There are 2 things you need.
1) a variac with amp & volt metering
2) an isolation transformer
If money is no object get one of these.
https://www.ebay.com/itm/Sencore-PR5...AAAOSwjwJgLTmT
That will do almost anything. B&K also made one. I have used the Sencore
since abt 1974 & only replaced the socket on it once. Great for tube
& solid state. In fact indisposable for solid state work.
73 Zeno
LFOD !