Balanced triodes in PI of Peavey VK's, is it of any use?

[CharlieP]

I have a guy asking this question in another forum. My belief is that balanced triodes in the PI slot of a ValveKing is not of any benefit. I came here to ask the experts. Can some of you members that are techs elaborate for me? I have read some high gain amps can benefit from it or hi fi equipment.

[tubeswell]

It works like sonically superior hand-turned wooden control knobs or tone-reflecting paint on the inside of your cab (BTW if he wants, I got some of that paint for sale @ $500 1/2 pint).

[CharlieP]

He claims he read it in a paper online. I read the link and the guy is trying to sell his special balancing above even that of most reputable tube vendors. I say it is snake oil! http://www.guitaramplifierblueprinti...dselection.pdf Page 39 - 42.

[teemuk]

The balancing would only be of use in long-tail pair phase splitters that are also well balanced circuit wise (not too many guitar power amps are).

The PI in Valveking amps is a cathodyne circuit so balancing doesn't help at all since only one half of the dual triode tube is responsible for the phase splitting anyway. Furthermore, these amps have this "texture" control to deliberately unbalance the PI operation because unbalanced operation will introduce even order harmonic distortion, which many people find preferable in guitar amps.

These balanced tubes might have some benefit in some very rare HiFi amps but in guitar amps they have absolutely no use at all.

[Robert M. Martinelli]

Hi all,
I see this "hi-fi blurb" appearing from time to time in "guitar amps" territory, and I fully agree with what you, tw and teemuk said.
Snake oil to the nth power.

Fidelity is something guitar players seldom ( or should I say never ) dig in a guitar amp; it has to be remembered that the various gain stages in a tube amp ( and the PI itself ) are used to shape the sound according to the taste of the designer ( and hopefully, of the "end user" ). As teemuk said, intentionally unbalancing the PI introduces some "asymmetry" in the resulting waveform, which, in turn, puts some emphasis on even harmonics.

Cheers

Bob

[Enzo]

And if you want my view, what all them said.

Balanced PI tubes is kind silly in the first place unless the whole rest of the PI circuit is carefully balanced. What good is a balanced tube if the resistors and caps are all 10%? Furthermore, balancing assumes that high fidelity is the goal, when in a guitar amp clearly it is not.

But teemuk hits the nail on the head. In the Valve King only ONE triode in the tube is used as the PI stage. SO the other side of the tube can;t "balance" with ANYTHING. SO even if balancing has SOME use in paired PI circuits, it wouldn;t in this case anyway.

[CharlieP]

And if you want my view, what all them said.

Balanced PI tubes is kind silly in the first place unless the whole rest of the PI circuit is carefully balanced. What good is a balanced tube if the resistors and caps are all 10%? Furthermore, balancing assumes that high fidelity is the goal, when in a guitar amp clearly it is not.

But teemuk hits the nail on the head. In the Valve King only ONE triode in the tube is used as the PI stage. SO the other side of the tube can;t "balance" with ANYTHING. SO even if balancing has SOME use in paired PI circuits, it wouldn;t in this case anyway.

That is basically what I am trying to get across to him. I told him I had posted this question here for him and I gave him the link to monitor what the professional community here had to say. He would not trust my opinion so if he won't trust the professionals accrued knowledge on the subject that is all I can do for him. I think I will stock up on that tone paint for him too!

[Enzo]

I think the issue of balanced or not is one to leave alone. You can't convince the faithful. But in this circuit only one triode is in use as the PI, so even the hardest core audio tweak ought to understand that the balance idea doesn;t even apply here. They might make the case that a different PI might be "better" but that doesn;t alter that in a single triode PI, balanced is irrelevant.

[CharlieP]

I think the issue of balanced or not is one to leave alone. You can't convince the faithful. But in this circuit only one triode is in use as the PI, so even the hardest core audio tweak ought to understand that the balance idea doesn;t even apply here. They might make the case that a different PI might be "better" but that doesn;t alter that in a single triode PI, balanced is irrelevant.

Yes, but the facts are the facts as only one triode is used! I am trying to show him the facts. He asked the question but didn't want to hear at first. Maybe now he will be able to reason it out.

[MWJB]

Just to reiterate what has already been said in this post...even with a long tail PI (or even a paraphase PI), if you want to introduce an "unbalanced sound" you typically have to start manipulating circuit values...using pretty well any tube with equal spec, but not necessarlily matched triodes (e.g. anything other than a 12DW7 with 2 unequal triodes) will still result in good enough fidelity for 99.9% of musicians (you always have to allow for that 0.1%...if they even exist) to not notice whether there's a matched PI tube or not. Some people even deliberately mismatch the 2 halves of a long tail PI because they like the sound.

If your tube vendor sells "matched triode" PI tubes at a few pennies more than non-matched, then you may as well go ahead, in case you have a customer like the OP's acquaintance, who simply won't be told that it doesn't matter...but don't spend significant amounts & certainly don't expect tonal revelations with a matched triode tube.

I have never come accross an amp with a long tail PI that didn't perform properly with any old, properly functioning, 12A?7 tube in the long tail PI.

The idea that the PI tube is "the most important tube in your amp" is utterly nonsensical. Fixed bias, push pull amps will still run with only one power tube, but they will all stop functioning altogether without any essential tube, whether it be input triode, PI or rectifier.