> Rich, wouldn't it be reasonable to surmise that he's lost the cut-off
bias,
> perhaps because of a contact failure in the much-maligned TL-922 T/R
relay?
> That would certainly explain the plate current on standby, and if the
> normally-open operating bias contacts are OK, also explain why the rig
> appears to be normal in "operate" mode.
That was what I thought too, but the 3-500Z is a zero bias tube, so it would
be unlikely to take 500mA even if the grid was grounded.
I surmise there has been an arc, this has blown the meter shunt and the
meter is now reading the leakage current. If it is a sensitive meter, this
is possible. Hopefully, there are meter protection diodes or the coil won't
last. It might be that the meter protection diode has also failed short
circuit and is acting as a shunt itself limiting the current reading to
500mA. You can soon find out as if the anodes are glowing brightly on
standby the current is real. If they are dark, then the current can't be
500mA.
If the meter is not at full scale, and the current goes up with RF input,
then perhaps there is indeed a grid-cathode short and a particularly active
tube or an ongoing parasitic.
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