long plates or short plates, what is the difference?

[jcr1234]

Often I hear 12ax7 type tubes described as long or short plates. I can see some plates are longer than others, why is this important and what effect does plate length have on tone?

[kyoungsteadt]

The shorter plate models are less prone to microphonics and tend to work better in combo amps. Either plate type would work well in a amp head.

[dotfret]

Might also add that the longplate designs tend to be older, pre 1962, although some factories made then after that - Ei were still making longplates into the 21st century, and there are others.

It does depend on the amp, but long plate designs tend to break up earlier and more smoothly than short plates, which might also be why they go microphonic easier ...