Regular 12AX7 in place of a phase inverter?

[emperor_black]

First off, apologies if this has been asked before. I'm having too much fun replacing the JJ preamp tubes that came with my Mark IV with Sovtek's. The R2 channel is much more usable. The JJ's seemed to suck all the gain out of the channels. Anyway, the last tube left is the phase inverter. I would like to replace that too with a Sovtek (because that's all I have for now ). Can I replace the phase inverter tube with any 12AX7? I know when I ordered phase inverters for my carvin, I had to specify so. But what really is the difference between a regular 12AX7 and a phase inverter tube?

And the 12AT7 in the V4 position, what channels does it affect? Can I put a 12AX7 in its place? Is it safe? Thanks much for your help!

Sam

 

[MrMarkIII]

The phase inverter can be thought of as a gateway or interface between the pre-amp and the power section. Any 12AX7 or variations thereof can be used. Unlike the gain-producing tubes in the pre-amp, none of the amp's controls really affect the phase inverter. Some like a "balanced" tube for this position (there are two sections to these tubes), but this is a left-over from tube hi-fi days, and it's doubtful you would notice any audible difference. In any case, the so-called balance disappears as you play, just as impedance and damping and other factors change while actually using the equipment.
It sounds like you have an early Mark IV, and the 12AT7 is the Reverb tube. You should leave that alone. It's usually OK to replace a high gain (12AX7) with a lower gain tube (12AT7), but going the other way in a reverb circuit will probably result in excess noise and a degraded sound.
Somewhere on this forum you should be able to find a copy of the Mark IV-A manual.

 

[emperor_black]

thank you mrmarkIII. I replaced all but the phase inverter tube with Sovtek's. Now the Mark IV has a growl and plenty of bite and crispness. Anyone complaining the mkiv sounds too "smooth" should look at replacing the preamp tubes.

 

[thunda1216]

I too really dislike the JJ preamp tubes. I feel that they have been over hyped. They seem dull and lifeless to me. The Sovtek 12AX7WC is a really nice sounding short plate tube and I *really* like the Sovtek 12AX7LPS as the phase inverter in most *any* amp - makes me smile.

ty

 

[droptrd]

I to really dislike the JJ preamp tubes. I feel that they have been over hyped. They seem dull and lifeless to me. The Sovtek 12AX7WC is a really nice sounding short plate tube and I *really* like the Sovtek 12AX7LPS as the phase inverter in most *any* amp - makes me smile.

ty

Im a big fan of both the WC and the LPS. I really love the LPS in all positions of a recto. Never liked the JJs until I picked up my stiletto. Its now my tube of choice for V2 and V3 of my stiletto. Helps tame the harsh highs.

For the PI postion, I just use a regular LPS in EVERY amp. I used to do the balanced LPS's, but I honestly cant tell the difference between the two.