VACUTRACE Vacuum Tube Curve Tracer
13
In gm (transconductance) mode, a 625Hz modulation is added to the grid output.
The dynamic peak-to-peak grid voltage is used as the reference for the LED analog-
to-digital converter and the resulting cathode current modulation (just the ac
component) is used as the input. This creates an analog divider circuit to calculate
∂
Ik/
∂
Vg, which is transconductance gain. Similarly, in gp mode, the plate voltage is
modulated and dynamic cathode current measured to determine output conductance.
