Introduction
For some time I’ve been postponing the conclusion of a half-finished project. This is one of the many projects that I have around as many of you, but it was time to complete it as just some minor bits were outstanding.
My interest in measuring valve transconductance was very high since my early days of involvement with hollow state technology. The old valve tester I acquired didn’t measure it, I tried many ways to measuring it with different methods until I settled with using a CCS load and an AC meter as described here.
The problem I found though was that my true RMS AC meter in low scale (i.e. 100mV AC) didn’t like a significant DC voltage drop across the sensing resistor. Not sure why, but either way I wasn’t happy either without decoupling the anode to the sensing part of the circuit when using high voltages.