My Princeton Reverb doesn't hiss.....

[clyde]

....however it has a slight "sshhh" when playing F# to B on the bottom two strings, the A and the E.  This weird artifact sustains longer than the note then dies.  It doesn't do it on any other note on the neck, and only after the amp warms up.  I'm sure it's in the power supply but just had to post for interest's sake since it seems to be Princeton Reverb week here on the forum.  Tube amps can be pretty bizarre. 

[tubeswell]

tube swap?

[Ed_Chambley]

I guess I am the cause of it being Princeton Reverb week. 

Tubes first as mentioned.  Most problems are tubes.  One of the best things I have found in a Princeton is adding another 20uf filter cap or just get a 40/20/20/20 multi-cap, stiffens up the bottom some.  There are many other things people do, but it makes a change in the sound of the amp.  fenderguru.com has some good info on Princetons.

It is strange how things happen.  Last rush of repairs were Bassmans, but I did end up with a early 62 Brown Bassman and it is nice.  I am quickly growing tired of Princeton hiss.

[HotBluePlates]

Can you plug in an extension cabinet into that amp? I'd be curious to see if it is a speaker/cab problem that only appears on those low notes.

[clyde]

Funny you should mention that as I did plug another amp into the Princeton speaker, no buzz.  However I didn't try an extension speaker, until you suggested it.  No buzz.  It seems to be a microphonic 6V6, which when held (with an insulating pad), stops the offending noise.  Good call HBP and Tubeswell. 

[HotBluePlates]

Sweet! Glad the resolution turned out to be pretty simple to fix!