The last forum-members jam we had in 2019, I brought my beloved tweed Bassman, plus one or two "backup" amps. Foolishly, I had it sitting straight up in the trunk. Sadly it fell over and stopped working. Testing all of the tubes individually, they all checked out, and they all came "on" when power was applied, but no sound whatsoever. I suspected the jarring might have played havoc with the standby switch (standby-switch failure would get you tube-glow but not sound). This morning, I finally replaced the standby switch, plugged in a set of TAD power tubes, and I'm good to go.