Isolation transformer

[ppppenguin]

I usually use an isolating TX with live chassis sets, simply because I routinely want to use my oscilloscope with problems. I'm well aware that it negates RCD protection. If I touched the HT on such a set without the TX, I'd get a belt but the RCD would trip to ensure it was a very brief one. With the TX it would be like touching the HT on a set with a double wound mains transformer. I'd get the belt and nothing would trip.

Actually it's more nuanced than that. If I'm using the isolating TX and no earthed kit is connected I can touch any part of the set, including HT and get only a minor belt due to my own capacitance to earth.