12ax7 Types

[dougr101]

What does the letter after a 12ax7 tube signify? I see many different 12ax7 tubes....like 12ax7b..12ax7c.

[zaphod_phil]

The 12AX7A is an improved version of the 12AX7. I forget what they improved, but a 12AX7 is apparently the same as an ECC83, under the European tube naming system. After the "A" various tube manufacturers put extra letters to indicate things like variations in gain, or lower noise, etc. These extra letters seem to mean different things depending on the manufacturer.

[blaren]

I dont know much yet but....the first number is the volts? 12ax7...12=12V ?
a 6L6, 6V6, 6BQ5, 6CA7...I presume 6=6V.
Dont know (I think I KNEW but forget) what the letter means (A) in a 12AX7...or L in a 6L6.
The X in a 12AX7 is the gain factor...like a 12aX7 has a gain factor of 100%. A 7571 has 70% (dont ask)..a 12AT7 has like 60% gain factor...a 12AU7 has 50%.............. (the percentages I'm "qouting" might be off but you get the picture).
I too think that the 12AX7A is a "higher grade" 12AX7. Quieter, less prone to microphonics??.....Dont often see the final "A" designation on Euro 12AX7s...oh, and ECC83 IS the same as 12AX7 but it's the European designation....but a lot of Euro tubes will have both... "ECC83/12AX7" on them.
I think a 12AX7A is a lot like a 7025 which IIRC is like a military version of a 12AX7 but not Army or Navy, otherwise it would be a "JAN" (joint army navy) ...SO....I guess if a 7025 really IS a military 12AX7, it was only for the Army and Airforce????lol Oh...then there's the Euro designation for military 12AX7s which is a CV4004.
Then the Euro designations for the other gain factored 12A-7 tubes like 12AT7=ECC81 blah blah blah
GOD...you confused yet? I sure am.
Dont even ASK about EL34/6BQ5,7189,7189A, those Russian version..6P14P or whatever....
Good thing there are only a couple of manufacturers left or I'd have a melttdown.

[rjgtr]

I think the european equivalent of the 12ax7A is the ECC803. In power tubes they designate a 'better' version by moving the second letter to the end. A better EL34 is an E34L.

Alas these days a 7025 is really pretty much the same tube as a 12ax7. In the old days they were slightly lower gain 12ax7s chosen for noise and microphonics.

Check out this site for some info on what all the letters mean - http://www.octave-electronics.com/cus_l ... info.shtml.