12AX7 gain test

[nigelwright7557]

I have never really got on well with the 12ax7.
I find I have trouble getting rid of noise.
It needs great care especially if concatenated.
Both halves of the valve need decoupling separately.
Most of my designs use the 12AU7. It has less gain but is easy to manage.

 

[Lingwendil]

I don't like the 12AX7 or 12AU7 for much more than guitar amplifier applications. I find that the 12AX7 takes too much work to perform well for low distortion... and the 6N2P or 6SL7 will work much better in their place, albeit with lower gain. The 12AU7 usually ends up a cathode follower to be useful when I have to use them. The 6CG7, 6SN7, or 6N1P are much better choices for applications that need similar gain and lower plate resistance.

 

[DF96]

Cathode bias is negative feedback for DC, which means that it essentially "hide" some difference between the tubes under test.

But grid leak bias varies quite a bit from valve to valve, so is a poor way to compare them unless you intend to use this bias method in the actual circuit.

12AX7/ECC83 is fine when you want high gain and low distortion and are prepared to do a proper design. If not, use an easier valve.