[Amps] Query: AC Switching of High voltage

[k7fm]

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