Ivan Vegvary wrote:
Purchased used Variac. Good action, very smooth from 0 to 140V AC.
Question: Input and output are both 2 prong, no ground. Should I modify
it to three prong with ground?
BTW, I do also own a functioning isolation transformer.
Should the IXformer be placed between the mains and the Variac? Please
advise as to best procedure. Thanks. Main use of Variac will be to power
up ancient tube equipment.
Thank you!

I would place ISO XFMR after variac. The transformer is not 1:1 and
designed to be 1:1 under full load. Depends on current either way you can
end up say 160 volts no load.

Greg