Avo mk2 valve Tester

[pwdrive]

Gary wrote "The Mullard High Speed Tester to me has many disadvantages. The boxes of cards takes up a lot of space and then the very one you need is often missing from sets containing 100s. Also, I would prefer to make my own judgement, from meter readings, on a valve being good or bad and not discard on a go / no go light. Speed of testing for a hobbyist isnt an issue"

Hi Gary, yes the high speed valve tester was primarily a service dept machine and as such was designed for that as it took some abusing, the main role of its use in the service depts I worked in was for quick testing of television valves,
back in those days it was mainly PCL82's, PCL85's PY33's PCL84's etc etc.

Lawrence.

[AlanBeckett]

Why can't you turn the original scale over, paint it white and start from there.
I've done it before.

Alan

[Yorkie]

I don't think that model of meter actually has a scale at all Alan, which is why they well them separately. The meter just has a shield over the movement. The issue for Avo valve tester meters is getting one with an acceptable sensitivity, and the right physical size and scale length. The Anders CV-20X model is 100mm x 83mm – close to the CT160 Avo, which I think is 115 x 83mm.

The original Avo movements were 30uA and very fragile, and prone to failure. Gary’s solution was, I believe, to use a 100uA meter - far more commonplace and more robust, and to drive it with an op amp. The authors of the RB Feb/Mar 2012 article favoured the use of the Simpson 25uA taut-band meter, type No 03951, (with a shunt to get it to read FSD as would a 30uA meter), but state that they’re expensive ($217 AUS), but that they’d picked up eight NOS ones in the States for $17US each.

In one instance they’d transplanted the movement into the AVO meter case, which must be a very ticklish operation, rather than replace the AVO with the Simpson which involves a bit of filing.

It’s of no direct interest to me as such, as I don’t own an AVO valve tester nor am ever likely to, but it’s an interesting topic in that it’s a good example of amateur restorers finding ‘work-arounds’ to overcome the shortcomings and keep the testers in working order. Simpson have quite a list of UK based distributors of their meters:

http://simpsonelectric.com/index.asp?p=F...istributor

An interesting US company with quite an illustrious history, and still going strong today, despite the competition from China etc. Simpson Electric’s prominence in the panel and test instrument industry dates back to 1927, when the founder, Ray Simpson, built the indicating mechanism for the earth inductor compass that Charles Lindbergh relied upon when he flew “The Spirit of St. Louis” on the first solo flight across the Atlantic Ocean. For thirty-three hours, Lindbergh’s life and success of his historic flight depended largely on this navigational instrument, while the world awaited his arrival in Paris. The 1960s saw Simpson Electric as part of the American NASA space programme by developing a special two-movement, cross-pointer instrument for the Apollo missions.

[Radio Fixer]

In mk 1 and 2 testers, the meters were nominally 440 micro A. later models use the 30 micro A.

In the two I made useful again one did have an incorrect but good 30 micro A meter in it though.

Gary

[kevin.Hoyland]

Thanks for the link to the meter Nick.
Regards Kev.