Model T getting noisy

[viktah]

Hi,
My 1974 Mod T has been getting noisy lately, even with nothing plugged into the inputs.  The noise comes out of the speaker jacks as well as the line out.  At first I thought it was only on the Brite channel, but its only more noticable on the Brite.  When I crank the presence and treble, it really comes out.  Its kind of hiss-ee and static-ee sound that varies in loundness, randomly.  The tubes are not that old.  I have a schemo and meter, but no o'scope.  I'm wondering what the most likely component culprits would be.
Thanks and Happy New Year!
v

[JoeArthur]

The most likely cause would be tubes - they just don't make them like they used to.  In particular the first tube if the noise and hiss increases with volume control changes.  You might want to swap the first and second tubes around and see if that helps.  Any noise from the first tube will be amplified all through the amp.

The tube socket could be dirty and/or might need the socket pins retensioned.

A cause which has been known to affect some fender amps much more than Sunns is old plate resistors.  These are the 100K values and take more stress than others.  If changing tubes doesn't reduce the noise and hiss, I would replace these next... using good metal film types.

Hope this helps!!

[giovanni]

when i replaced the tubes in my second gen i got a lot of amp noise, adjusted the hum balance and rebiased it... its silent now