You can purchase a transformer here https://airlinktransformers.com/category/japan-uk-voltage-converters and it will work absolutely fine. The frequency is irrelevant for an amplifier.
If it doesn't ever happen when there are no lights on in the room it could be related to that. I had a TV that switched channels occasionally whenever a CFL light was switched on.
Even budget amps these days have flat responses and inaudible levels of distortion if used under the maximum power. The McIntosh isn't going to sound better.
The old A1 was class AB, but forward biased to provide around 8 watts in pure class A. It also had a design defect that meant that the volume pot would go noisy because it had DC on it. The B1 was a better effort all round, and more powerful as well.
Class A amplifiers are not really any...