what are usually the best settings for volume on a tube head or amp (specifically a 5150), for recording and performing? Also, are attenuators worth getting?
Actually the best would be to have the amp cranked to the level where it's sweet point is... of course this isn't always possible, so you have to compromise....
Attenuators can be handy to turn your amp down a bit, but they still won't turn your 100W Fullstack into a bedroom device... at least not without massice tone sucking
On a 5150.. no. there is no master like you're speaking of.
With something like a JSX or XXX, though, I'd try to keep everything at noon (level wise). I wouldn't put the preamp volume past noon at all if at all possible.
I have used my 5150 with my last band a fair bit.... Inside in small bars i found 3 was overkill! I played a few outdoor gigs and had to crank the Rythym to 4 and the Solo to 5 as i was not mic'd thru the PA.... the amp was more alive but no where i've played inside would i get away with a 5150 half stack on or near halfway! But when you get a chance to open a 5150 up it is an experience!!!!!