I have an old 60's Japanese head (looks like a blackface Fender) that I'm not sure of what the output impedance is. I remember seeing 4 ohms being printed on the output transformer. I talked to a tech and he said it'd work well with 8 ohms (something about there being stereo outputs or something, I don't remember). Anyway, assuming it is meant for 8 ohms, can I use it with a 16 ohm speaker? I wouldn't be cranking it if that matters (no higher than like 2 or 3). What if the output impedance is 4 ohms?