How essential is an isolation transformer?

[Yorkie]

There was a thread earlier this year before you joined the forum Nick, (started by someone who is no longer a member), which resulted in a debate about the safety aspects of using isolation transformers.

A few of the posts generated more heat than light, but overall, there was a lot of useful info imparted which you might find  interesting  Nick.

You won't find it difficult to sort the wheat from the chaff:

http://golbornevintageradio.co.uk/forum/...ransformer

I always do as much testing on any equipment with the mains lead unplugged. A great deal of diagnostic testing can be done without the equipment powered up and it's good practice anyway. EG, the continuity of heater supplies, checking transformers for open circuit, checking the continuity of inductors, transformers, switches, checking if resistors are within tolerance. AC only equipment  has an inbuilt 'isolation transformer' in that only the primary is connected across the mains. When checking voltages I always clamp the ground lead to chassis, then I only need one hand to use the positive prod to poke around with, and concentrate on what I'm doing because it's so easy on say small valve-holders (B9A, B7G) to slip and short two pins together.

I do have an isolation transformer and use it when working on AC/DC sets, which isn't very often.

(There have been examples of restorers connecting earthed test gear such as a signal generator or scope to live chassis radios with interesting consequences).