How do you know which brand pre-amp tubes?

i read about people selecting different brands and different A*?*7s for different sockets
how do know what to use where?
and if i have to play my 50 cal + at living room levels, is selecting pre amp tubes going to make a difference?

if the designer specify to use 12ax7, use them. You can try using other 12xx7, but it won't be the same... and it won't damage you lovely tube amp.
If you play alone at bedroom levels, you can notice some nuances using different brand tubes.

crguti said:

if the designer specify to use 12ax7, use them. You can try using other 12xx7, but it won't be the same... and it won't damage you lovely tube amp.
If you play alone at bedroom levels, you can notice some nuances using different brand tubes.

Click to expand...

but i've read that some manufacturers 12ax7 are different from others and produce different results

yeah, there are some differences, but it isn't noticed at gigging volumes, not when you play together with a drummer and bass.
Try it, difrerent brand tubes change a bit the EQ of the amp, but it isn't as big as using an eq in the loop, for instance.

For the 50 Cal+ use a 12AT7 in the reverb socket, which is V4, the fourth closest tube to the input jack.
(V1 is the closest to the input jack.)
All the others are usually 12AX7s.
Here's a quote from the manual, available at the Mesa website:
MAINTENANCE:
Excessive noise, feedback, squealing or rattling sounds coming from the speaker
are almost always the result of a deteriorated 12AX7 preamp tube, usually the first (“V1”) or the
second ("V2") tube on the right (as seen from the rear), nearest the input jack. Checking the preamp
tubes in a tube tester is almost useless. The best procedure is to substitute a tube that's known to be
good and noise-free in each possible tube location, one at a time. Here are some clues to speed up
the process: if the problem appears only in the Lead mode, then the culprit is probably V1, V2, or V3.
(V1 is the tube nearest the input jack; V2 is the “next one out”; etc.) If the problem is in the Rhythm
mode only, then V2 is usually the problem. If the reverb is noisy or has some other problem, replace
V4. (Unlike the other preamp stages, V4 requires a 12AT7-type tube.)
Sometimes the insides of the power tubes themselves can be heard rattling. If the power is weak and
your tone is flat, try replacing the larger power tubes, type 6L6GC. We strongly recommend using
only genuine MESA tubes; in fact, your amplifier's warranty is not valid if you use other brands or
types. Power tubes are like guitar strings; they begin to deteriorate as soon as they're put into use.
You may notice improved performance by replacing the 6L6’s, every few months, depending on
usage.

But do not change the 12AX7 or 12AT7 preamp tubes unless a specific problem arises. Their
aging is very slow and you won't likely hear any improvement by changing them unless one has
become noticeably noisy (and in fact you may even incur worse performance if you change a tube
that's currently working fine).

Many will disagree with the last paragraph, mostly because it can be fun to try different brands, and many feel the older pre-amp tubes sound better and actually last longer.
Go to the "Tubes" sub-forum to get started.

+1....

There is lot of really good info posted in the "Tubes" sub-forum. I know I learned a lot there! :mrgreen:

Try different ones. Be careful I started small ....Heres part of my collection. It got much bigger after this photo....lol! Bob

Wow...Bob!

Is that really a collection or is it just a result of your therapy!

Awesome, man!! :mrgreen:

rocksalt7 said:

Wow...Bob!

Is that really a collection or is it just a result of your therapy!

Awesome, man!! :mrgreen:

Click to expand...

Obsession is more like it! lol! I have 500+ old stock 12AX7's.Bob