Sorry, I gotta ask. What is a "water resistor" exactly??
![Roll Eyes](https://amfone.net/Amforum/Smileys/classic/rolleyes.gif)
Pure water happens to be an insulator. Add salt (etc.) and it becomes a weak conductor...
I'd been eyeing that title for three days now, finally I had to look, and ask!
![Grin](https://amfone.net/Amforum/Smileys/classic/grin.gif)
_-_-bear
But, yeah a variac, ammeter and voltmeter on the B+ is a good way to go - of course, if you have rectifier tubes, you'll perhaps want to make a provision to feed the primary of the B+ xfrmr from the variac, or else temporarily replace the rectifier tubes with solid state diodes...