> Several months ago the amp when 'bang' while running on 40 meters.
> (Actually, it went 'FWOOOOP!!' since I did have a 20 ohm surge resistor in
> the B+; controlled 'bang'.) The culprit was traced to be a Millen HV
> connector which arced thru at 4kv. (I know the tendancy for these
> connectors to absorb moisture has been discussed here.) The surge resistor
> was blown apart as expected. Replace both pieces With the amp off using
> external low voltage pwr supply, the grid trip circuit was adjusted for 75
> mils and the grid current meter was calibrated.
I use an over-sized hole with the Millen connectors and mount them on
Teflon or plexiglass sheet bolted to the chassis. This will end your arcing
problem with these connectors. The red and black ones are made of better
material than the yellow ones. (Millen) Never use the yellow ones above
2000 volts or so.
Either your HV glitch resistor is too small, or your breaker/fuses in the
primary of your HV supply are too large. Shorting the HV should cause
the breakers/fuses to shut down the HV, and the glitch resistor should be
robust enough to drain off the stored energy in the filter caps without
destroying itself.
>fired up and keyed, the amp draws no plate current, and at the
> slightest hint of RF the grid current climbs and quickly trips out. Our
> first thought was the HV had gone away, but it is still there. I didn't
> see it, but was told there is a slight twitch or rise in the plate current
> as the grid shoots up.
Is there any resting plate current when you key up before you apply drive?
Do a continuity check from the cathode of the tube all the way to the B-
point in the power supply and let us know what you find.
GL Steve,
Phil, K5PC
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