[Amps] Alpha 77Dx -Adding Grounded Grid Filament Choke

[Paul Christensen]

> While you are 'in the area" check for heater voltage at the tube pins with
a
> good RMS voltmeter.
> I have never found a 77DX/SX with the proper heater voltage. I assume the
> transformers were wound for 230 volts. My line voltage here is a stiff 242
> volts.

Mine too - like 245V.  I think a better solution in the initial 77Dx design
(and all amp designs for that matter) would have been to use an independent
filament transformer to allow for the control of the heater as a function of
the user's line voltage.  A rear panel rheostat on the primary together with
current-limited test point jacks for a true RMS voltage sample would have
been ideal.

I suppose the existing primary could still be done in this manner -- only
plate voltage would also change as the heater voltage was adjusted in the
transformer primary since the primary is common to both plate and heater
secondaries.

-Paul, W9AC