Robert Kirkland wrote:
>The Alpha 76 indicates plate current by converting an 0-1 ma. old 1000 ohm
>iron vane meter to a volt meter and measuring the voltage drop through a
>series resistor. The volt meter circuit has an adjustable pot. You would
>think it could be calibrated, power off, with an ohm meter and work ok,
>1ma=1000 ohms per volt. It didn't work, does anyone know how this circuit is
>calibrated or how ETO set it up. I can make it work but would like to
>restore it properly, tnx.
I doubt if it's practical to do the calibration using an ohm-meter
alone. However, it certainly can be done by using an external
low-voltage supply to push an accurately known current through the
series resistor from an external supply (with the rest of the amplifier
totally dead and disconnected).
The method is explained in the user manual for my Triode Board
(downloadable from the url below). Although the Alpha amps tend to use a
different arrangement for biasing and metering, the same method can be
applied.
--
73 from Ian GM3SEK
http://www.ifwtech.co.uk/g3sek
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