And one other fact I didn't know until recently, was that the reason that it's not a good idea to play bass through a valve guitar amp, is not due to the speaker, but to the output transformer. Most guitar amp OP transformers aren't big enough (low enough inductance) to cope with frequencies below 60Hz, so the power valves see a near short-circuit at those frequencies and can redplate, maybe burn themselves and/or something else out, or hopefully pop a fuse. At low volumes you are probably going to be OK. but turn it up and especially if using a 5-string and you could be in trouble, even if you are using a valve head into a bass cab.