Hissing and Popping Bassman

[centuryx3]

My '64 Bassman (AA864 Circuit) is driving me crazy. I recently had caps replaced, and new power tubes, and a general going over. All was great for abut 3 months. Now it will hiss and pop intermittently after an hour of playing. Really loud hissing. I have one AX7 that I know to be good in my Twin Reverb. I take it out and substitute it one at a time for the AX7 tubes in the Bassman. No improvement. I am considering ordering a set of tubes and replacing all the preamp tubes. Any thoughts?

[Prairie Dawg]

My '64 Bassman (AA864 Circuit) is driving me crazy. I recently had caps replaced, and new power tubes, and a general going over. All was great for abut 3 months. Now it will hiss and pop intermittently after an hour of playing. Really loud hissing. I have one AX7 that I know to be good in my Twin Reverb. I take it out and substitute it one at a time for the AX7 tubes in the Bassman. No improvement. I am considering ordering a set of tubes and replacing all the preamp tubes. Any thoughts?



If they're original, the plate load resistors are likely suspects.

[Baxtercat]

here's just one humble FWIW:
Make sure it's stored in a dry environment....not kept in a basement, etc.

[Blue Strat]

Yep, preamp tubes and 100K plate load resistors are the first suspects.

See if you can pin it down to one channel by using the volume controls.

[Roe]

i prefer using 1w ab cc plate resistors like the silverfaces did

[solitaire]

Bad contact in the valve sockets?