ORIGINAL MESSAGE:
On Wed, 15 Sep 2010 23:45:00 -0400, "David H Craig"
<davidhcraig@verizon.net> wrote:
>Use the diodes in
>parallel, keep the shunt, and you'll be fine. Just be prepared to replace
>the shunt R & (maybe) the shunted diodes in case of major mishap.
REPLY:
You can protect the shunt resistor and meter by placing a separate
resistor in series with the grid current meter with a value such that
the diode will begin to conduct when the voltage across the meter +
series resistor reaches about .6 VDC. If you use a diode with a large
surge rating such as the 6A10 (400 amps) and you have a glitch
resistor which limits current to a value below that, the diode,
resistors and meter should all survive. Only the fuses will blow.
The only problem you might have is if you use abnormally large filter
capacitors which would make the glitch duration too long. Even then,
with any luck only the diode will be damaged and you are out about 40
cents and some time. A typical filter cap for a 3 kV 1500 watt supply
is about 35-50 uF. Some builders have used as much as 200 uF and more
and that is where things become dicey.
Bill, W6WRT
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