[R-390] R390A AGC troubles

[Jim Miller]

Another thought:  The antenna trimmer control shaft and gears are at AGC 
potential in the RF stage.  The phenolic gears and washers insulate the 
shaft from ground.  If someone over-lubricated the antenna trim gears, the 
lubrication oil could be forming a path to ground and shunting the AGC in 
the RF stage, which could create overload or poor AGC action.  The shaft and 
gears need to be purged with a chemical cleaner like Big Bath to rid them of 
any oil.

----- Original Message ----- 
From: "Bill Coleman N2BC" <n2bc at stny.rr.com>
To: "Dennis Wade" <sacramento.cyclist at gmail.com>; <R-390 at mailman.qth.net>
Sent: Wednesday, July 27, 2005 6:31 PM
Subject: Re: [R-390] R390A AGC troubles


> Hi Dennis, it was my understanding that zero input signal state is 
> around -7V.
>
> The other measurement that is 'wrong' is the suppressor grid voltage on 
> V504 & V508), it is +3.4V, should be -2.5V.
>
> The voltage on the grids of the IF strip is consistent with the -0.5V.
>
> Externally, it sounds like minor overloading on strong signals.
>
> THX, Bill
>
> ----- Original Message ----- 
> From: "Dennis Wade" <sacramento.cyclist at gmail.com>
> To: <R-390 at mailman.qth.net>
> Sent: Wednesday, July 27, 2005 6:11 PM
> Subject: Re: [R-390] R390A AGC troubles
>
>
> I'm at work, but I don't recall that -0.5V zero signal on the AGC bus
> was a problem.  When I finally got mine fixed (different problem
> though, see previous posts) the small + zero signal voltage I had been
> seeing became -0.4V.
>
> What are the grids of V%01, 502 and 503 doing?  What do you "hear" in
> terms of symtoms..how does the radio sound under various signal
> conditions?
>
> Dennis
>
> On 7/26/05, Llgpt at aol.com <Llgpt at aol.com> wrote:
>>
>> It is quite possible the "cadaver" Z-503 is a bad one too. They are a 
>> known
>> troublesome part. If possible try a known good if deck. Maybe you have a
>> friend  close by.
>>
>> Les Locklear
>>
>>
>> In a message dated 7/26/2005 2:47:01 PM Central Daylight Time,
>> n2bc at stny.rr.com writes:
>>
>> Along  the way I managed to destroy Z503 so I pulled one out of a 
>> 'cadaver'
>> IF  strip.  I noted that it's slug is fairly well centered in the core.
>> Upon
>> replacing Z503, the 'new' one behaved the same way.... increasing  stage
>> output as the slug was cranked toward the top but it runs out of 
>> adjustment
>> before peaking.
>>
>>
>>
>>
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>
>
> -- 
> Dennis L. Wade
> KG6ZI
> Carmichael, CA
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