Matched triodes for v2

[neon333]

Is it really necessary to have matched triodes in the 12ax7 going into v2?

[dgately]

Is it really necessary to have matched triodes in the el84 going into v2?

Do you mean matched triodes in the 12AX7's that go into V2? If you ARE talking about the PhaseInvertor (or 'PI' which is usually V2, but not always), it's a 12AX7 (or a variant) and having a matched tube (V1a & V1b sides), since it is really basically two tubes in one, means both sides should give = results.

It: A) can't hurt! B) is a personal choice!
I'm finding that my a & b sides in my 18Watt TMB's PI are fairly close in voltages and I never really bothered to make sure that the sides were matched. My scope tells me that they both seem to put out out-of-phase but equal looking signals...

If you are looking to buy tubes and can find matched dual-triodes at a decent price, why not?

dgately

[neon333]

Yeah, I just edited my original post. I meant the PI 12ax7. Oops

[kd]

I think you meant 12ax7 and the answer is no. I think the bit of mismatch normal in the triodes of a 12ax7 just add to the tolerance mismatch stack up that occurs in an amps components, each contributing to the tone you get from the amp. Just my opinion.

Ken

[zaphod_phil]

A degree of imbalance in the PI/power stage of a guitar amp is preferable to allow some sweet even harmonics through. This is not the case with hi-fi amps.

[dgately]

Yeah, I just edited my original post. I meant the PI 12ax7. Oops

A simple mistake (I make them all the time!)

After reading his response, I would have to agree with Phil that a little miss-match is good

I was thinking more that the PI is basically driving the EL84s which should be matched. But then again, the PI in the 18Watt appears to add quite a lot of gain and does enhance to the overall tone. Why not add some "harmonic details" as well via the PI. I guess I would want to understand how having equal halves (above and below the reference) of the signal differing by more than "just a little"...

As I said, it's really a personal choice.

I plan on purchasing at least one matched dual-triode for testing!

dgately

[zaphod_phil]

It's also very debatable as to whether the EL84s should be matched. The great vintage amps that we try to emulate, including the Marshall 18W, never used matched tubes. They just pulled the power tubes out of the box and stuck them in. Then Groove Tubes started marketing hi-fi style matched tubes. Again, a slight mismatch will make for a sweeter tone. However, if they're too far off and hum will increase, or you could even get one of the pair redplating.