[Eliot Ness]

I gave up trying to find a PR57 because they were all going for more than I wanted to pay.  I did find a similar BK1655 on eBay a couple of years back that was much more reasonable, so you might want to search for one of those.  In the mean time pairing your isolation xfrmer with a variac is a good solution.

I have an old General Radio Company W5MT3 variac that is built like a tank that I bought at a hamfest several years ago pretty cheap.  I still see them on eBay but they aren't quite as cheap anymore:

http://www.ebay.com/itm/General-Radio-Tr...SwpdpVcQVj