With a Variac on the input, this is a handy for working on line
operated devices that might have a line-to-chassis defect.

Do you actually use a setup like that? I'd think that for any sort
of current, the filament windings would be melting down even though
they are made of fat wire. For example, at 300 VA of output, you're
looking at ~100 A in the filament winding.




Connecting the HV windings together would probably work a lot better.
Would want to knock out the magnetic shunts too, that can be tricky but
I've done it on several without damaging the windings.