: Hi Bert
: I am working on a new VTTC project and I have to measure the grid current
: (don't want to go over the ratings of the tube, even I dont know very well
: what is the maximum permited). The tube is a GU5B russian stuff.
: I made a little drawing: what is the correct way to introduce the DC
: A-meter in the circuit to get the right reading? A, B, or C variant?
: Thanx a lot
All three approaches will work. However, I would recommend configurations "A" or "B" since these allow the meter to operates at near ground potential. I would, however, recommend adding a small bypass capacitor across the meter to bypass its coil inductance. Configuration C may subject the meter to high voltage stress, especially if the meter uses metal case. This can represent a shock hazard (of the case is not grounded) and may coil-case flashover if the case is grounded (for safety).
Good luck and best wishes,