[AMPS] MEASURING FILAMENT VOLTAGE

[Peter Chadwick]

Rich said:

>The presence of RF  adds virtually no useful inforation.  

..........but in most cases, it drives the DMM mad.

Holding off the sensing with say 1Kohm resistors and suitable bypass caps and
screened leads might do it, but I've been bitten  a number of times  by RF
getting into the DMM. On one occasion, a class AB1 grounded cathode amplifier
was producing full output power but the screen grid was 600 volts negative
w.r.t. cathode! With no drive, it was +300. These days, I use the old fashioned
Avo 8  moving coil analogue device for measurements when there's a lot of RF
around. Like Rich, I doubt that measuring the filament volts with RF will
provide any useful info. If you see the filament colur change as you drive the
amp, maybe you need to do that.



73

Peter G3RZP



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