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.
73, Colin K7FM
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