Valve testers, the best?

[David Simpson]

Just thought I'd add another two pennoth.
Building a DC valve tester lends itself to adding on later a signal testing & monitoring facility. The basic DC (Static)function will allow you to easily monitor Ia/Is as well as calculate gm, and hence the valve's mu.(mu = ra x gm).
However, its pretty easy to add on the facility for dynamic testing. Meaning that Gain "G" can be viewed P - P, or measured RMSwise using a VVM.
Expected G can be obtained from the formula G = Rl/ (ra + Rl) x mu, and compared with the valve's performance. ra & anode load Rl are given in Data Books & sheets.
Heater supply is externally from a PSM 3/2A, Signal source is a Farnell FG2, and i/p & o/p waveformes are monitored on a Hameg HM605. The Marconi TF1041C, built into the LeyMarcAvo, is switchable between AC & DC probe facilities.
For anyone contemplating building a DC valve tester, I'd recommend that Va, Vs and the Cathode connection are only able to be connected to the valve under test via a spring-loaded toggle switch and a hefty relay. ie. no finger pressure - - no voltages & currents - - - just for safety.
Tests, so far, on a Brimar43, a Tronix7C5, and a military 6K6GT - have produced excellent results and bode well for the future.

Regards, David