On 26/02/2014 17:32, Dave Plowman (News) wrote:
Bought a bit of audio gear from the US at a decent price even allowing for
carriage. Guessed it might be 110v - but it is actually marked 120v 60Hz.

Looking inside, it has an analogue power supply - I was rather expecting
an SMPS.

That could spell trouble keep a *very* careful eye on it for signs of
overheating. US made kit for their domestic market tends to cut it
extremely fine on the saturation of the transformer and the shift in
frequency from 60Hz down to 50Hz will allow a higher current to flow.
One of my first jobs was to determine why a particular US made colour
monitor died prematurely and sometimes even caught fire in the UK.

The transformer primary has two winding wired in parallel which seem to be
coil 1 black start brown end, coil 2 red start orange end.

Red and black are paralleled as are brown and orange. Red/Black goes to
neutral, brown/orange to the off/on switch.

So it looks like I may be lucky and simply altering them to series will do
it for 240v. Link brown and red and 240 goes between black to orange?
Does it matter if one winding has the connections reversed when they are
in series?

Yes. Get it wrong and the two windings magnetic fields will cancel each
other out resulting in an almost non inductive load. Check with an LCR
meter to establish which way round produces a 2L load as opposed to an
almost pure resistive one with a tiny inductance.

And really keep an eye on it for overheating. The change from 60 to 50Hz
can saturate the transformer cores on some US kit! Their electronic
designers often can't imagine anywhere outside the USA!

Japanese stuff is always OK anywhere as they have half 50Hz UK and half
USA 60Hz frequency depending on which part of the country you live in!

--
Regards,
Martin Brown