Improper switching between pentnode and triode

[bfglp]

Marshall recommends being in standby mode for adjusting the 1/2 power switch on their amps, what would happen if frequently misused?

[Mars Amp Repair]

Hello bfglp,
Hmmm...I'm thinking of a couple of possibilities...1: The switch would be more likely to arc internally with B+ on it when the contacts are all momentarily all disconnected when the switch is thrown.
2: If there is a voltage spike created by throwing the switch, that could technically be some damage to any solid state devices in the amp.
Other than that, I have no suggestions as the tubes would be cut off with no screen voltage on them.

[mhuss]

If the switch changes PT windings, doing so while current is flowing is bad for arcing, etc. If it's a 'triode mode' thing, I don't think that switching the screen grid connection while live would be good for the tubes.