[TMC] GPR-90/GSB-1 CW note

[Duncan Brown]

Chris,

As Roy mentioned, the distortion may be caused by 60 Hz hum.

I had a problem with hum on our TMC SBT-1KV transmitter that came from 
the SBE-6 exciter. TMC used the tube sockets for filament ground return 
and poor contact between the tube socket & chassis caused the hum (from 
multiple tube sockets).  I ended up adding an extra wire for the ground 
return for each tube in the low-level stages.

I don't remember if the GPR-90 is wired this way, but something else to 
check.

Good Luck & Have Fun,

Duncan
K2OEQ

On 04-Mar-16 20:24, Chris Kepus wrote:
> I've  been enjoying my GPR-90 / GSB-1 combo during one of the regular
> "exercise" periods the combo gets about every 3 to four months.
>
>   
>
> However, this time,  I detect some minor distortion in the CW note of both
> strong and not so strong CW signals and on AM signals.  This "distortion" is
> noted whether I'm listening to the GPR-90 audio or the GSB-1 audio.  In
> looking at the signal path prior to the IF takeoff for the GSB-1, I  am
> trying to figure how to isolate the cause of the distortion.  I do plan to
> change out each of the tubes, one at a time,  just to eliminate them as a
> possible cause.  Both units play very well otherwise, I am a bit baffled by
> this problem.
>
>   
>
> I am looking for ideas as to potential component culprits;  any and all
> comments, questions, are welcomed.
>
>   
>
> Available at the test bench are RF and AF signal generators, TEK scope,
> VTVM's, multimeters, etc.
>
>   
>
> Thanks es 73,
>
> Chris
>
> W7JPG
>
>   
>
>   
>
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