Replacement of Preamp tubes 12AX7

Makani · #1 09-30-2011, 03:54 PM

I recently read an article in Guitar Player magazine that one can improve (?) the sound from your tube amp by replacing one of the 12AX7 preamp tube with a 5751 tube. I am just wondering if anyone has done this and whether there was much difference in the sound...esp for jazz music. I have a Fender Blues Jr NOS and wanted to try this. Can anyone let me know what you think about this sort of modification?

krusty · #2 09-30-2011, 03:58 PM

Yes, I have tried it, both in my old Mesa 5:25 and my current Mesa Triaxis. It reduces the overall gain of the preamp section, theoretically giving you a bit more clean signal going to the power section. You have to raise the master volume (if your amp has one) to compensate, but if your power section has the ability to compensate without pushing the power tubes into their own distortion, it can work reasonably well.

SamBooka · #3 09-30-2011, 04:13 PM

Yeah.. you just dont hit your power tubes quite so hard with all else (control wise) being equal. Before you try it have tyou tried running your master at 12?

I have a Blues Jr that was pretty hohum until I tried that.. now it is Whoa-hum!

nado64 · #4 10-01-2011, 06:50 AM

I have one in the first level of the amp.
The sound color is more neutral.

The match with the tubes of the others levels is important, too.

Newport · #5 10-01-2011, 10:02 AM

I have found that a NOS GE longplate 12ax7 in v1 is an amazing improvement. I have done it to all of my blackface fenders and it has never gone un noticed. I would look online for one. Should be a fairly inexpensive upgrade.

bborzell · #6 10-01-2011, 10:43 AM

My tube amp tech mentioned last night that the most significant improvement for a Princeton comes with replacing the 12AX7 in the preamp socket with an RCA 12AX7.

They are not easy to come by, but he finds them every so often. Probably the cheapest way to get noticeable sound improvement. I am on the lookout.

Allenl · #7 10-17-2011, 07:09 PM

Quote:

Originally Posted by Makani

I recently read an article in Guitar Player magazine that one can improve (?) the sound from your tube amp by replacing one of the 12AX7 preamp tube with a 5751 tube. I am just wondering if anyone has done this and whether there was much difference in the sound...esp for jazz music. I have a Fender Blues Jr NOS and wanted to try this. Can anyone let me know what you think about this sort of modification?

If you're playing clean, it doesn't make that much difference. If you want to smooth out your OD to hear more of your guitar's wood in your tone, on those on the verge of breakup type situations, then replacing the v1 12AX7 with a 5751 or 12AT7 will make a significant difference, in achieving this end.

medblues · #8 10-18-2011, 09:05 AM

According to BillM, who is an expert on everything Blues Jr, tube changes in that amp do not amount to any more than a little turn of your tone or volume knobs. Bias adustment, however, makes a bigger change in your tone. He has written that Blues Jrs leave the factory biased too hot (favoring rock and blues).

Quote:

Originally Posted by Makani

I recently read an article in Guitar Player magazine that one can improve (?) the sound from your tube amp by replacing one of the 12AX7 preamp tube with a 5751 tube. I am just wondering if anyone has done this and whether there was much difference in the sound...esp for jazz music. I have a Fender Blues Jr NOS and wanted to try this. Can anyone let me know what you think about this sort of modification?

SamBooka · #9 10-18-2011, 10:13 AM

Yeah.. I have discussed this several times with Bill. The thing is if you run your tubes at 100% Static Dissipation it will sound VERY similar to running them at 75% Max Static Dissipation. The difference is more along the lines of how long the tubes last. You will notice more of a difference running them below 70% where they will be biased more coldly

Makani · #10 10-18-2011, 05:54 PM

After changing the v1 preamp tube to a 5751 I also turned the Master Volume to 12....the result when playing was a very clean articulation of notes on my guitar (D'Aquisto Jazzline)....the bass strings were abit "muddy" before but now there is no muddiness...high notes ring clearer...it may be my imagination but the sound changed when I switched the 5751 to the v3 position...not as noticeable a difference maybe slightly clearer than with the 12AX7.

jmstritt · #11 10-18-2011, 05:59 PM

You might want to also try a higher headroom set of power tubes. If you go to a good place like Groove Tubes, thetubestore.com, etc you can tell them, "Hey I play Jazz, send me some EL 84s that won't distort too early!" And they can accomidate you. That will make a big difference in conjunction with the 5751.

SamBooka · #12 10-18-2011, 06:01 PM

just curious.. what 5751s are we using?

hallpass · #13 10-18-2011, 08:24 PM

I have a 5751 in the v1 of both my PRRI and 71' Bandmaster combo. I'm happy with how it sounds/feels and feel like along with an efficient/sensitive speaker, can help improve clean headroom some.