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!

There are different types of isolation transformers. The ones many sell in
US with outlets and all, have three prong grounded outlets, and that groung
is tied to one leg of output forming new neutral. These are specific for
reducing noise. No ground isolation.

Greg