65' Fender Twin - Help Needed Troubleshooting

[Chuck H]

You don't have to be psychic to read and pay attention to the question.

No. But you do need patience and an attention span longer than a camera flash. These virtues almost qualify as super powers in the modern world.

[Tom Phillips]

... there is an audible hiss present. ...

It is always difficult to evaluate a problem like this via a discussion group because we can’t listen to your amp. On person’s “excessive hiss” is another persons “normal operation”. Right now we don’t know if your amp is malfunctioning or is performing within normal parameters for that model. If you could locate a buddy with the same, or even a similar model, amp and do a side by side test you would be in a better position to answer that question. Can you arrange that? Maybe you have already determined that your amp hisses a lot louder than other ’65 Twins but your first post doesn’t explicitly say that.
Regards,
Tom

[Chuck H]

I would back up Steve's post at this time. I only know from reading, not experience, but the early Bassman reissues had trouble with hiss because of the plate load resistors. Could have been the same for the '65 Twin.

[J M Fahey]

On person’s “excessive hiss” is another persons “normal operation”.

There's a famous scene in one of Woody Allen's movies where he and is wife who are about to divorce visit a troubled couples Psychologic counselor, who asks the classic: "how often do you make love?"
Woody answers: "I can't stand it, almost never ..................................... 3 times a week"
and she answers:
"it's unbearable, all the time ..................................... 3 times a week"

[acorkos]

If you could locate a buddy with the same, or even a similar model, amp and do a side by side test you would be in a better position to answer that question

or swing by guitar center or sam ash or similar store