Maybe easier in most amps, but I've got a Fender Super-Sonic which has two circuits, one based on the Vibrolux, the other on the Bassman. I've been driving the tubes real hard (in the Vibrolux channel) for my overdrive for the last 6 months using a power attenuator. I don't use it anymore and I've got these extra 12ax7s laying around and I figured I'd do my amp a favor and at least swap out that first one I'm driving so hard...uh but I can't tell which that is.

The diagram inside my amp has the tubes labeled V1, V2 (and so on, I'm assuming for Valve 1, Valve 2...) with the 6L6s at 6 and 7 (or 5 and 6? I forget)...and...well I don't know whether it's different for the Vibro/Bassman channels, this thing has 8 preamp tubes or something like that. I think the one 12at7 is for the reverb?...or....guys I just don't know. I just wanna drop in a new one, they're a couple old NOS tubes, wanna see how they sound compare to the newer stock ones...get a fresh one in there I know won't crap out anytime soon...

Any ideas? How can I tell?

Generally speaking, both the phase inverter and reverb driver in most Fender heads use 12AT7s. Not being familiar with the Super-Sonic nor being able to find schematics or info after a brief search on the web, it would be fairly difficult to ascertain which tubes corresponded to which channels.

Hm, is there anyway I can troubleshoot it? Like remove a tube and see which channels do/don't work? Can that damage my amp?

Or like...something?

???

Plus I wanna over time here get to know these things about my amp so after the warranty runs out (or, say, emergency on road) I can fix the real basic shit myself.

usually V1 is the one closest to the inputs and furthest from the power amp section.

the only way I'm aware of to know for sure which tube is which (assuming someone tore out the tube layout chart that Fender amps always have in them) is to open it up, taking care to not get electric shocks, and see which tube is connected to the input jacks.

There's not necessarily a reason to think that V1 is seeing more abuse than any of the other tubes. And with a power soak type thing, it's the output tubes that are being burned up at an extraordinary rate, not the preamp tubes.

Thanks, that helps pinpoint it a bit better. The tube layout in my amp goes:
12AX7WC (x5)
12AT7
6L6GC (x2)
12AT7
12AX7WC

The first three preamps are front left right next to the input and the second three are back right which makes me wonder a little. I read somewhere the V2 is actually the preamp for the clean channel (both of them I guess?) and V1 and 3 are for the dual cascading dirt channel. I'm guessing the 3 valves after the 6L6s are the tubes I wanna replace, so I'll replace the two 12AX7s and track down a good 12AT7 when I've got the dough (totally broke and in debt right now, shiiiiiiiiiit).

Aso, what's the deal with re-biasing?

Thanks everyone for helping out a know-nothing doofus.

scott wrote:There's not necessarily a reason to think that V1 is seeing more abuse than any of the other tubes. And with a power soak type thing, it's the output tubes that are being burned up at an extraordinary rate, not the preamp tubes.

i think scott is right about this. if you do still want to find which preamp tubes go to what, i would try this (and a little disclaimer here, i could be wrong ) :

turn the channel without reverb up to a moderate volume and the other channel all the way down. tap on all the preamp tubes lightly (that is to say, with a good tap, but not enough to break anything) with a pen (or something plastic.. probably doesn't matter, but better safe than sorry). the preamp tube for the channel you have turned up should sort of amplify the sound of you tapping it (or possibly make some pretty weird noises if it's a bad tube.)

that's what i would try if i were trying to figure it out... but i'm still learning!