[NJARC] Atwater Kent 82 AVC Volume Problem

[Jim Whartenby]

Greetings George
Have you tried replacing the vacuum tubes?  Beyond testing the tubes on a tube 
tester, actually installing a different tube of the same type, one at a time?
Regards.
Jim



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From: "George B. Shields, Jr." <george-shields at msn.com>
To: NJARC Listserve <njarc at mailman.qth.net>
Sent: Fri, December 30, 2011 10:18:01 AM
Subject: [NJARC] Atwater Kent 82 AVC Volume Problem

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Hi All,
Well, I haven't been this totally flummoxed in quite along time!  I am still 
experiencing a huge amount of trouble with this AK82 volume and AVC control 
problem.  It is a very strange arrangement in which a type 224 tube is used ass 
a "control tube" to regulate both the volume and AVC functionality.  When the 
radio first powers up the volume comes on full blast regardless of position of 
the volume pot, then over the course of about 5 or 6 seconds lowers to a normal 
range.  After anywhere from a few minutes to maybe 15 or 20 minutes the volume 
will begin on its own to fluctuate WILDLY - some times jumping to full volume 
and back way down to the point where you need to turn up the volume pot to maybe 
3/4 the way up and then it will fluctuate between louder and softer on it's own 
and then stabilize for awhile and then begin doing it all over again.  
Frequently, the volume will fluctuate so rapidly it will actually flutter, going 
up and down several times a second!  I have replac
ed the control tube 4 times with no effect.  I have replaced EVERY SINGLE 
resistor and capacitor in the radio excepting for the wirewound resistors.  
There are NO original resistors or caps functional in the set.  Every component 
is precisely on schematic spec. The volume control is original although it has 
been cleaned and measures steady.  I have noted that voltage across the resistor 
network of which the volume control is a part will at times fluctuate as much as 
8-10 volts and I have been unable to figure out why.  The power transformer 
seems fine and gets only slightly warm after playing the set for the better part 
of an hour.
This radio was exhibiting this problem when I bought it.  It had been restored 
by someone else in the past who didd the capacitors but only a few of the 
resistors so of course I immediately replaced all of those remaining nasty 
ceramics.  But none of my work has had any effect whatsoever on this.
Now, my feeling is to disable to AVC functionality of this control tube circuit, 
however the usual tricks of grounding out either the grid or the screen does not 
work. That results in disa ling the volume control entirely with the radio 
playing only at full volume regardless of position of the volume control.  Im at 
a complete loss as to how to disable the AVC and yet retain volume control 
functionality!
The AK82 is notorious for this horrible and screwy volume  / AVC setup and I 
believe it's actually the only AK model out there that employs it, as other 1931 
models did not have an AVC.  

Any of your guys who are way smarter than poor I ever experience this problem?  
What suggestions can be offered to me to disable this AVC and make the radio 
volume stable and controllable??????  Any thoughts will be very much 
appreciated!  I also can shoot over a schematic to anyone who would like to have 
a look at it!
Many thanks guys,-George-
george-shields at msn.com
                          
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