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Power Tube Mismatch to make the amp your own

shatteredsquare

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Back in choir days, there was a term called something along the lines of "key fatigue"... where after you've been singing in one key for long enough in rehearsal, your mind sort of gets numb to that key. People start wobbling off pitch, it gets hard to tune with another section, things start to sound less than stellar.

The fail safe way to fix it at that point in rehearsal was for the director to change keys, either up a half step or down a half step. All of a sudden the same passages you've been working on all sound fresh, your ears can easily pick up on pitch subtitles that were before mushing together, and it's easy to tune in with the other sections.

I'm not sure what the power tube mismatch equates to at 0.00, weather or not they are 'perfectly balanced', as in mathematically identical, or just 'within tube factory tolerances.' What I do know is that if you bump power tube mismatch up or down by just a little, 0.10 or 0.20, up or down, it makes enough audible/tangible difference as if to take the amp from the territory of being a "model of a reference amp", into the territory of "Cliff C. traced the circuit of a Dual Rectifier I bought from a guy on craigslist."

Going past +/- 0.30 in either direction does start to degrade the sound a bit...it can handle going down past -0.30 ok, but going up past +0.30 sounds like...logically, it's time to buy new tubes. But between +0.30 and -0.30 there is so much available subtle variation at increments of 0.001, that effectively make the amp...if they were on a shelf in a studio next to each other, all with the same circuit...a different amp.

+/- 0.30 in either direction from zero amounts to no less than 600 (SIX HUNDRED) variations of naturally occurring real world amplifier tonal variation. It is subtle....if you can't tell a difference, I'm wrong. Don't use zero, your amp is in there! :D

somebody help me with math, how many thousands are in .300
 
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APOGEE123

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I agree with you on small Increments. I’m really blown away by all the tone variations you can get and in many blocks. It’s like tone down to the atom.im really enjoying it.
 

200man

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I used to mismatch tubes and got very interesting results.
This though would be different because we can select output tubes and mess with bias adjustment but I don’t remember being able to use different tubes on opposite sides of the signal for a push/pull amp type.
 

shatteredsquare

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I don’t remember being able to use different tubes on opposite sides of the signal for a push/pull amp type.
It's not combining different tube types, I think it's supposed to the be modeling the variations in manufacturing tolerances of the same tube type.

Like Mesa Boogie tests their tubes and sells them as matched pairs with hot/cool color labels, red/yellow/etc. The mismatch parameter I guess is just modeling the difference in physical and electrical tolerances between the power tubes, so one tube feeding into the next is not an exact mathematically modeled copy of the first one...you start getting more interplay / interaction between their distortion / sound characteristics as you get away from zero in either direction, since (from the manual, pg. 60), 'A value of zero represents perfectly matched tubes.'
 
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200man

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It's not combining different tube types, I think it's supposed to the be modeling the variations in manufacturing tolerances of the same tube type.
That’s cool, I understand...studied h parameters, semiconductor curve tracers and spice simulations in college. No, I was just trying to say that musicians messing with different tube brands often yielded interesting, sometimes quite musical results.
 

lqdsnddist

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That’s cool, I understand...studied h parameters, semiconductor curve tracers and spice simulations in college. No, I was just trying to say that musicians messing with different tube brands often yielded interesting, sometimes quite musical results.
For sure. I remember with some of my old amps just grabbing what myself or a buddy had laying around with the right pin layout to fit.

We, or at least I, didn’t have any idea about “matched pairs” etc. Heck, didn’t even know about NOS and I could of grabbed an old RCA as likely as I would a Chinese tube. Didn’t have Internet forums to read, know what was good and bad etc.

It was just a question of did it power up, did the tube burn up quickly, how did it sound, ya know. Had no concept of trying different types in different positions etc.

Likely had some winning combinations and some poor sounding ones, though I would of had no real idea why it sounded good. Musical aesthetics of tone can be funny like that lol.
 
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