Remember there's a difference between the maximum grid current you
would normally expect to run, and the maximum level you *could* run
without damaging the tube.
Depending on the speed of the trip circuit, it might make sense to set
the trip level about 50% above the maximum you'd normally expect to run.
That leaves the tube well protected, without causing too many nuisance
trips during tune-up.
The same question could also be asked about a suitable full-scale value
for the grid current meter. I generally make it so the normal reading is
about 2/3 of full scale, and then set the current trip at full scale.
BTW, all this can be done by pulling out the tube and using an external
power supply to force current through that part of the circuit. The idea
is to get all the metering and protection circuits calibrated and
working *before* the first time you light the tube,
In my experience of running this tube on 50Mhz expect to see around 100mA in
practice when the max recommended cathode emission is reached. I would set
the grid trip higher than Ian suggested at around 225mA. The important thing
is not to run more than an amp (average) of cathode current, the tube also
likes 3.5kV when it really comes alive. It is a wonderful tube in my opinion
and beats the pants off the Russian tubes despite claims of the Russian
tubes being similar. I run both a GS35B and a 8877, give me a 8877 every
time.
I have had no problems with golden balls :-)
Conrad G0RUZ
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