I was interested in building my own safer version of using a variac to brown out the power supply. Rather than having a rotating part that your drummer could kick and send your amp up in flames, I wanted to mount a simple power transformer in a box with taps for 110, 90V, etc... I found this Hammond that has the appropriate taps: http://www.mouser.com/Search/ProductDetail.aspx?qs=3GbUB62Nf7cdaEx96r5amQ== My question is, what VA rating should I be looking for? I found a general approximation of using 1.67xpower. Assuming they mean peak power in that equation, and for a 100 watt rms amp, 100x2^(1/2)x1.67=236... So the above transformer should be fine, right?? I don't understand why some people run 10A variacs. Seems like a bit overkill??