k7fm wrote:
> Hi Ron:
>
> There are two different timing circuits used on the 76A. I converted one of
> my amps to use 3CX800A7 tubes and simply added capacitance to easily get 3
> minutes.
>
> One problem with the mercury relays is that they can be activated when the
> amp is put on the side. This could be a safety issue for the unwary.
>
> Switching the high ac voltage adds a new dimension to design. And, it does
> not solve all the problems. The original control circuitry prevents drive
> from being applied until 3 minutes. By just switching the high voltage and
> leaving the original control circuitry, the transceiver could be powered up
> after a minute and you would dump 100 watts into the cathode of the tubes
> with no plate voltage - not good.
Unless there's an interlock to prevent tx when ht is missing. Modifying
the 1min timer to 3min strikes me as safer and probably easier - or make
a 3 minute timer and put it in the tx control lead between the rig and amp?
Steve
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