[David Simpson]

Its great to hear that more & more Forum folk are taking up homebrew valve tester projects. From my own experience its a slow, but invigorating process. Involving quite a measure of "Suck it & see" design considerations.
Right enough, the 9 pin/9 way switching design involves a lot of thought & temp. circuitry pencil drawings. I've a thread running in "Test Eq." about a Roberts Valve Tester", and another associated thread in "Components" about Wafer Switches - particularly RS Components' MAKA SWITCH rotary switch construction kit. I've a spare AVO VCM Thumbwheel Switch assembly, but its too an expensive spare for my MK3 if anything ever went wrong. I had considered stripping out a lovely old Muirhead Decade Resistance Box, of Lab quality, for the 10 way switches, but thought that I'd probably be blackballed from the Forum if I did. So I'm plumbing for the MAKA switches, 9 newly bought 2P on/off/on Toggle switches, and some 2nd hand Yaxely type paxolin rotary switches recovered from the Roberts'.
In fact, just this morning, I've decided to use a spare AVO8, fitted into the cabinet, to measure most of the valve's electrode's voltages & currents. Instead of fannying about with several different meters & heaps of shunts & multipliers. I reckon myself & many other forum valve testing enthusiasts can build a self-designed versatile DC valve tester for under 200 quid tops. Some folk might want an easy mA/V display Dial/Pot relating to an AVO-like bridge network, but me thinks that a simpler method of introducing delta Vg to the grid is achievable, whilst observing Ia.

Regards, David