Fw: [R-390] R390A AGC

[Bill Coleman N2BC]

 Thanks Don,  I should have put more info in my original post....

 I have 'lifted' the AGC line at each stage of the IF one at a time
 (disconnecting the appropriate isolation R), the AGC voltage and the
 suppressor grid bus does not change.  Also, measurements in the IF with the
 RF deck disconnected are unchanged.

 I did the 9V battery trick too.  Readings at each of the stages are
 appropriate.

 That's why I keep coming back to the AGC IF AMP, Rectifier and Time 
Constant
 stages.  Z503 will not peak, all other stages peak nicely.  It seems that
 the gain of the AGC IF amp is low because Z503 will not peak.  I suspect 
the
 reduced output is not enough to overcome the positive bias coming from the
 R544/R546/R545 divider string (roughly +17V if I did my Ohms law 
correctly).

 73, Bill  N2BC


> ----- Original Message ----- 
> From: "Don Heywood" <wc4g at knology.net>
> To: "Bill Coleman N2BC" <n2bc at stny.rr.com>
> Sent: Sunday, July 24, 2005 7:47 AM
> Subject: Re: [R-390] R390A AGC
>
>
>> Bill, there is a bunch of AGC information in the below link under IF DECK
>> section. There may be some help there. There is one post that uses a 9V
>> battery on the AGC line to read grid voltages.
>> I had a problem with the R390A RF deck and it turned out to be a shorted
>> Mechicanal Filter input coil.
>>
>> http://www.r-390a.net/Pearls/
>>
>> Good Luck
>> Don WC4G
>> Charleston, SC
>>
>>
>