Back to low gain tubes...

[EtherealWidow]

Had all 12AX7's in again for a while and decided to stop using my compressor pedal. The sound was tolerable. Plugged the compressor pedal and put in two 12AU7's. Forgot how awesome the sound was. Yes, it seems extreme. Yes, the gain is turned all the way up on the crunch channel. But, yes, it sounds awesome. Makes this amp a beast as far as tone goes.

 

[THE TUBENATOR]

In what pre-amp positions are you utilizing those two 12AU7's?

 

[EtherealWidow]

V2 and V3 at first, then switched to V1 and V3. Can't decide what I like better yet. They're both good. Makes the amp a lot less fizzy and farty on high gain settings. For those that don't know, the signal goes to the tubes as follows: V2, V1, V3, parallel to V5 (reverb tube), V4, power tubes.

 

[Krek13]

you forgot to mention the loss of volume

 

[EtherealWidow]

I am indeed sacrificing volume, but getting a much more likeable amp.

 

[Krek13]

I am indeed sacrificing volume, but getting a much more likeable amp.

I don't doubt it, 12at7s 12au7s and 12ay7s soften the tone on any amp, and express really needs softening...I would do the tube change but I really need all available gain...

 

[mcbain]

Hey guys, I'm very interested in doing a tube swap to lower gain tubes, to take some of the edginess or modern sound out of the amp. Are you using Mesa tubes, or another brand? I've never owned a tube amp before my 5:50, and I'm about as technically UNsavvy as one can get. Do I have to take the chassis apart from the combo frame, or can I simply reach up in there and tug the old ones out? Thanks for any advice in advance!

 

[tonefordays]

When I had my 5:25, I used a single lower gain tube - an NOS Philips 5751 in V1. It gave me greater tonal control by taming the amp just enough but without a major volume loss.

 

[gadgetfreak]

So tell me you can throw in the lower gain tubes and there are no repercussions? I understand using a 5751 but the other at7's and so on are different tubes. I thought I read somewhere here a pretty lengthy thread about how the 12at7's and lower gain 12ax7's aren't designed for this amp. Anyone out there know for sure that I won't be damaging my amp by trying, I always get nervous using tubes in an amp that weren't designed for it, I have done so with some of my older fenders but I don't know squat about Mesa Engineering.

 

[thunda1216]

So tell me you can throw in the lower gain tubes and there are no repercussions? I understand using a 5751 but the other at7's and so on are different tubes. I thought I read somewhere here a pretty lengthy thread about how the 12at7's and lower gain 12ax7's aren't designed for this amp. Anyone out there know for sure that I won't be damaging my amp by trying, I always get nervous using tubes in an amp that weren't designed for it, I have done so with some of my older fenders but I don't know squat about Mesa Engineering.

You are not going to hurt the amp. You will just change the gain factor depending on the tube.

 

[EtherealWidow]

I think I remember a thread on here stating that the current tolerance (or some electrical term meaning roughly the same thing) is higher on 12AT7's, but that's about it. They can tolerate it. Doesn't mean that there is actually going to be more current flying around in your amp potentially wreaking havoc on all the inside parts.

 

[gadgetfreak]

Well if you have been using them and have had no issues I have to take that as a good thing and try some out. Thanks for quick responses.

 

[edward]

I think I remember a thread on here stating that the current tolerance (or some electrical term meaning roughly the same thing) is higher on 12AT7's, but that's about it. They can tolerate it. Doesn't mean that there is actually going to be more current flying around in your amp potentially wreaking havoc on all the inside parts.

Yessir. The 12AT7 is diseigned to handle higher current, as in many Fenders' reverb tube position, where the circuit has a higher current draw, necessitating the use of the AT7 tube. The 12AX7, while a higher gain tube, cannot handle the higher current that a circuit designed for an AT7 can. So utilizing an AT7 tube in an AX7 circuit simply results in less gain, but no harm. But you should not use an AX7 tube in a circuit designed for an AT7 as you will tax that tube resulting in a blown AX7 (ahem, at best; at worse can toast a circuit).

Mesa's 12AX7 preamp circuits can be "gained down" with a 5751 (brings down to approx 70% that of an AX7), or to approx 60% with at AT7, or 50% with an AU7. These are very rough estimates as much varies from tube maker to maker, but serves as a general guideline among the tube "families." And when the gain gets changed, not only do the tone and dynamics of the amp change, but everything changes down the line. So the best way to determine what works best really is trial and error, methodically changing one variable at a time, and being objective about differences in tone as well as touch dynamics. Change more than one tube and you don't know what has changed what. FWIW, I've done much of this tube/tone swapping to find "that tone" in my head, and with Boogies (from my Marks of old to my current DC5 and 525), I find the best place to start is with the PI tube. I then go from there. And even when one arrives at a tone that one likes, you can further nuance the tone by trying a different brand tube within the same family. And yes, NOS do make a difference, but "better" is what your ear prefers. So paying more gets you a different tube, but only you can decide whether it's a better sounding tube. Yeah, it can get crazy. But once you arrive at a recipe you like, it is very satisfying!

Edward