Tube noob: Little help on the difference between tubes

[Raccio14]

My bass amp is desperately in need of a new tube, but I'm not sure on a couple of things.

First of all, what is the difference between a 12AX7 and a 12AU7? I know that currently, it has an EHX 12AU7 in it, but can I replace it with either?

Also, what would you recommend for a tube itself? There are so many different brands out there that it's hard to figure out what I'm looking at with so little experience.
I'm sure they all have slightly different tonal characteristics, so I'm looking for something with a little bit more bottom end 'oomph' and maybe some gritty warmth, if it makes any sense.

[christw]

How do you know that it's bad? No offense. Just asking because your issue might lie elsewhere.

A 12AX7 has about 3 times the gain of a 12AU7 IIRC. If your amp was built to have a 12AU7 there then replace it with one. However, switching preamp tubes will not make your amp sound very much different besides the possibility of increasing potential for preamp OD/distortion. To save yourself any trouble or woes, just replace it with another EHX 12AU7 if it does turn out to be bad.

[My name is Mudd]

Some general tube info can be found on this page at thetubestore.com

[KramerBassFan]

What kind of amp is it in?

If its microphonic or shorting out thats one thing, but pre amp tubes are different than power tubes.

[Raccio14]

Yeah, i read that FAQ. Didn't help much.

What would the difference be putting in a 12AX7 exactly?

Also, here's the link to my previous thread about amp woes. I'm actually not positive that it's the tube causing the issue. :/
Amp issue, newbie help please! (weird noises)

[Raccio14]

Originally Posted by KramerBassFan

What kind of amp is it in?

If its microphonic or shorting out thats one thing, but pre amp tubes are different than power tubes.

It's an Ampeg BA-115T. One preamp 12AU7 and solid power circuitry. See the last post for my first thread on the issues going on.

[JimmyM]

stick to the tubes they tell you to put in until you learn more about them. some of the more popular brands these days for 12au7's are jj, tung sol, ehx/sovtek...plus you can get nos brands like rca, ge, sylvania, or mullard and telefunken if you want really expensive premium tubes. but for a ba115t, i'd probably just put a new tube in it.

[Munjibunga]

12AX7s are not a replacement for 12AU7s. Buy a high-quality 12AU7. I have a Siemens in V4 of my DB750.