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Old 26th Sep 2021, 8:27 pm   #81
Stevie342000
Hexode
 
Join Date: Jan 2006
Location: Greater Manchester, UK.
Posts: 373
Default AVT - Two Panel Avo Valve Tester

I finally got around to measuring that resistor yesterday Ed

The resistor is the approx 40R according to circuit diagram it measures 42.2 to 42.6R on DVM. I am still cursing myself for breaking the paxolin board.

What are my next steps?

Do I rewind it ?
Do I try to glue the paxolin tag strip?
If so with what?

Open to idea. I want this working pretty soon. I know the best tester is the circuit it sits in but at least I have a toy that I can use to test there are not shorts or anything seriously wrong before I plug the valve into the ultimate valve tester the circuit is to be used in.

Last edited by Station X; 26th Sep 2021 at 8:38 pm. Reason: Threads merged.
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Old 26th Sep 2021, 8:32 pm   #82
Ed_Dinning
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Join Date: Jan 2004
Location: Newcastle upon Tyne, Tyne & Wear, UK.
Posts: 8,173
Default Re: AVT - Two Panel Avo Valve Tester

Hi Steve, it sounds not too far off. you could certainly try series or parallel combinations of modern metal film resistors to get it reading correctly.
Rewinding is the other option if you can get the correct size of resistance wire

Ed
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Old 26th Sep 2021, 9:26 pm   #83
Stevie342000
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Join Date: Jan 2006
Location: Greater Manchester, UK.
Posts: 373
Default Re: AVT - AVO Two Panel Valve Tester?

Thanks for such a prompt reply Ed. I will check my supply of 1% metal film resistors which I assume would be a suitable replacement.

I think I have 0.5, 1 and 2 watt choices, which is the best power rating?

I know that the meter circuit only takes a milliamp or so but more concerned about the voltage on the meter or through the 40R resistor?

I broke the paxolin not far short of the end of the turns right by the end where it is still attached to one of the legs of the mains transformer. I may well rewind it and reattach it but I am loath to play around with it more than I need to in the repairs that I need to do.

I have still yet to replace any capacitors or check any other resistors in the circuit. The one I recall in the main panel looks like a fuse white body and I am led to believe that these are likely to be still be accurate.

As for replacing the capacitors not sure as there is only DC in the meter circuit I assume? Would the capacitors along with a few resistors (if I recall correctly) be likely to be used to stop DC getting back into the main panel and causing any damage to the other parts of the circuit. Those are the ones I am going to replace.

My research has led me to the conclusion that contrary to opinion there is no need to replace much in these and it is self calibrating once I replace that approx. 40R resistor and that this a very versatile piece of test equipment all told.

Aside from the High slope later valves such as ECC88 or 6AS7G/6080 which are likely to cause it to oscillate. It is certainly much easier to repair than a MK1 to VCM163 or CT160. There is a contradiction in the Avo manual as well if I recall the 1958 edition says you can test a 6AS7G but not a 6080, the 1974 edition does not have the same data as some of it has dropped out (pretty sure it makes not mention of the AVT), the 1965 edition says neither 6AS7 or 6080 and the 1968 version is the last mention I have of the quick way to use and set up the AVT. If my memory serves but then I have slept since I looked at it yesterday.

Thanks to all that gave me help and it has taken me some time to get this far but then it always does take time to get the right information and to draw suitable conclusions.

I have just seen the Dave Hallet video on YouTube and its follow up he reckons in today's money the AVT would cost about £800 plus....ouch that was a lot in the late 30s.

I did think when I watched the 1st part that the neon had not lit so that was where his issue was. In the 2nd video does not really mention what he replaced it with.

It would be this http://www.r-type.org/exhib/aaq0321.htm
which you can buy from the website that has Mullard plastered all over the top of it I can not locate it right now. Found it here: https://mullard.org/collections/vcm-...test-equipment

Last edited by Stevie342000; 26th Sep 2021 at 9:31 pm. Reason: Missing Info
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