Originally Posted by DragonSarc
and just would like to add make sure that the amp is always lower than the cab if 1 step mismatching ie 8ohm amp to a 16ohm cab not the other way around
For a SS amp this is instant death.
On a tube amp this may seem to make sense on the surface, as a shorted output will not kill a OT right away so too low on the load might seem to be harmless, but in reality this is not the case. Unless your OT is spec'ed above its normal operating parameters (as the JVM and Mesa amps seem to be), you should never mismatch in ANY DIRECTION.
Marshall amps, especially older models, are a bit like vintage Ferraris: they work well within their designs but have a low tolerance when you nexceed them.