What is V1 and V2 on the 12xa7's?

How do you know which tube is what?

What is V1 and V2 on the 12xa7's?

Not really sure, I don't recall seeing those on mine, but they could be there, I have work soon but I'll check after work and tell you if they're there and what they seem to be for.

How do you know which tube is what?

EL84 = Tall, has a metal plate under it held by springs if I recall the design right. 12AX7 = Shorter and more of them. There's also a diagram on the inside of the amp on the left side, looking from the back of the amp.

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Usually V1 will be closer to the Insert Jack on the amp

and V2 (or V3 or V4 depending on how many preamp tubes an amp has) will be closer to the Power Tubes.

If you think about how your signal passes through the various points in an amp that will make more sense.
So does the blues jr have v1, v2, v3, el84, el84 ?
( There are 3 x 12xa7 and then 2 x el84 )

What's the diff btw v1 v2 v3?

^yes that is correct.

Well, I'm not a Blues Jr expert so maybe someone else can chime in. I looked at the owners manual online at fender.com and it didn't really help except to confuse things by mentioning the amp has 3 and then 4 preamp tubes in different sections. I'm pretty sure the current ones only have 3. The earlier ones may have only had 2 - not sure.

Generally, with preamp tubes the tube itself is split into 2 parts (kinda like having 2 tubes in one if that makes sense). V1 would typically handle your gain (and clean channel on an amp that has a clean channel) with V2 just being a second gain stage. V3 (or the last preamp tube in most amps) would be the Phase Inverter - which is just a fancy way of saying it feeds the power tubes.

Your best bet if you really want to dig into this is to surf/post in the fender.com forums. Lots of knowledgeable people over there and I'm pretty sure they have a dedicated Blues Jr thread.

Why are you asking. Do you have an issue or are you just curious?
Thanks. Will look at fender forums.

Just looking at new tubes and wondering
how it works and which tube does what.

So do you use the same brand and
tube for all 3 of the 12xa7 tubes?
No. Actually, I recommend NOT using the same type and brand. Different manufacturers have slightly different flavors (cleaner vs darker and/or brighter vs darker).

Again, I can't speak to what works best in Blues Jr for a particular flavor.

You can also experiment with 12AT7s in addition to 12AX7s, the former having less gain generally. My suggestion is to contact Doug at dougstubes.com. Send them an email with what you have an what you want. Great outfit and great response times.

I recently got these from them for my Valveking:

Tung Sol in V1
Penta Labs 9th Gen in V2
JAN Phillips 5751 in V3

good luck...