12AY7 PI tube, good, bad or ugly? Your thoughts please.

[sjturbo]

Morning! I have put a 12AY7 in my Carvin Belair (VT50) style amp. EL84's ect. I seem to be getting a bit more compression in the sound which also seems to add some touch sensitivity to my picking? Can those in the tube community voice their thoughts on the use of a 12AY7's in the PI position? I know it has less gain and higher current to the power tubes but I would appreciate your inputs. Thanks!

[Leo_Gnardo]

12AY7 is sort of an in between tube, less gain than AX and more than AT. However it does not deliver "more current to the power tubes." If you like the way it works in your amp I don't see any reason not to use it.

[Justin Thomas]

Hey SJTurbo & Leo,

12AY7 has an amplification factor of 44, so less than both AX & AT. I have a couple I got out of a projector, and they're really nice tubes. But of all the various 12A_7 subs, the AY is THE most direct sub that needs no circuit mods to run "ideally." The AT7, AU7, AV7, all should have circuit tweaks to run at "optimum," but usually in a guitar amp, we just don't care. But putting in an AY in place of an AX, rather than an AT or AU, definitely keeps the high end intact and cuts the gain, although the volume difference is negligible.

I've only used them in an actual preamp stage, usually first and second. I like these tubes, and remember - the 12AY7 is the AUTHENTIC tweed sound. I'm surprised they haven't caught on more, unless it's possible to just use an AX7 at a lower margin through circuit tweaks. I think compared to AX7s, AY7s are pretty pricey, even for new production.

Not trying to throw down the correction hammer, just that I memorized the factors for all kinds of "oddball" tubes so I could keep a lookout for "potential usefuls" when I'm out thrifting.

Justin

[mozz]

12AY7 is the AUTHENTIC tweed sound, when used in V1. I would try a 12at7 at the PI or a 12AU7. I think it would be more common, maybe for a reason. If you have a original 12ay7, i would save it or use in V1, you can pick up a nice original 12at7 cheap compared to others.

[tubeswell]

What moss said. 12AY7 in V1 sounds kinda bluesy, but a 12AT7 in the LTP position makes the amp sound fat.

[mozz]

I like pushing the 12at7 for PI use. I use it whenever i build. Even if i repair a amp for a customer, i often try a 12at7 and will tell them that up front so they can swap back if they want. ( i have a few hundred). If the current tube is a 12ax7, which i think it is, according to the schematic it has 100k plate resistors, try the 12at7 there, if you don't like it you can easily tack solder another 100k on top to drop it to ~47k and see if you like it there. Easy enough to undo.

[sjturbo]

Interesting inputs. So why an AT over a AY in the PI position? And please explain the need to change the plate resistors for the AT or AY in the PI position?

[pdf64]

Firstly it would be a good idea to check that the LTP plate resistors aren't having their dissipation rating pushed when subbing, as different tube types draw different currents.

You don't 'need' to change the values, however if you believe in the concept of circuits being designed, the existing values may have been selected to optimise the conditions for the stock tube type. If a different tube type is just bunged in there, it may not sit at a suitable operating point.

An LTP such as used here can't supply any appreciable current to the power tube grids, no matter what tube you sub in there.

To do that, a special driver circuit is required, which will use a transformer or direct coupled buffers.

Yes, I'm afraid you may have read some nonsense to the contrary on various 'tone guru' websites, written by someone that doesn't have a good grasp of the basics, which has then been copy/pasted into the innumerable 'tone guru' sites.

[sjturbo]

Nice sounding sound/video clips pdf64! Not being a EE I sometimes look to "tone guru's for opinions. But I am aware that not everything you read on the Net is true or factual! I do try to verify information by searching out more than one source. That being said I do look at my schematics, comparing to others and try to understand the whys. I did look at The Valve Wizard -Long Tail Pair to help understand your point regarding the plate resistors and understand it somewhat. But I do try to weed out the tone gurus that have no electronic or practical knowledge of circuits. Thanks for the inputs.

[Enzo]

Opinions are neither right nor wrong, they are opinions. Your tone guru can have an opinion, and it is as valid as anyone else's. Tech oriented people can talk of impedance, load lines, etc etc, but that doesn;t make their opinions more or less valid. They explain how a circuit works, but not how it will sound to your ear. You can do some mods out of a Gerald Weber book, and have not the slightest idea what it did to the circuit, but you will like the change or you won't.

Evaluating opinions is tough. You might assure me that clam chowder New York style is way better than New England style. What does that mean to me? Nothing. First I hate the taste of clams any way you make them, but NY style is tomato based, while NE style is cream based. You prefer the tomato style, and I prefer cream style. No one is wrong.

Changes to circuits that promise more upper midrange at least describes the result. But promise me "100% improvement", and that means exactly zero.

[sjturbo]

Opinions are just that. I'm not so into "alternative facts". What sounds good is subjective. Design principles are important guidelines when building an amp. When modifying an amp it is likely beneficial to understand them as not to cause problems that may cause damage. I ask for opinions from both those who have "experimented" and from those who have knowledge of electronics and appreciate both!
BTW I'm a NE Chowder man! Tomato sauce is good on spaghetti.