Hello again. I'm still working on my tube testing project. I have been
trying to determine the transconductance of the 6EJ7 tubes I have. Here
is
my setup: Plate and screen grid at 240 vdc. Heater at 6.3 vdc. Grid 3
tied to cathode. Control grid at -3 vdc tied to cathode through 10 k
resistor. Plate current is reading normal and when I vary the grid
voltage
and devide the change in plate current by the change in control grid
voltage
and multiply by 10 to the 6, I get the expected transconductance. I have
done this using the 240 vdc plate curve and the 200 vdc plate curve. When
I
adjust the control grid voltage from -3 volts towards -2.5 volts the plate
current starts running away and the control grid can't be adjusted any
further. I have to turn the plate supply off to regain control. Using
200
vdc as the plate voltage and approximately -2.75 volts on the control grid
I
measure 15 ma and riseing. Is this normal or is this indicative of a
problem?
Thanks,
D. E.
