Need Help - Hum Noise from Audio Research VS55

I have owned a VS55 for a while. The unit was fine when I used it in US. I like the VS55 sound so much and decided to bring it with me to Singapore. But when I hooked up the VS55 (via 220 v to 110 v transformer) to my Proac speakers, I heard a little hum noise out from the speakers. I do not think that the transformer is the issue as my CJ MV-55 works fine without the hum noise. Any suggestion from VS55 audiogon owner on what I shall do. Shall I change or roll the tubes to get rid of this hum noise sound?
sometimes when you plug in gears into voltage regulators, it can cause humming.
personally i never like to use auto transformers or anything that steps up or step down esp power amps as they can be detrimental to their sound quality.
it would be best if you can convert the vs55 from 110v to 230v.
I did have CJs before like the Premier 140 and had no problems with using voltage regulators. But some gears might be more sensitive though.
good luck
Thanks for the advice. I will contact a local dealer here to convert the voltage.