2009, 11:07 AM
Re: 38-690 puzzle - by Guest - 08-18-2009, 01:19 PM



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  1. The PHILCO Phorum
  2. Philco Radio Discussions
  3. Philco Electronic Restoration