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Old 21st Sep 2019, 9:19 pm   #1
RobertF
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Default Avo valve characteristic meter

I have been offered an Avo valve characretistic meter, which I know very little about. I cannot see any model number showing.

I am attaching photos. Does anyone know this tester?. I don't know if it works as it hasn't been tested. Was it a reliable model in its day?
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Last edited by RobertF; 21st Sep 2019 at 9:31 pm.
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Old 21st Sep 2019, 10:46 pm   #2
fetteler
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Default Re: Avo valve characteristic meter

It looks like a mkII (mk2) to me. All AVO stuff was reliable in its day, these are well made testers but because there is no accounting for what has happened to it during its life it should have a good 'going over' before use. I for one would not hesitate to have it

Cheers,
Steve.

PS, I just thought... if for whatever reason you decide not to take it then I would certainly like it!!!!!
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Old 22nd Sep 2019, 5:33 am   #3
Radio Wrangler
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Default Re: Avo valve characteristic meter

Definitely a VCM Mk II

They're quite good mutual conductance testers, though the meter is not as sensitive as the Mk III onwards models, so their leakage tests are not as sensitive.

Two warnings:

1) it can be easily damaged by inappropriate settings of controls, so there is risk of damage from a previous user, also you need to read-up on correct operation before trying to use it.

2) Some people try to use valve testers to 'burn-in' valves. Don't! they are designed and rated for just quick tests.

I speak as someone who bought one as a teenager, and ruined the meter. I've regretted it ever since.

David
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Old 22nd Sep 2019, 7:44 am   #4
Craig Sawyers
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Default Re: Avo valve characteristic meter

I have one with a pre-damaged meter. But I was given it for nowt, so I can't complain.

The way around a bust meter movement (open circuit) is to buy a (cheap) plastic meter of whatever sensitivity seems reasonable. Cut away the plastic (Dremel) to leave a small amount around the movement. Remove old the movement from the AVO meter, and carefully mount the new movement into the old meter case with hot melt or similar.

You can then use an op-amp circuit to have the same input resistance as the original meter, and the correct gain to mimic the sensitivity.

That way you get a meter that looks correct, and has the original scale.

Craig

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Old 22nd Sep 2019, 10:50 am   #5
David Simpson
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Default Re: Avo valve characteristic meter

MK1's & 2's used a 444uA(approx.) fsd meter, as opposed to the 30uA used in MK3's, 4's & the CT160. If in good order & calibration - a reliable tester. Being pulled up by silly prices that its later siblings attract - the MK2's prices are starting to rise. I personally wouldn't cough up more than a couple of hundred quid, unless I'd tried it out & it was in good nick.
There is heaps of info on AVO's range of VCM's, along with heaps of info on op-amp options for replacement metering - all to be found via "Search".

Regards, David
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