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Vintage Test Gear and Workshop Equipment For discussions about vintage test gear and workshop equipment such as coil winders. |
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Thread Tools |
23rd Nov 2021, 6:25 pm | #21 |
Nonode
Join Date: Mar 2008
Location: Aberdeen, UK.
Posts: 2,838
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Re: How to use this valve tester?
Haan Anwash,
AVO & many other makers use either valve or semi-conductor rectifiers. The AVO MK3 uses D77 small double diode valves, for example. But their main use is to just half-wave rectify sinewaves for 10mS pulses of voltages on the screen(if used) or grid. The AVO's have full P-P sinewaves on a valve's anode(& hence the meter, so take care). The meter balancing(backing-off) network also requires a half-wave pulse. No capacitive input filters with a big choke & large electrolytic capacitors. I'll attach a "loosely pictorial" circuit representation of an AVO CT160's( a MK3 in a military clamshell case, more or less) operation. AVO's full circuit diagrams are similar to Calcutta's or Mumbai's Railway Station network, so difficult to follow. Regards, David |
23rd Nov 2021, 8:30 pm | #22 |
Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
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Re: How to use this valve tester?
There was a modification for the Avo VCM MKIII to convert from valve rectifiers to silicon rectifiers, the anode supply is full sinusoidal AC, the screen grid supply is raw unfiltered half wave, and the control grid supply is raw unfiltered full wave.
I did a drawing some moons ago of a simplified part of the Avo VCM MKIII schematic which shows the control grid waveforms (see attached drawing) showing half wave for calibrating the voltage supply to the control grid circuit and full wave for normal operation...'scooze the scrawl. Lawrence. |
24th Nov 2021, 12:07 pm | #23 | |
Nonode
Join Date: Mar 2008
Location: Aberdeen, UK.
Posts: 2,838
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Re: How to use this valve tester?
Quote:
Regards, David |
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