[Amps] Grid Protection Circuit Ideas

[Allen Jones]

I have a Heatkit SB-230 amp and would like to add
protection for the grid.  I'm not an engineer but it
looks like a simple transistor switch with a latching
relay will not suffice as it would be difficult to
develop the 0.6 to 0.7 VDC needed with the low amount
of grid current that normally flows in the metering
circuit.  Eimac specs the tube at 30ma max.

I was told to use a circuit similar to the one in the
Ameritron AL-800 or 1200 which uses an op amp.  The
manuals are available on the Ameritron site but do not
contain schematics.  Any suggestions or assistance
will be much appreciated.

Allen, W9DZ


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