• TalkBass has been independent since 1998. Add your voice.
    Create a free account to reply to discussions, view embedded media, and browse with fewer display ads.
    Join free Log in
    Want zero display ads or expanded classifieds tools? Compare plans.

6SL7 vs 12AX7

#2
Everyone will tell you 6SL7, but I've spent a lot of time working with both, and the circuit design matters more than anything. So it depends on the context in which it's being used - a good 12ax7 design can stomp a mediocre 6SL7 design. I've also built pretty much identical circuits with both, and compared them side by side (there's a video on my YT page), and they are a lot closer than you might think. Each has attributes that folks might prefer over the other depending on tastes. Right now I'm loving the 12au7, so go figure.
 
Last edited:
  • Like
Reactions: tombowlus, nashvillebill and jeff ward
#4
Ya, my B-15N has 6SL7's and I love it, yet my SVT and V4B have 12ax7's and I love them, too. So it's very much the circuit as JGR says.

However, a complicating factor in all this, too, is in a B-15, new 6SL7's sound not as ballsy and a little on the meh side compared to old ones, and I only use NOS in my B-15N for that reason, and I'm sure that's why the Heritage B-15 came with NOS 6SL7's. Notice that when they made an less expensive Heritage B-15N, they went with 12ax7's...wouldn't really have cost them more to make them with 6SL7's, but new 12ax7's are much better than new 6SL7's so that had to enter into the decision. But JGR's preamp that has 6SL7's sounds terrific and so does the Jule Monique, and both of them have new 6SL7's, so the circuit can't be denied.

Would they sound much better with NOS 6SL7's? I don't know. Maybe JGR or Jule or their customers can shed some light on it. But if I were in the preamp making business, I'd probably use 12ax7's just because new ones are quite good these days and they're everywhere.
 
#5
JimmyM said:
Ya, my B-15N has 6SL7's and I love it, yet my SVT and V4B have 12ax7's and I love them, too. So it's very much the circuit as JGR says.

However, a complicating factor in all this, too, is in a B-15, new 6SL7's sound not as ballsy and a little on the meh side compared to old ones, and I only use NOS in my B-15N for that reason, and I'm sure that's why the Heritage B-15 came with NOS 6SL7's. Notice that when they made an less expensive Heritage B-15N, they went with 12ax7's...wouldn't really have cost them more to make them with 6SL7's, but new 12ax7's are much better than new 6SL7's so that had to enter into the decision. But JGR's preamp that has 6SL7's sounds terrific and so does the Jule Monique, and both of them have new 6SL7's, so the circuit can't be denied.

Would they sound much better with NOS 6SL7's? I don't know. Maybe JGR or Jule or their customers can shed some light on it. But if I were in the preamp making business, I'd probably use 12ax7's just because new ones are quite good these days and they're everywhere.
Click to expand...


I too find the new 6sl7s kind of blah so I always use NOS - mostly RCA.
 
#7
JimmyM said:
Ya, my B-15N has 6SL7's and I love it, yet my SVT and V4B have 12ax7's and I love them, too. So it's very much the circuit as JGR says.

However, a complicating factor in all this, too, is in a B-15, new 6SL7's sound not as ballsy and a little on the meh side compared to old ones, and I only use NOS in my B-15N for that reason, and I'm sure that's why the Heritage B-15 came with NOS 6SL7's. Notice that when they made an less expensive Heritage B-15N, they went with 12ax7's...wouldn't really have cost them more to make them with 6SL7's, but new 12ax7's are much better than new 6SL7's so that had to enter into the decision. But JGR's preamp that has 6SL7's sounds terrific and so does the Jule Monique, and both of them have new 6SL7's, so the circuit can't be denied.

Would they sound much better with NOS 6SL7's? I don't know. Maybe JGR or Jule or their customers can shed some light on it. But if I were in the preamp making business, I'd probably use 12ax7's just because new ones are quite good these days and they're everywhere.
Click to expand...

I haven't messed around too much with the new 6SL7's. The old ones are not really terribly expensive by comparison, and I tend to maximize my 'bang for the buck' by concentrating on the V1 position and letting the tube that drives the tone controls be a lesser concern. The Shuguang tubes that came in my Monique sounded fine, but I had a problem with the V1 tube where it had some kind of intermittent failure that took a few trips across the country to get sorted out. Since even early on, I was elbow deep in the unit, I didn't have any qualms about trying some stuff out along the way.

If you like mid-forward or mid punch in a tube, you should check out 'old stock' Tung Sols. I had a couple, the first of which (a gift from another TB'er) showed slightly more gain than other types of 6SL7, and had more mid going on (this was sort of confirmed by yet another TB-tube designer, who said I'd probably like the TS for its extra 'ooomph'). Unfortunately it was also microphonic. I did run a NOS/JAN RCA blackplate that didn't have that mid character or extra kick, but DID have a really nice deep extended bass range.

Now I'm back with an old Tung Sol, and I really like it. Didn't cost an arm and a leg and it has some mojo to the mids that I don't hear in some of the others I've tried.
 
#8
I find that my amps with (I only use NOS) 6SL7's are harmonically richer.

On a large scale, producing an amp using tubes from the 12A?7 family is more cost efficient so manufacturers tend to go that way.

What tube works best depends on the application and the design as has been mentioned.
 
#9
I got a couple converter sockets off ebay that let u plug a 6SL7 into a 12AX7 slot. I tried them out on my ALLEN and noticed they are a little cleaner and have a bit less volume than the old 12ax7 that the amp had in it.

