Avo Valve Tester

[pwdrive]

Sounds like oscillation, some valves are capable of oscillating well up in the VHF region, grid stopper/ferrite beads can sometimes offer a solution.

Lawrence.

[Sparks]

I thought as much. It is a known problem with the Mk 1, as it mentions it in the manual. Just keeping one hand on the control whilst testing, seems to be as good a solution as any! Most of my valves are older types anyway.
Bob

[Mike Watterson]

I have ferrite beads on all the wires, per every two sockets, and wiring in a loop.
Later AVOs do this too.