ASR-33 conversion to 220V

Tony Duell ard at
Thu Dec 7 18:32:58 CST 2006

> As an aside, if I've got 110v equipment and 240v mains, would a yellow 
> transformer be suitable for running it?  I'd assume that most kit will 
> be happy enough with a centre-tapped supply but I don't know if I want 
> to risk it...

AFAIK no equipment, either US or European can assume that one side of the 
mains is grounds (and safe to touch). Therefore a centre-tapped (to 
ground) supply should be fine. One of my Tektronix instruemnts shows 
different wiring for centre-tapped-to-ground and one-side-grounded mains 
(I think only for 230V mains), but this is to reduce noise pickup, not 
safety, and AFAIK the instrument works if you get this wrong (it just has 
a little (and I mean little) more noise on the trace).

I have a cable here with a 110V BS4343 (yellow) plug on one end and a US 
mains socket on the other. I use it for running US mains 
chargers/adapters off a power tool transformer. OK, I only use it for 
testing (to measure the output voltage/characteristics of the US adapter 
so I can make a UK mains equivalent, but I've never had any problems 
running said US adapters off the power tool transformer.

[For those who wonder what on earth I am talking about, portable 
industrial power tools -- electric drills, for example -- in the UK are 
110V devices. They're run off a step-down isolating transformer, the 
secondary of which is centre-tapped with the tap connected to ground. The 
idea is that if the insulation fails, or you cut through the cable, or, 
then the maximu voltage you'll get if you touch one bit of metal is 55V 
(one half of the transformer output, returning to ground through you). 
This voltage is unlikely to prove fatal.]


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