Marshall JCM 800 preamp tube question... Phase inverter.

[Fret-Shredder]

Hey guys. Concerning my 1983 JCM 800 2204. I understand that V1 and V2 have the most effect on the the gain for the preamp but my question concerns V3 the phase inverter. How important is that tube? Is there a recommended 12AX7 for that position. Thanks in advance.

 

[Marshall Freak]

I usually run a Chinese preamp tube. Some tubes can make a difference in v3, but not all that much.

 

[Racerxrated]

I really like a Tungsram 12ax7 in there...I think Psychodave mentioned that in a long ago post and I had one around, threw it in an instant improvement. Seemed more 'ballsy'. I've also heard Ei pre war 12ax7s work well. You could try an old NOS or strong 12at7 as well, some say it improves clarity.

 

[glpg80]

Electronically you want a well balanced triode with long plates for better phase match and linearity. This will help cancel common mode noise and distortion going into the power tubes.

 

[Fret-Shredder]

Electronically you want a well balanced triode with long plates for better phase match and linearity. This will help cancel common mode noise and distortion going into the power tubes.

I'd appreciate any recommendations you might have.

 

[psychodave]

Electronically you want a well balanced triode with long plates for better phase match and linearity. This will help cancel common mode noise and distortion going into the power tubes.

I'd appreciate any recommendations you might have.

Ei’s. I changed over thanks to a tip from Larry.

 

[glpg80]

Electronically you want a well balanced triode with long plates for better phase match and linearity. This will help cancel common mode noise and distortion going into the power tubes.

I'd appreciate any recommendations you might have.

I’m a big fan of JAN tubes which stands for joint air force navy as they are milspec quality. If you can, find a plate that’s physically long in the glass envelope and has a fairly hi mu. 12AU7 may be too low of a mu for guitar amplifiers but were made for phase inverter stages.

 

[Fret-Shredder]

Electronically you want a well balanced triode with long plates for better phase match and linearity. This will help cancel common mode noise and distortion going into the power tubes.

I'd appreciate any recommendations you might have.

I’m a big fan of JAN tubes which stands for joint air force navy as they are milspec quality. If you can, find a plate that’s physically long in the glass envelope and has a fairly hi mu. 12AU7 may be too low of a mu for guitar amplifiers but were made for phase inverter stages.

Would you recommend any these...

 

[psychodave]

Based on the description and knowing tubes they are short plates. I have a bunch of those tubes and they sound good.

 

[Fret-Shredder]

Based on the description and knowing tubes they are short plates. I have a bunch of those tubes and they sound good.

Any particular one you recommend for the phase inverter position.

 

[CEG85]

From personal experience, V1 makes the biggest impact on sound.
I've gone through a bunch of PI tubes from W. German telefunkens to JJ's and tonal impact has been negligible.

However if you are planning to experiment, I would consider using tubes with balanced triodes, preferably long plates.

For what it's worth, I've strictly used either JJ or sovtek 12AX7 LPS in all my amps without any problems.

 

[Kordoba]

I use Sovtek LPS in the phase inverter in all of my amps. It makes the most difference in my VTM and Crate Stealth. There's also a JJ long plate that I like, but can't remember which one it is.

 

[SpiderWars]

IME in a MV amp the PI tube makes less of a difference. And it will be more of a subtle EQ change rather than changing the character of the distortion if that makes sense.

The new Mullards are good here too, they look pretty much identical to Sovtek LPS construction-wise.

 

[napalmdeath]

I use Sovtek LPS in the phase inverter in all of my amps. It makes the most difference in my VTM and Crate Stealth. There's also a JJ long plate that I like, but can't remember which one it is.

Me too. I wouldn't waste money on an NOS tube for the PI. A balanced Sovtek 12AX7LPS is my go-to. Save the fancy tubes for V1, where they have the most impact on your tone.

The JJ mentioned above is the 803S.

 

[itsme]

I use Sovtek LPS in the phase inverter in all of my amps. It makes the most difference in my VTM and Crate Stealth. There's also a JJ long plate that I like, but can't remember which one it is.

Me too. I wouldn't waste money on an NOS tube for the PI. A balanced Sovtek 12AX7LPS is my go-to. Save the fancy tubes for V1, where they have the most impact on your tone.

The JJ mentioned above is the 803S.

Me also. Sovtek LPS in all

 

[stratjacket]

I use Sovtek LPS in the phase inverter in all of my amps. It makes the most difference in my VTM and Crate Stealth. There's also a JJ long plate that I like, but can't remember which one it is.

Me too. I wouldn't waste money on an NOS tube for the PI. A balanced Sovtek 12AX7LPS is my go-to. Save the fancy tubes for V1, where they have the most impact on your tone.

The JJ mentioned above is the 803S.

Me also. Sovtek LPS in all

Another one here, I use the sovtek 12AX7 LPS in all my amps as the PI tube including a 1984 JCM 800 2205. Works great.

 

[fek]

I always thought the LPS is kind of the go to. If I am looking for more clarity a 5751 does a good job for that in the PI.

 

[Fret-Shredder]

I'll grab a Sovtek LPS and give it a try. Thanks guys for the advice.

 

[RedPlated]

I use LPS in a lot of my amps. It does add bass though. Every amp
I’ve put them in. It’s like turning the bass knob up 2 steps. Not flubby at all, but you’ll notice it.

Can’t remember what I have in my 800. Some amps I use a JJ ECC803 long plate. Just depends.

 

[Fret-Shredder]

I ordered a pair of the Sovtek 12AX7LPS. One for my 1983 JCM800 2204 and one for my 1977 JMP 2203 Master model. Thanks again for the help.