How important are matched triodes in a 12ax7?

[jcr1234]

One of the 12ax7's I have is an Eico branded Mullard where the triodes measure 900 and 1150 on my Hickok 533a. Are these numbers kind of low for a 12ax7 and indicating that it is near the end of its life? Also, how close do the triodes need to be?

[rjgtr]

I'm not sure if the values matter. Judge the tube by how it sounds.

As for matched triodes, the only place it might matter is with the phase inverter and even then only in a Hifi amp. In a guitar amp it isn't as important as long as the over all sound is good.

[zaphod_phil]

+1

There's no benefit in having the triodes matched in a guitar amp, assuming they're not failing.

[StarGeezers]

First time I ever heard that brought up .. never a concern before ...

[jaysg]

First time I ever heard that brought up .. never a concern before ...

I think some of the audiophiles go trippy on this one.

I don't have a selection of hi-zut tubes, but I was impressed when I beheld an old telefunken 12ax7 swapped into the PI of a Trainwreck Rocket. The amp went from ho-hum to desireable.

[StarGeezers]

Jay , I hear ya'... those audiofools are just crazy Lot of stuff they hear off the internet ... we know about that eh ???

BUT I do have 3 old telefunken 12AX7s that I DO particularly like the sound of ... especially in the PI as you say ...or anywhere really ...

[hotair]

For the most accurate reproduction you would use close tolerance parts and matched pairs in differential circuits to cancel out as much of the even harmonic distortion as possible. In our case we like distortion, in fact many like the phase inverter to be a little unbalanced to get some second harmonics introduced in the signal. Strangely enough we like distortion. Power tubes benefit from being matched to reduce the unbalanced dc current through the output transformer.

I have a couple of matched small signal tubes and other than them being NOS and should sound sweet it is not the balanced nature that concerns me. More that they are a quality tube. Got them free though, would not have paid any extra for them.