Earlier quoted context omitted.
Just to be pedantic (I think it's ok given the venue...) - All an isolation transformer (which is an external component you have to supply; it's never part of the radio) does is make the mains AC voltage inside the radio "float" in contrast with the voltage coming from the wall outlet (which is of course referenced to the actual ground outside your house). This makes things a little safer because if the chassis becom…
>Isolation transformers do nothing for safety concerning the dangerously high DC voltages which the tubes run on. Yes, you can still receive a fatal shock via one arm to the other even with an isolation transformer. It's not true to say that it does nothing for safety, though. It provides isolation vs ground and prevents the circuit from being completed through your feet and the floor: https://electronics.stackexchan…
I didn't, I said it did nothing for safety concerning DC :) In the prior bullet I explained an iso transformer's contribution to safety regarding AC.
(Feet/floor not involved in the DC side. DC ground is the chassis, regardless of whether that's floating with respect to AC ground or not.)
EDIT: I'll double down on the pedantry 'cos this stuff does matter. There's no isolation transformer in this radio - it's a piece of benchtop equipment the author (wisely) chose to use. As I was getting at in my comment, I can't think of any radio or amplifier that incorporates an isolation transformer: at the time they were designed nobody cared, and nowadays the law requires you to include a separate chassis safety ground (for class 1 devices of course - class 2 being double insulated which is all but impossible on anything you could plug an external audio input into).