just saw a related thread and was curious the answer as well. i have an engl fireball 100 and dont know what output i should be plugging into - what are the problems if im using the wrong output and which is the correct one?
Hi tom
Best case - The amp runs a bit hotter and you reduce your tube life
Worst case - Output transformer blows, basically means you have to get a new amp.

Find out what impedance (ohms) your cab is, it should say on the plate where the cable plugs into the cab (it may also have a switch for mono/stereo. If so, set it to mono and use the corresponding input) Whatever the cabs input is, that is what you should set your heads output too.