Randall 5/15/2018 6:38 PM
Well, that was odd!
Hot Rod Deluxe in for a new reverb tank, input jack and some tubes. I got it done and while the back was still off I played thru it for a little bit. Put the cover panel on, and took it off the bench and into the done pile. Something told me to play it again, and this time no output. I scratched my head and went looking for something obvious, but found nothing. Works when going in thru the power in jack, so that puts it on the preamp. Well, darn back on the bench again. While tracing the signal, I had good strong sine on pin 1 of V1, as well as pin 7, but next to nothing on pin 6. I popped another tube in there and voila! As suspected my tester confirms one side is dead.

Now, what are the odds that tube picked that moment to fail? I mean I realize it is as random as any other moment, but I had just tested it a minute before. Then it dawned on me, do tubes sometimes fail like light bulbs that pop the last time they are switched on from current inrush?
drewl 5/15/2018 7:42 PM
Put it in the socket that only uses half the tube.

V2, wrong half but just kidding.
S- happens.
That's why I always pound on amps, tubes, boards, jacks etc.
Leo_Gnardo 5/15/2018 8:48 PM
Did the defective tube have an open filament? Yes it happens sometimes, on new tubes as well as old. And a tube can just quit working even though the filaments are fine. One of the wonderful quirks of vacuum tubes.

Do transistors ever do that? Or does it just seem as if they do?

Besides having a tube quit, another odd thing for you was having your attention diverted back to an amp that seemed to be working fine. Spooky stuff! You're developing a good technician's sixth sense. FWIW whenever time allows, I put amps thru several warmup sessions plus extended time-on sessions, usually with the radio playing thru them.
Chuck H 5/15/2018 11:16 PM
I probably can't count on both hands how many "coincidences" like that have happened to me with both tube amps and auto repairs. Since you can confirm the tube failure testing the tube pins I'd say you're good. Ordinarily I'd suggest opening the amp back up and checking all the socket pads and such.