[Milsurplus] Re: [Hammarlund] BC-779 Latest Update

[Greg Mijal]

Sounds like you are looking at voltages with a DMM, everything reads higher 
than your old book spec's based on a 20k ohm multimeter or whatever.
The -12.0 volt comment does not compute here.  Grid voltages with avc action 
impressed read not more than a couple of minus volts on my stuff and the 
voltage fluctuates as the signal strength changes.
The only way I have been successful in troubleshooting avc problems is 
tracing out the basic avc system then disconnecting the avc control voltage 
grid by grid until the failed stage is found and I always use an 
oscilloscope to do this with.  It's time consuming cleaning up the mess 
later but it works here.
Hang in there baby!
Greg
WA7LYO
in sunny Feenix
----- Original Message ----- 
From: "Carole White-Connor" <carolew at bellatlantic.net>
Cc: <hammarlund at mailman.qth.net>; <milsurplus at mailman.qth.net>
Sent: Sunday, January 07, 2007 7:07 PM
Subject: Re: [Hammarlund] BC-779 Latest Update


> Not much progress on the AVC problem. I'm giving the voltages. Perhaps 
> this
> will give someone an idea of the problem.
>
> AVC Rectifier (6H6)
>
> In Manual and in AVC, the cathode voltages are -3.2.  That's what the 
> manual
> specifies.
>
> In Manual, the plate voltages are -3.5. The manual says they should 
> be -3.2.
> In AVC, the plate voltages are -12.0. (The manual specifies only voltages 
> in
> Manual mode)
>
> AVC Amp (6SK7)
>
> In Manual and in AVC, the plate voltage is +270 and the screen is +140. 
> (The
> manual says they should be 240 and 110).
>
> In the Manual, the input grid is -3.2. The manual specifies -1.5V.  In 
> AVC, it
> is -12.(The manual specifies only voltages in Manual mode).
>
> In Manual, it actually is starting to sound like a Super Pro. Replacement 
> of
> the out-of-spec resistors and the caps has made a difference. I just 
> pulled
> C-34 out of the T-1 can. It's a Micramold and was leaking like most of 
> them
> do. It was a pain to get to but worth the effort.
>
> As always, thanks for your help. Any insights would be gratefully 
> appreciated.
>
>
>
> Joe Connor
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