[Amps] Don't do this

Ian White GM3SEK gm3sek at ifwtech.co.uk
Mon Dec 20 00:29:11 PST 2010

Carl wrote:
>Ian, do you have any references to those diodes NOT protecting a 
>SB-200/220 meter?  I certainly dont and have seen many failed 1N400x 
>diodes that saved the meter. Redesigining the Heath circuits is not an 
>option to most users.
Granted - for those particular meters in that particular amplifier.

Carl and I are approaching the problem from two different directions. He 
repairs many examples of the same models with the same faults, so he 
builds up a wide database of experience. But my boards sell mostly to 
individual constructors - every amp is different, and the only way I can 
cover that wide range of unknown situations is to aim for the maximum 
possible protection.

The "0.5V full scale" idea can do that. Bill's method using a series 
resistor is the simplest, while mine will work with a wider range of 


73 from Ian GM3SEK

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