04-03-2014, 06:26 PM
(This post was last modified: 04-03-2014, 06:28 PM by Radio Fixer.)
As to AVO valve testers they are not that bad David.
I bought a Mk 1 that was spares really and a Mk2 that was restorable a dozen years ago. Both in the end were restored to good working instruments and still are. I did take the pots apart and clean and adjust them, not one was duff.
There only weakness really is the meters and some of that is due to operators overloading them. Yes! there is a cut out mechanism but it is electro-mechanical and on both of mine was well out of adjustment. I have read of restorations where no mention is made of checking and adjusting this. It may not catch every overload but is better than nothing. The best, and both of mine have this, is an OP-AMP circuit that even when over driven is arranged to not supply enough current to damage the meter. One of mine has the original AVO meter, the wrong one and about 30 micro-amps FSD, so really benefits from having it as well as making the AVO think it has the right meter. The other has a 100 micro-amp Maplin meter and again the OP AMP cheats the AVO.
Gary
I bought a Mk 1 that was spares really and a Mk2 that was restorable a dozen years ago. Both in the end were restored to good working instruments and still are. I did take the pots apart and clean and adjust them, not one was duff.
There only weakness really is the meters and some of that is due to operators overloading them. Yes! there is a cut out mechanism but it is electro-mechanical and on both of mine was well out of adjustment. I have read of restorations where no mention is made of checking and adjusting this. It may not catch every overload but is better than nothing. The best, and both of mine have this, is an OP-AMP circuit that even when over driven is arranged to not supply enough current to damage the meter. One of mine has the original AVO meter, the wrong one and about 30 micro-amps FSD, so really benefits from having it as well as making the AVO think it has the right meter. The other has a 100 micro-amp Maplin meter and again the OP AMP cheats the AVO.
Gary
