Hacker News Reader

Comment by Jeema101 | Hacker News Reader

>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.stackexchange.com/questions/17496/how-is...

It also limits the total current to whatever the transformer can supply before voltage starts to sag.

View on HN

> It's not true to say that it does nothing for safety, though.

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).

> It provides isolation vs ground and prevents the circuit from being completed through your feet and the floor:

Ah I think I see what you're getting at. Are you saying if your feet are at the same potential as the chassis then there's an alternative DC path to ground through your body, which the iso transformer breaks?

That's a good point, needed to think about that one a bit!

EDIT: Hmm, in that circumstance you'd be safe (from grounding DC through your feet) if the chassis was live! If the chassis was connected to AC neutral then your body could offer a path for high voltage DC to complete the circuit back to the chassis, but not if it was connected to AC line (hot). Quite an interesting thought.

Reply on news.ycombinator.com