On 4/14/2011 8:40 PM, Kenneth Scharf wrote:
I would test any wire would resistor with a grid dip meter to make sure
it ISN'T self resonant on any ham band, otherwise it will fail again.
OR You can prevent the self resonant problem by putting a .01 uf 1000v
ceramic capacitor in parallel with it.

Hi, Ken

I have to disagree with you about the added capacitor you suggest.

The added resistor is intended to act as a fuse,
on the output side of the HV supply. If it opens (by exploding),
the parallel capacitor will have 3 KV across it, assuming
the short condition is still present downstream, so a 1KV rated
capacitor is inadequate.
Plus, we want all of the voltage spike to be across the resistor,
so it blows up "real good". A capacitor across the resistor
would have the effect of slowing the resistor failure time.

There should be little or no rf current in the resistor,
so no need to test it with a grid dipper.
The resistor is isolated from the 3-500Z by the plate choke,
and bypass capacitors shunt the rf to ground in the HV line.

73,
Ed Knobloch