On Fri, 02 Nov 2018 21:43:18 -0700, 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?

I certainly would.


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!

The isolation transformer should always power the *device under test* to
remove the Earth reference from it.




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