Answers obtained from other forums (fora?) in case anyone else wants the info in the future:
- A variac (which is the obvioius answer that I should have thought of)
- An auto transformer made up from a standard mains transformer, ignoring the secondary (one that has 240 and 220 volt taps) - at one’s own risk of course).
- An auto transformer made up of the primary and secondaries of a transformer (there’s a YouTube video on this one, I intend to review and consider if it is crazy or not!).
Interesting that many many folks simply stated “it’s fine” or “UK mains is now rated at 230 volt” (have they never measured their mains?)
…but a few others agreed they have had problems with kit intended for EU voltage (220 volts) running on high 240 volt and failing.
The history is that the EU commission (or whomever makes these decisions) decided that we should harmonise with mainland Europe, so our 240 volts and their 220 volts became 230 volts everywhere.
only they simply widened the tolerances permissible, so no one had to change their power grid.
So now anything really voltage sensitive is more likely to fail in the UK if not made with lots of leeway (which tends to be the case on cheaper gear).
Hey ho…