KA-6006 Hums When Powered On And Shuts Off

I picked up a couple of Kenwood units for a good price, the KA-6006 and a KT-7300. I was really after the tuner and it works fine. The amp is another story.

The amp is actually much nicer than I expected it to be. It seems to have sort of the same build quality as the Supreme 500/600.
So, I powered it on with a variac and when it hit 50V it started to hum. Then, as I went from 50V to 70V the humming got louder and I heard a click and it appeared to shut off (I can't verify if it really did shut off because the power lamp isn't working).

*The DC offset is under 35mV on both channels.

Any thoughts on what might be causing the humming and the click?

Thanks!

Mike

Transformer is probably humming from lots of current draw. Need to rig up a DBT, pull the outputs for testing, and try to bring it up on the DBT with the outputs removed (drivers are tied to the output line, so it'll be fine).

Thanks EW.