Hi, thank you for your responses:
> From: Carl Clawson <carlclawson@verizon.net>
> Hi Marius,
> Your scenario can happen. I recently saw B- arcing to the chassis through
> the insulation on low voltage wiring in an LK500-ZB amplifier. It had
> suffered an HV arc during which the grid meter shunt resistor blew open.
> This resistor was the only thing holding B- near ground, so it could now
> float downwards to a dangerous value. An unwary person trying to probe the
> low voltage end of things in this situation could get a nasty surprise.
>
> This is why one of the recent topics on the reflector has been the use of a
> stout diode from B- to ground, so that in case of a fault B- can't go far
> below ground.
>
> 73, Carl WS7L
OK Carl. Thanks for confirming my analysis. I will definately take
this into consideration in my current / next amp designs.
================================
> From: "Bill, W6WRT" <dezrat1242@yahoo.com>
> REPLY:
> You should not be using a chassis to B- resistor. Use a pair of heavy
> duty diodes instead, reverse connected. When the B+ to chassis arc
> occurs they will place what is essentially a dead short from B+ to B-
> and the fuses or breaker will blow.
>
> Bill, W6WRT
OK Bill, will look into using clamping diodes. Having the meter in
series would case an open in case the meter fails so the meter should
be in parallell with the clamping diodes. I guess there needs to be a
small value drop resistor in paralell with the clamping devices that
have a RI drop that is lower than the voltage where the clamping
device starts to conduct (at max normal tube current). I think I read
something about that in the doc for one of the triode control boards
on the market.
LB3HC
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