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Old 31st May 2019, 11:00 am   #10
David Simpson
Octode
 
Join Date: Mar 2008
Location: Aberdeen, UK.
Posts: 1,960
Default Re: AVO VCM MkIII repair

Mike, follow Martin's advice & study the Manual. AVO VCM's & just about all valve testers, use transformer secondary derived AC voltage's peak waveforms for testing Ia & mA/V. Yes, switch selections indicate RMS voltages, but they are NOT DC.
I've attached a very simplified diagram of how an AVO CT160 (A MK3 in a clam-shell case, more or less) works.
Have a good shufti through "Search" - masses of info on MK3's & all the other AVO testers, & much banging-on by some of us VCM enthusiasts over many years.
Just to help you understand the AC waveforms & 20mS half-wave pulses - use an oscilloscope on the anode, screen & grid. Also remember - full AC peak to peak voltage is on the meter terminals & the relay contacts, so please take care.

Regards, David
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