fender hot rod deluxe ot advice

[The Dude]

If the tube key broke off and the tube was installed incorrectly, there may have been excessive current from B+ through the OT and through the incorrectly installed tube. It certainly appears the OT was stressed. Hopefully, that's the end of it.

[The Dude]

FYI, I always stock a few of these for just such an occasion.

https://www.cedist.com/products/keyw...ce-octal-tubes

[Helmholtz]

so a friend tried to bias this amp using an (under-tube bias tool). he snapped off the aligment pin and presumably plugged the tube in with the wrong pin orientation....i then relaced the screen resistors and the diodes cr 4 and 5, then replaced with new 6l6gc and biased using the supplied bias test to around 60ma. the amp sounded great, we played for about 30mins and he took it home and played for 3x3 hour sessions. then the amp blew a fuse. he brought it back, i replaced the fuse and the amp made a hideous hum and blew the fuse....
i tested dc resistance on the ot primary and found one half to be open, the replaced the ot.....

I didn't get that the above actually is the old story about the original OT.
Sounded like a second OT failure/accident to me.

[g1]

the amp drew about 50 watts at 103v(the limiter drops the voltage)....

You should not be on the limiter anymore. It may give you false idle current (bias) readings, and will compress peaks, so the amp will not be getting a real world work-out during testing.

[georage]

thanks G1. actually. the dim bulb drops the voltage a lot and i noticed that about 5 amps ago...so now i bias one under the dim bulb and make sure its not going to short then re bias without the dim bulb. there may have been a few amps get by with hot bias, but i generally bias cool, so not too worried.

[georage]

Dude...this guy brought in another amp and both power tubes also had broken-off aligment pins! hes rough on tubes! your tip is well recieved! and thanks again helmoltz.
so the new ot went in and performed flawlessly. the amp sounded great and went back to the owner. i can only assume that the original ot was so stressed that it failed eventually under normal play...if it fails again, it will be completely unexpected and out of my capabilities.