[Johnson] Valiant I crystal oscillator won't unkey

[Carl]

500K was a standard value under the old system. I dont know what 
boneheaded professor came up with the current system.

Carl
KM1H

----- Original Message ----- 
From: "Paul Carreiro, N6EV" <N6EV at MonteCarloSS.com>
To: <johnson at mailman.qth.net>
Sent: Wednesday, December 17, 2008 3:08 AM
Subject: Re: [Johnson] Valiant I crystal oscillator won't unkey


> At 03:24 PM 12/16/2008, WA5VGO wrote:
>> From the Johnson Service Bulletin:
>>In some cases, very active crystals continue to oscillate under key up 
>>conditions. Increasing the bias on V3 stops even the most active 
>>crystals. Change R7 from 1 megohm to 500K 1/2 watt and R11 from 33K to 
>>100K 1/2 watt.
>>
>>I'm not sure why they would specify a non-standard value like 500K, 
>>but I'm sure a 470K would work fine.
>>
>>73,
>>Darrell, WA5VGO
>
> Thanks Darrell.  Is that Service Bulletin available anywhere online? 
> I have Information Bulletin #1, but the above information does not 
> show up there.  Wondering what other nuggets of information are 
> contained therein.
>
> I think I may have found the root cause of the problem.  I'm only 
> getting -218 volts of bias on V11 where the schematic indicates -265. 
> I think I have a soft 6BY5 rectifier.  And as I remember it.. the last 
> time I checked that tube it was questionable.  Heck of a time to have 
> my tube checker out on loan.  Caps have already been replaced in the 
> bias supply so short (excuse the pun) of a bad transformer winding, I 
> think replacing the 6BY5 with a fresh tube will do the trick to 
> increase the bias back up to where it should be (and hopefully cure 
> the crystal oscillator problem).  I just ordered one.. we will see!
>
> Thanks all
> Paul  N6EV
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