A balanced view

Balanced pairs of valves. Do you need them? the simple answer is, no you don't.

What does a balanced power amp section in a valve amp offer the guitarist? Less hum.

What do unbalanced ouput valves give you? A bit of even-order distortion - yes, they can sound better! And a bit more hum. Too far out of balance and you start to lose the handy humbucking function of the push-pull pair.

Your output transformer isn't balanced - it's only worth doing that for hi-fi - so why bother with balanced pairs of valves.

Sometimes hum really matters, and in very powerful valve amps imbalance can lead to instability. SVTs are a good example - with six power valves in push-pull the differences can really add up, and if you have a later one with the little red and green bias lights it will be hard to set up without balanced sets of valves.

Silverface Fenders often have a hum balance control which allows you to balance the bias voltage between the two push-pull 'sides'. Works a treat, you can stick in any old 6L6-es and dial the hum right out. Set the overall bias with the resistor that goes to earth on the pot body from the wiper (centre of the three tags), if you need to. Some people remove this really handy little tool when 'blackfacing' a silverface amp and convert it to a bias adjust pot, thus making willing victims of themselves for the eager sellers of matched valves. But I like it, he added redundantly.