> > A rheostat in the HV transformer primary is bananas.
>
>
> Why? Too much loss?
>
No, because it will wreck the regulation. Most amp PSUs use capacative
filters after the rectifier to provide the HV supply. A feature of
capacative filtering is the high ratio of the peak current supplied from the
rectifier into the filter capacitor with respect to the mean current
supplied to the amplifier. The proper thing to use on the HV primary is a
variac.
Rheostat = device whose resistance to electric current depends on the
position of some mechanical element or control in the device.
Variac = transformer whose transformation ratio depends on the position of
some mechanical element or control in the device.
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