I've heard the same thing that you can just take the 2 outer power tubes out to cut the power in half. Don't take that as a fact from me though....

I've actually heard that as a quick fix if you have a 100 watt head and you blow a tube. Just take the blown one and the matched one out and your set with 50 watts. Not sure if it's good for long term use like that though...

Like I said, don't try it b/c I responded here, just letting you know I've heard the same thing...