[R-390] Question about VARIAC

[Bill Hawkins]

An AC magnetic device is designed for a specified Volts/frequency ratio,
like 120/60 Hz = 2.

120/400 Hz is 0.3, so the core is lighter, but it will only support 60 *
0.3 = 18 volts at 60 Hz.

If you keep the magnetic core of the variac, you must keep the same
number of turns.

The size of the wire depends on the room available for that many turns.
A variac winding can't be layered.

The power you can draw depends on the material and weight of the core.

You should use the same size wire for rewinding. You can't get more
power with heavier wire.

Rewind the core first, then flatten the top of the turns with a small
hammer, if necessary.

Use a fine file to remove enamel where the brush will contact the wire.
Polish the exposed wire with 600 grit and crocus cloth to reduce brush
wear.

Your winding should be tight so the wire doesn't move as the brush
moves. Maybe you'll need transformer varnish to hold it in place.

If there's no fuse in the circuit, the brush is most vulnerable.

The rest is best learned by experience.

Bill Hawkins