The tones are both great I recorded a video so ill post it here in a bit.
 
#11
jeff ward said:
I got a couple converter sockets off ebay that let u plug a 6SL7 into a 12AX7 slot. I tried them out on my ALLEN and noticed they are a little cleaner and have a bit less volume than the old 12ax7 that the amp had in it.

The tones are both great I recorded a video so ill post it here in a bit.
Click to expand...

Unfortunately, live isn't that simple that you can simply swap the tubes. Doing that will make a tonal difference and it depends on how hard you push your amp.

The design of the tube in the circuit matters, how the tube is biased, what plate voltage is used, the signal level that is fed into the tube, how the power supply reacts to the demand that the tube makes, etc. The tube will perform differently if the amp is pushing it into more nonlinear operating regions. For such a simple device, how it performs is complicated.
 
Last edited:
#13
jeff ward said:
For all u tone freaks out there, which do u like best for your bass tone and why?
Click to expand...

6SN7, 12AU7, OPA2132, LT1124.

Why? Because I swing towards clean and low gain. Link Removed

OTOH, as JGR says, it's all about design intent and acumen. I've built decent sounding bass preamp sections using both 6SL7 and 12AX7 and in many cases could find the same results using either one, I think. For me one big attraction to 6SL7 is the ready availability of nice NOS ones at reasonable prices.
 
Last edited:
  • Like
Reactions: BurningSkies
#15
I'd pick a 6sl7 over a 12ax7, under the condition that I had access to a supply of good quality NOS 6sl7 tubes. If I could only use new tubes in it, I would go 12ax7. If given the choice of using any octal NOS tube, I would pick 6SN7 over 6SL7. Favorite tubes of any era are small signal pentodes like 6au6, crazy gain in a single stage with pretty good tone, but the circuit has to be designed carefully or they sound like crap.

The thing I like about the 6SN7 is that it is actually beefy enough (and have the right load resistance) to use as a low power output stage in a mini amp. Set it up for push pull output stage and you can get a little less than 1 watt out of it, fender reverb transformers match up to it pretty well, fun for DIY.
 
#16
Well the only experience I have of 6sl7's is in an old Elpico 5watt amp in combination with 6v6 and glass rectifier circuit just like the old fender champ C1, so I don't know what the tonal differences are on that one tube as the champ f1 had a 12ax7 and an EL84.
As it's used in the Elpico it has a lot more progressive break up than the 12ax7's in my Ampeg or Mesa tube pre amps.
I can't think of an instance where you could hear that one tube change apart from the adaptor socket, but as someone has mentioned the circuit around the tube probably. Contributes a lot.:)
 
Last edited:
#17
Bassmec said:
Well the only experience I have of 6sl7's is in an old Elpico 5watt amp in combination with 6v6 and glass rectifier circuit just like the old fender champ C1, so I don't know what the tonal differences are on that one tube as the champ f1 had a 12ax7 and an EL84.
As it's used in the Elpico it has a lot more progressive break up than the 12ax7's in my Ampeg or Mesa tube pre amps.
I can't think of an instance where you could hear that one tube change apart from the adaptor socket, but as someone has mentioned the circuit around the tube probably. Contributes a lot.:)
Click to expand...

Well the ALLEN was designed for 12ax7 as u can see it stamped on the back of the amp in my video. I'm sure if it was designed to use 6sl7s it probibly woukdnt sound much different from its 12ax7 design since the maker was obviously going for a specific Tone with this amp.

My video was just showing how the 6sl7s changed the tone of my allen when I replaced the 12ax7s using the 6sl7s and the tube converter socket.
Just incase anyone else wanted to buy a set and try it with there amps that use 12ax7s.
Its a cool and simple way to get some different tones from your amp, and sure the results may be different with different amp designs but at least this way u can play around with your sounds without building a new amp from the ground up just to try some 6sl7s.

In my video the tone is clearly different once I pull the 6sl7s and put the 12ax7s back in.
With those converter sockets is a cool way to play around with different tones.
 
#18
jeff ward said:
Well the ALLEN was designed for 12ax7 as u can see it stamped on the back of the amp in my video. I'm sure if it was designed to use 6sl7s it probably wouldn't sound much different from its 12ax7 design since the maker was obviously going for a specific Tone with this amp.

My video was just showing how the 6sl7s changed the tone of my allen when I replaced the 12ax7s using the 6sl7s and the tube converter socket.
Just in case anyone else wanted to buy a set and try it with there amps that use 12ax7s.
Its a cool and simple way to get some different tones from your amp, and sure the results may be different with different amp designs but at least this way u can play around with your sounds without building a new amp from the ground up just to try some 6sl7s.

In my video the tone is clearly different once I pull the 6sl7s and put the 12ax7s back in.
With those converter sockets is a cool way to play around with different tones.
Click to expand...

You could also just try using a 5751 instead of a 6SL7, the gain factors are very close and no adapter is needed

Building new amps from the ground up is where it's at as far as I'm concerned though... Link Removed
 
  • Like
Reactions: BurningSkies and jeff ward
#20
Passinwind said:
You could also just try using a 5751 instead of a 6SL7, the gain factors are very close and no adapter is needed

Building new amps from the ground up is where it's at as far as I'm concerned though... Link Removed
Click to expand...

My 12ax7 preamp has 5751's in it. 12au7's were a bit too low gain, but the 5751's sound great. I also tested them in my Champ and they made it have a tone more reminiscent of the classic bigger Fender amps.
 

Latest posts

Top Bottom
Back