Just dug this out.

Tried to test a 45. Basically it doesn't work.

It powers up fine. Heater voltage set to 2.5V and looking at the filament that looks about right in terms of glow for a 45. Set 4V and it's too bright. I therefore believe it is supplying about the right heater voltage.

Anode is set to 100. Select anode set to normal. Set mA/V switch is set to mA/V marking.

With these settings it should be possible to set the meter to read zero. However, that's impossible and the lowest value I can back it off to is 4.8 mA/V. But then it slowly rises see 2nd pic.

The Philco 45 is working and known to be good. The switch settings for a 45 are correct according to the AVO Data Manual.

Conclusion is it is bust. I have known that for a long time.

Anyone on the forum know how to fix these meters?

Mod fix the title to AVO?

Cheers.