Do small preamp tubes 12ax7 need to be matched?

I have always been told that matching only matters for the power (output) tubes but I think it would depend on how the circuit is done. I think the Aesthetix are balanced right? Maybe it can make a difference in that case. See if you hear a difference!

I think "matched pair" for small signal tubes is a misnomer. What, exactly is being matched? Transconductance and current figures are a poor indicator at best as to how any given small signal tube will perform in situ. Anyone with extensive tube testing and utilization experience would agree that sometimes even tubes that read NOS on a calibrated tester can be absolute duds sonically be it noise, microphony or other sonic issues. My strategy is usually to find a half-dozen tubes that all test good, and then listen to all of them to find a good sonic match for a useable pair. Generally, I find that of the half-dozen, at least two will be unacceptable for the given application (which doesn't preclude their use elsewhere in a circuit). Hence, the old saying of 'if it sounds good it is good', applies quite well to small signal tubes. Power tubes, of course, are an entirely different story.

-Richard

I have been told that the small signal tubes do not need to be matched but that the power tubes do unless you can adjust the bias on your amp.

Chuck

Palasr is correct on all points.

I would only add that perhaps the bigger issue is whether to bother with (i.e., pay for) tubes that are "low-noise" in the context of preamps. While it obviously depends upon the preamp, my experience is that low noise is not a necessity for line stages, but that for phono stages, it is very important.

The only small signal tubes I closely match are ones used as long-tailed phase invertors. Most amps don't have any provision to adjust the AC balance of the driver stage. For that I use a VTV small signal tube tester. It also lets you listen to the tube so you can check for noise and microphonics. Very helpful if you need to screen alot of tubes.