[Amps] Query: AC Switching of High voltage

[Steve Thompson]

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