COLIN WONFOR: Step-down transformers with unchanged mains frequency

Colin Wonfor

Hi Colin, Pls can you help me? Can I safely run a USA spec amp designed for 110v 60Hz in the UK on 240v 50Hz, with a step down transformer (but it will still be 50Hz). So many conflicting views across the web. I think a lot of people believe it can work ok the other way round, but not like I am suggesting. I also know that the voltage convertors don't change the frequency. Please can you offer me the definitive answer? Big thanks! Julian.

Two problems come to mind. The transformer will have less turns on it than it would for 50Hz which means that the inductance values will be lower. Next, the smoothing capacitors are chosen for 60Hz thus smaller just bit and you may get hum.

Now both of these problems can cause the transformer to run too hot. The best solution is to have new transformer made. Okay, not cheap. Next I tried this and it works 90% of the time OK, with US guitar amps and some odd power supplies. Get at 230VA (new standard) to 100VAC isolated transformer; fuse it well. You must use a isolated transformer because the breakdown voltage for UK is over 2500V and the US in some states is only 1500V – so play safe.

Running at lower voltage will reduce the flux density and the transformer should stay cooler – but keep a eye on it. Some problems may also happen inside i.e. the regulated power supplies may now be out of tolerance due to the secondary voltage being lower so check this also. DO SEE A SKILLED TECHNICIAN to do this before you spend money. He may have a variable transformers or Variac to test before you pay money out.

Good luck

Thank you for the question.

Colin