[sdiy] isolating variac unit

[anthony]

Hello, All

I am updating a handy Variac box I made, putting a Powerstat in a pretty 
good sized enclosure, with fuse and back and three-prong grounded jack and 
toggle switch on front.

The first update is to add an isoltation transormer. I did not know at the 
time that Variacs do not isolate the circuit they are powering from the 
powerline. There's no room inside for a 1:1, so I'm using 2 transformers in 
a step-down-step-up configuration. My question is, should I just use non 
center-tapped transformers, or would it be better to use center-tapped 
transformers and ground the tap to the chassis along with the grounds from 
the plug and outlet.

Second update is an AC voltage meter. Does it really matter for Variac-type 
uses to have a true RMS meter or could I just rectify and filter it and show 
that voltage.

Thirdly, I want a neon bulb for an "ON" indicator, but those always end up 
flickering or not working. Why does this happen and how can I prevent it?