12AU7 vs. 12AX7

[guvna2030]

I read an article over the weekend about the different types of interchangeable tubes that you can use instead of 12AX7's. It stated that the 12AU7's have less gain than the 12AX7. Anyone have any experience using them or have any advice on using these preamp tubes instead of the typical 12AX7's? I'm looking to soften the gain on my DC-3 a bit.

Thanks!

 

[jackieTHEjokeman]

Go to Eurotubes.com and email Bob. He will explain what they are and suggest what you need to do. He'll explain it better than anyone here.

 

[Russ]

You should try a 5751 or a 12at7 first before sliding all the way down to a 12au7. The gain of a 12au7 is really weak. Probably too weak for realistic use in a guitar amp. I have had success with 12at7s in my other amps. I haven't tried one in the MarkIV except in the designed reverb driver position. The 12at7 made my Marshall a totally different animal. I couldn't believe it. I never heard a Marshall so clean. I thought I was hearing a Fender.

 

[harryjmic]

I may be off a little on the gain factor which is for every volt in you get X amount of gain, this being said this is what I remember from some Gerald Weber articles in the Vintage Guitar magazines.

12ax7 = 100
5751 = 70
12at7 = 60
12ay7 = 44
12au7D = 20
12au7 = 17

12au7's really kill amps, as far as anything really good happening by using them. One tube to look at is the 12dw7, half 12ax7 and half 12au7. Every twin triode is esentially two tubes in one. Personally, I don't care for 5751's and I have about 5 of them that never make into any amps I have.

 

[hans-jürgen]

If you don't want to lower the gain that much, you could also try out a RCA 7025 if you find one (or a similar new production tube). I compared it to an old Valvo ECC83 (grey long plates, made by EI) the other day in V1 of my Mark IIB and was surprised how big the difference in gain was, comparable to PAF vs. high output pickups. The Valvo sounded more "modern" towards high gain amps while the RCA really offered that vintage sound with a lot of dynamics and warmth with harmonic distortion.

 

[Russ]

You might also try not turning your gain so far to the right... You can try just using less gain on the knob. Looking for a less gainy sound often requires more reserved use of the knob. You might also try lower output pickups or changing your speaker type. Sometimes just running your tone knobs down a little can help too on your amp and your guitar in addition to the guitar's volume knob.

 

[RR]

Everything Russ said from trying a 5751 or 12AT7 to laying off the gain, changing pickups etc ... :wink:

i just changed the V1 tube of my Studio .22+ from the 12AX7 to 5751. It helped smoothing out the drive. You do lose some of the "metallic edge" (expected) but it return you have a smoother warmer distortion, that's the obvious trade-off.

I may go even further down to 12AT7 because the gain of the drive channel is "only" on "3". Still too much gain for my liking.

 

[guvna2030]

Thanks for the responses. Perhaps I can be a little more specific with my question and you guys can help me out:

I am currently in a band that plays "folk rock". Basically, there is an acoustic guitarist/singer, an electric lead (that's me), drummer, and a bassist. For rhythm work, I'm looking for an overdriven sound without too much distortion (high gain muddies the sound too much, even at 2 or 3 with the 12ax7). I have a TS-808 that I'm using for my leads but it's not quite the right sound for articulating chords over the acoustic. The comment above about the warmth of a 12at7 may be just what I'm looking for. Any other suggestions for getting a full, sustained, slightly distorted sound that won't overpower or otherwise ruin the folk-ish feel of a song? I'm not sure that I want to completely eliminate the possibility for high gain because I am in another project where heavy distortion is just what the doctor ordered.

Btw, I mostly use an SRV strat that's been modified with 50s and 60s pickups and a fatter neck, along with an Eric Clapton strat with gold lace pickups.

 

[Russ]

The reason I know that the 12at7 works is because I had one in my JMP for a while. I had it in V1. Same purpose different amp. The gain was different, much less but smoother drive. Then I tried one as V3 (PI). This made the power section smooth out too and not drive as hard. You might try it in your PI position also. I remember some guys going for both. In the JMP it was like playing a tame Fender with just the hint of that growl but it was more like a warm feeling. Many people are obsessed with achieving gain and not tone. Distortion is great for some things but in the context like your band playing folk is out of place. Some styles of music need real tone. It is in there, the circuit is designed to make gain. Cut it where it makes it and you get tone. 12at7s are great for that. In fact, in my MarkIVa I have a 12at7 as a reveb tube. I have thought about swapping the reverb and the V1 when I feel like making that smooth tone. I would just sacrifice the reverb. The swap is nothing new and is all over the place if you look. I don't think that the 12au7 would even have enough gain to make enough sound to play with a band though. You gotta have some signal.

 

[Russ]

I would try going to a blue lace in the neck instead of gold. I had some nice blues coming out of my old strat. Maybe try a silver in the middle too. For the SRV play neck and middle. I think that would get a good folk sound if you aren't using the Texas pups. The 50's and 60's pups will sound good in that position. Keep your volume rolled off too. Too much signal from your pups can cause unwanted gain. Also for that fat tone keep your tone down too. Dimed tone makes for too trebly a tone for folk. You really want a clean warm natural vibe. Then to punch out front roll your volume up on your guitar a tad, but leave your tone alone. This will give you a little boost. Many people overlook their guitar knobs as controls. I have often told people that if their knobs were meant to be dimed all the time they wouldn't be there. A potentiometer is used to dial in and out, it allows for more than one sound. You could also try a darker sounding tube like a JJ, that might help some too but won't be like running a 12at7.