[AMPS] Full QSK for the SB-200

[Richard Carroll]

Tom Branch wrote:

> Greetings,

>  The presence of RF grounds the filament winding and
> turns the tube on.  The absence of RF applies +125 volts to switch them
> off.
>
> I'm thinking about combining this circuit with the fast T/R portion of the
> Rich Measures' circuit to give the SB-200 full QSK.  Additionally the grid
> bias circuit could be permanently grounded instead of running it through
> the T/R relay.
>
> Seems reasonable, although I'm not sure what impact it would have long-term
> on the 572Bs. I wonder if they are truly "instant on" to support this
> concept.
>
> Any thoughts?

Story from Eimac VIA W6SAI in Ham Radio magazine went that a ham had tube
failure in his SB220 , not once or twice, but 3 times, within the tubes'
original warranty. After the third replacement, Eimac called him to see if they
could find out why he was experiencing so much shorter tube life than anyone
else. Turned out he had his filament line tied to the PTT line on his rig VIA a
relay. Each time he keyed up the mike he also turned on the instant-on
filaments, and when he let up they went off.. But they just won't hack that
kind of cycling on and off and the filaments would soon open. Based on that
case it doesn't seem like a good idea.

Dick W0EX


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