I recently acquired a used Hughes & Kettner Switchblade 100 watt head. I'm using it with its 8 ohm output connected to my 8 ohm THD Hotplate connected to the 8 ohm input of my Mesa 4x12 cab.

The first week I had it, everything was fine. Now, however, it blows a fuse after a few minutes of play. I have repeated this 3 times. If I take the hotplate out, the problem doesn't occur. So, it's easy to blame the hotplate, but this same hotplate has worked fine with countless other amps. And, I have *another* hot plate, this one is 4 ohms, which I connected to the 4 ohm output of the Switchblade and into the 4 ohm input of my 4x12 (turning it into a 2x12) and the same problem happens.

I've tried different cables, etc. I even went as far as to replace the power tubes (put in Mesa EL34s).

What's interesting is that when the fuse blows, the entire amp is still on, and the tubes glow; there is simply no sound. Though my tuner still receives sound from the fx out (which in my mind makes me think the preamp tubes are working fine).

Any idea where to go from here? All the local amp techs seem like idiots, they don't even know what a hotplate is.