Phase Inverter: 12AX7 or 12AT7?

jmv

jmv

New member
Okay guys, curious if anyone here has an opinion on this. Trying to give a little love to my 1966 Bassman, so i just recently bought new powertubes for it, and i'm gonna get new speakers. I also read that you should probably replace the PI tube when the poweramp tubes get replaced.

The tube chart on the bassman calls for a 12AT7 for the PI. Since i've had the amp, its been a 12AX7 in there, for its earlier breakup. Does anyone have suggestions on this tube?? I don't mind the earlier breakup, but i'm curious if there are any other differences in tone, that might be more negative.

Anyone got experience with this??

Thanks,
Jason
 
Re: Phase Inverter: 12AX7 or 12AT7?

It doesn't matter....much. A 12AT7 might give you a little cleaner sound but I don't think it'll be a huge difference. As I understand it the phase inverter feeds the powertubes, it doesn't add gain. My Marshall poweramp calls for a 12AT7 and I replaced it with a 12AX7 and didn't notice a real world difference.......Of course a '66 Bassman might be a little more sensitive to a higher gain tube like the 12AX7........
 
Re: Phase Inverter: 12AX7 or 12AT7?

I happen to thinkit makes a pretty noticable difference...

My advise is this...when you are buying preamp tubes buy one of each and see for yourself.
 
Re: Phase Inverter: 12AX7 or 12AT7?

i may try to buy both, but cash is a little tight since i need to buy speakers for it too.

I'm not really upset with earlier breakup, but i am curious as to how it might affect other aspects of the sound. Does it make a noticeable difference in the sonic character of the amp, or just how easily it begins to distort??
 
Re: Phase Inverter: 12AX7 or 12AT7?

Definately try em out, try it in each position too. You can reinvent an amp quite nicely. I have a couple amps I have done this with. I even have a 12AU7 in a Garnet, made all the difference that I was looking for.
 
Re: Phase Inverter: 12AX7 or 12AT7?

alright. I'm thinking maybe a Tung-Sol 12AX7, and a JAN Phillips 12AT7 blackplate from doug's tubes, whaddaya guys say??
 
Re: Phase Inverter: 12AX7 or 12AT7?

Those Tung-Sol reissues are great and you couldn't buy from a nicer guy than Doug!
 
Re: Phase Inverter: 12AX7 or 12AT7?

jmv said:
Okay guys, curious if anyone here has an opinion on this. Trying to give a little love to my 1966 Bassman, so i just recently bought new powertubes for it, and i'm gonna get new speakers. I also read that you should probably replace the PI tube when the poweramp tubes get replaced.

The tube chart on the bassman calls for a 12AT7 for the PI. Since i've had the amp, its been a 12AX7 in there, for its earlier breakup. Does anyone have suggestions on this tube?? I don't mind the earlier breakup, but i'm curious if there are any other differences in tone, that might be more negative.

Anyone got experience with this??

Thanks,
Jason
Click to expand...

The Marshall JTM-45 and '59 Fender bassman are virtually identical circuits but one big diff is that the Bassman used a 12at7 and the Marshall a 12ax7 for the phase invertor. If you're going for more overdrive go for the 12ax7. Lew
 
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