(06-06-2024, 03:55 PM)PerdioPal Wrote: A detailed picture (or two showing both states of polarity) of the auxiliary meter would interest me.I have just made a brief video for you showing a variable negative, then positive, voltage being fed into the meter.
See here: https://youtube.com/shorts/9L9c-ygj4cY
10 volt DC supply fed through reversing switch 100K potentiometer driving meter input.
I just happened to have a DPDT switch wired as a reversing switch from something I was testing recently.
The video shows the onset of polarity indication movement as the input voltage is increased, this seems to be independent of meter range, i.e. it always start to move significantly at around 10% of main needle movement.
The service manual I liked to previously has a description of the circuit used.
Test setup:
Best regards, David.
p.s.
I tried comparing resistance measurement with the HP3478A and I'm quite happy it is as accurate as the needle interpretation can give.
I must make a meter test box for checking calibrations, I've been given a box full of assorted high-stab resistors of various values.
The meter is averaging only on AC unfortunately but has a bandwidth up to around 30 kHz.
