[R-390] Distortion troubleshooting

[Roy Morgan]

At 02:07 PM 3/11/02 -0500, Bill Cotter wrote:
>One theory that sounds appealing to explore is the parasitics possibility, 
>is sounds so mysterious and ghostly. ... the RF deck would have to be 
>removed,

Not necessarily.

Get a scope onto the test points along the RF chain.

Listen to the signals inside the radio with another radio.  (Put the 
antenna wire near or around the tube of the stage you want to listen to.)

Hook a little wire onto the grid pin of a tube and connect to that.

Feed modulated signals from your signal generator into the test points with 
preceding tubes pulled out.

Watch the audio output on a scope.

Roy




>  The second is an internmod problem in the mixers. Chasing both of these 
> may cost long hours of bench-instrument time, and since
>
>That's the one you suggested of examining all the resistors and capacitors 
>for out of spec condition. Along with examining all solder joints, 
>connections and, the grounds of all shields, sockets and posts.
>
>To all that replied - Thanks,
>
>bill n4alg
>
>
>> From what you describe, it sounds like the set is operating normally when
>>there is little or no AVC voltage, and it sounds like the set may not be
>>operating normally with a strong signal, but the signal is getting through
>>anyway.  In between you hear distortion, where some stage is affected by 
>>AVC but can not operate normally.
>>
>>Sounds like a "fun" problem to troubleshoot.  You'll feel great when you
>>find it!  :-)
>>
>>73 de Bill, AB6MT
>>billsmith@ispwest.com
>
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- Roy Morgan, K1LKY since 1959 - Keep 'em Glowing!
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