[Boatanchors] High Voltage 400 Hz Supply (David C.

[Drew P.]

David C. Hallam wrote:

> I am considering various ways to build a HV 400 Hz supply
> to calibrate AC VTVM's.  Current requirement is obviously low and I
> need variable voltage up to 300VAC,  So what I need is some type of
> an inverter to convert from 60 Hz to 400 Hz and a transformer to step up
> to 300V.  As I see it, the inverter needs to have a voltage variable
> output, or can accept a variable line input from a 120V 60Hz variac, or I
> need a 400 Hz variac to put on the output.
> 
> Since this will have very limited usage, cost is
> important.  Any suggestions on how to do this at low cost?

You might try a sine wave audio generator set to 400 Hz, feed that into a hi-fi amplifier (soiled state of course), then feed that into a step-up transformer. A 60 Hz transformer will do; you might try a combination of filament-type transformers with the low voltage windings in parallel and the high voltage windings in series to get the voltage you want.   A good single-transformer source might be salvage from a vibrator power supply. Another might be a power transformer intended for vacuum tube applications; use the filament winding for the input and take output from the HV winding which would normally be used for B+ supply. It would be well to add a light resistive load to the secondary of the transformer(s).

The volume control would set the output voltage.

Drew