I imagine this has already been mentioned, but with 3-500Z amps, a negative
pinning grid current is often an indication of a grid-plate short, or a
gassy tube. If there is a conduction path between the anode and the grid,
then plate current will flow to ground, via the grounded grid. The current
then flows from ground up through the grid current resistor (typically 10
ohm or so) into the B- lead of the power supply. This causes the grid
current meter to peg backwards. Fortunately, a protection diode usually
protects the meter from damage.
73,
Jim W8ZR
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|