I just picked up a Hammerhead combo and wanted to try different tubes that I had laying around. I know the amp is fixed biased but since I wasn't sure of how well my tubes matched I still plugged in my bias probe to check on this. When I checked the first pair (Mullard Reissue) I got 60mV / 65mV and the second pair (Groove Tube) I got 65mV / 69mV. The plates were about 360V. I've never biased EL34s that high and I was wondering if it just read that high because it is fixed biased and perhaps my probe wasn't measuring the same way it would with other amps....or.....the tubes just run too hot in this amp?? It sounds great and there are no weird noises. What prompted me to post this is that I just popped in a new pair of GT EL34Ms and there is a burning smell coming form them. They aren't glowing abnormally, but the smell combined with that high bias had me concerned.