12AX7 pre-amp tube orderÉÉ

[Jared Purdy]

If you are running the same tubes in the pre amp section (all three being Tungsols), does it matter what order you put them in?

I picked up a set the other day to keep as spares, and thought I'd check them out to see if I can hear any difference in sound from the JJs that are in there now.

When I bought them the other day, the tech numbered them 1, 2 & 3, and was sure to point that out to me. And, if they should be put in that order, which socket is 1

Does it matter with all 3 being the same?

[MWJB]

V1 is the first tube in the chain (input tube), this will be the preamp tube farthest from the power tubes, irrespective of whether you are counting from left to right, or right to left. V3 will be the phase inverter tube (PI) and is closest to the power tubes.

As all 3 sockets use a 12AX7, in theory any of the 12AX7 tube you have can go in any of the 3 preamp sockets. However, if you notice a deteroration in performance/tone, or an increase in unwanted noise (some sockets are more noise sensitive and require a tube with low microphonics), that pertains to a particular tube in a particular socket - then remove the tube from that socket (perhaps your tech has already done this?). Otherwise, there is no technical reason to keep the tubes in a particular order. What sounds best is best.

"Does it matter with all 3 being the same?" Well, they're possibly not "the same", they were only made in the same factory & have the same brand & designation...you may still notice a degree of variance between them, just as you would notice differences in manufacturing tolerances with any other product.

You wouldn't expect apples from the same tree to be identical would you?....except tubes don't grow on trees...& apples aren't made in factories (yet)...OK, OK it's a bad analogy, but you get my drift? :-)

[Jazz P Bass]

12AX7 tube placement

It could be argued that the tube with the best hum canceling abilities should be in the first socket.
This also applies to reverb recovery tubes.
The PI tube "should" have the best plate to plate matched characteristics.

[MWJB]

"The PI tube "should" have the best plate to plate matched characteristics." Indeed, it can't hurt, but even in a typical LTPI the tube would have to be seriously mismatched to have a noticable effect (I have never come accross such a tube). Jared didn't mention it, but his amp is a PV C30, which has a cathodyne PI and doesn't require any matching of triodes as only one triode does the inverting.