phase inverter/driver tube

[DMace]

I have a blackface Princeton Amp with a slowly dying PI/tremolo tube. It has a NOS Mullard in there now (I think it's a 12ax7, but could be a 12at7, as the prints completely worn off), which came with the amp when I bought it. Any opinions on whether the PI tubes affects tone: much, not all? Basically, I'm trying to figure out whether I should invest in a nice NOS replacement or if a modern replacement will suffice. Thanks.

[JimiBryant]

prob'ly stock it was a 12AT7, I reckon?
what you've got is whatever you've got, though.

I'd say a nice JJ would suit your need if yer watching the cost.
me, I'd get a JJ 12AT7 and 12AX7 from a place such as Eurotubes
and that'll still be cheaper than buying a NOS 12AX7..
(although, really, one can never have too many 12AX7s, IMO)

so, fast forward a bit: you have a new one of each tube, right?
well you plop the 12AT7 in there and see how it sounds and then
try the brand new 12AX7.. better, worse? if you stay with the
12AT7 then you've got a spare of the 12AX7 plus the used mystery
tube which would likely work OK in a pinch as a spare or possibly
even function fine in another spot.. it could be weak, microphonic,
or just plain no good - but it's still worth considering; all of this.

if you like the JJ 12AX7 then you've got a spare 12AT7 which you may
or may not need plus the used mystery tube.. sell 'em on ebay!

[woodman]

FFG lists a 12AX7 as PI for Princeton blackface. personally, i wouldn't recommend an AT there. YMMV. what is the amp doing that makes you suspect the PI tube?

[JimiBryant]

oh, well - if it' s'posed to be a 12AX7 then first I'd try
swapping it with V1 and see what that does.

if the trem works better but the amp sounds yukky,
then the tube is no good.

[DMace]

I should have provided more info in my post: my amp was exhibiting intermittent static/distortion so I took it in to be serviced. My tech said the static/distortion was attributable to the original caps and some grid resistors, but he also said that an osciloscope (?) revealed that the PI tube was on its way out . I only use the amp at home or in the studio so it's not an urgent situation, but I was just wondering to what extent that particular tube affects tone, if at all. Thanks for the responses by everyone.