It depends on what resistance it is rated for... I have a Fender Bandmaster rated at 45 watts into 4 ohms, so that equates to about 30 Watts at 8 ohms, (doubling the resistance yields about 2/3 the power... probably not exact, but close enough for rock 'n roll!!)
By just about every maxim laid out on this site, this head paired with a 1X15 cabinet should not be enough to gig with, yet this has become my main rig, replacing my V-4 as the first call... Granted, the two bands that I play in have sane musicians and play at reasonable levels

By cutting the bass slightly and boosting the treble, I get a super warm tone in the room that is rapidly becoming my reference...
As for the circuitry, if it doesn't seem right, have it looked at by someone qualified to repair tube amps... I have a guy that I trust, so I never worry about my stuff... When it needs fixing, it gets fixed

I don't know what year the Bandmaster is, (early 70's I'd guess... It's definitely seen some
hard handling!), but after passing muster at the shop, I'm confident... I still, (and always will), bring a spare head to every gig!
-robert