Lower gain tube in PI position

[BSS]

I've read of some guys throwing a 12at7 tube in the phase inverter position. What affects does this have on the amp's sound?

 

[mysticaxe]

I did this once in a TSL and didn't like it much. You could turn the amp up a little more for the same volume level, but I thought it made the sound quite a bit "boxier." I ended up putting a 12ax7 back in and thought I got much better tone. That's 1 experience with 1 12at7 in 1 amp. What is that worth?

 

[Buckeyedog]

The lowest I'd go is likely a 5751. The AT7's I've tried and didn't care for too much. But do like the 5751 in many amps. Especially great in a Marshall DSL. Just smoothed it out a bit.

 

[MOAAH]

IMO the 5751 is the tube to try in a 12ax7 PI, if you're not happy. 12at7 works fine in amps designed for it, but in 12ax7 amps I found it rather flat and somewhat hollow, or as someone said above, boxier.
That said it can't hurt anything, so try it cause tone is subjective.

 

[Nigel]

Stick a long plate, like a Sovtek LPS or if you can spare the $$ a real old stock Mullard long plate.

 

[Tawlks]

I'm interested in this too.... Was thinking of trying a 12AT7. Not famillier with the 5751 myself.

 

[johnnyjellybean]

Stick a long plate, like a Sovtek LPS or if you can spare the $$ a real old stock Mullard long plate.

+1 !! Sovet LPS or Ei longplate and if you have the extra coin, a longplate Telefunkfen

 

[~Abstract~]

Stick a long plate, like a Sovtek LPS or if you can spare the $$ a real old stock Mullard long plate.

wouldn't a real mullard do more for the amp in v1?

 

[just42dave]

Stick a long plate, like a Sovtek LPS or if you can spare the $$ a real old stock Mullard long plate.

wouldn't a real mullard do more for the amp in v1?

teh real mullardz are good anywhere....

 

[MOAAH]

Stick a long plate, like a Sovtek LPS or if you can spare the $$ a real old stock Mullard long plate.

wouldn't a real mullard do more for the amp in v1?

Yes it would, simply cause V1 is the beginning of the circuit so it's tone would be amplified throughout the rest of the amp.

IMO going by over 40 years of tube amp use, repairs and builds, I find Mullards to go micro-phonic way easier than say Telefunken or any one of these American NOS:

Oh and there's a 5751 on the far right, good luck finding any cheaper than ~50USD.

 

[FuelGTRX]

I tired a couple of low gain tubes in the PI socket in my old Splawn QR, Laney GH50L, and Soldano HR50+. I tried a NOS RCA 12AT7 and a JJ ECC81. In the Splawn, I found it warmed and fattened the amp up a bit more and gave a hair more sag. It sounded pretty good, so I kept it there. It made the Laney sound less dry and added some sag as well. In the Soldano, I didn't like it so much. It warmed up and thickened the sound too much. Made the amp a bit mushy is response. The RCA had more of an effect than the JJ in both amps, but both did the same thing.

Now, these were just subtle changes. It wasn't imaginary as you could easily tell the difference between these tubes and 12AX7 tubes, but it was only a bit more noticeable of a change than switching preamp tube brands. But judging by how differently it acted with these 3 amps, it may be more noticeable in some circuits than in others.

 

[vchizzle]

I've found this Mullard 12at7/cv4024 sounds great in V1 on my amps, haven't tried in PI though:
http://www.dougstubes.com/12at7.html
2nd tube from top of page.

 

[Nigel]

That CV4024 is the gateway mullard...

...and yes they sound great in V1. That's why I have one in V1, V2, and the PI of my Mofo.

 

[fek]

In my Randall RM's, dropping a 5751 into the PI added some clarity and more usable range to the gain knobs.

 

[FastRedPonyCar]

I've tried an AT7 in all of my amps PI and didn't really dig it at all. sort of neutered them... especially the nitro. It killed all the impact and whallop that the sound has when it hits you. 5751's aren't as bad but it still sounds like it's sucking some life out of it and not improving the tone. They're all NOS mullard AT7's and GE 5751's too.

 

[luxxtone]

I used a 5751 in the PI slot on a Soldano Avenger to control the amount of usuable gain. Sounded great IMO. Cleaned up a little of the fizziness and sounded tighter and more grindy, as opposed to more fuzzy. I think a 12at7 might bring it down too much like others have mentioned. Try it out...it's easy and cheap!

 

[RockStarNick]

People often forget that even though a 12AT7 has the same pins as a 12AX7, and they're technically interchangeable, it's a totally different tube design. It's more of a utility-function tube, not a great tone-producing tube. I've always found AT7s hollow, harsh, and kinda sterile.

Whereas a 5751 is identical to a 12AX7, just with less gain.

In my experience, a lower-gain tube in the PI will soften things, and perhaps give the perception of fattening them because the highs are softer.

 

[BSS]

I used a 5751 in the PI slot on a Soldano Avenger to control the amount of usuable gain. Sounded great IMO. Cleaned up a little of the fizziness and sounded tighter and more grindy, as opposed to more fuzzy. I think a 12at7 might bring it down too much like others have mentioned. Try it out...it's easy and cheap!

This is exactly what I'm looking to do with my Jet City (Soldano Atomic 16).

Thanks for the replies guys, definitely some good info.

 

[Nigel]

People often forget that even though a 12AT7 has the same pins as a 12AX7, and they're technically interchangeable, it's a totally different tube design. It's more of a utility-function tube, not a great tone-producing tube. I've always found AT7s hollow, harsh, and kinda sterile.

The Mullard 12AT7 is an exception. That tube is tone-town for under $30 NOS.

 

[ericsabbath]

rft ecc82
they go for like 1/3 the cost of the ecc83 ones on ebay