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Re: 6SL7/6SN7 vs 12AX7

6/8/2003 3:52 PM
Al Nelson
Re: 6SL7/6SN7 vs 12AX7
I just finished an amp that uses a 6SL7 as the PI and I like it a lot. I also have one as a parallel gain stage on the clean channel. Both are WXT variants - military/rough duty spec. They sure have a lot of sonic meat on the bone.  
As you probably know, the 12AX7 was modeled after the 6SL7 and the 12AU7 is based on the 6SN7. That one is also a really good PI if you already have enough voltage gain - it doesn't have as high of a mu as the SL - but it can manhandle more current. Very nice with EL34's.
7/7/2003 11:00 PM
Rob Mercure

Well - while is isn't inaccurate to state that the 12AX7 was "modeled" on the 6SL7 being another tube with two high mu triodes each actual triode was modeled on the 6F5-6SF5 single triode octals.  
6/5/2003 4:39 PM
Certainly cool! Those adapters are a great idea. Do they work in all 12AX7 circuits or are there some limitations?
6/5/2003 4:44 PM

I have not run across a circuit that they couldn't be used. Obviously, you would not want to put them in something like a dual rectifier or SLO 100 because they would squeal like mad.  
6/8/2003 7:01 PM

I built a 6V6 push-pull amp with a 12AX7 in one channel and a 6SL7 in the other (with a balance control between the channels). It allows an instant comparison. I find that I mostly lean towards the 6SL7. They are definitely different. But if you have a 12AX7 amp already, you can also try substituting a 12AY7 or a 5751. At one point I had a 5751 in there that sounded very much like the 6SL7.  
6/19/2003 2:10 PM
B Romanuk
I've built a couple of 5E3's and I always use a 5691 as the pre-amp tube. I leave the phase inverter a 9 pin. All of the people who I've built amps for like the sound of a 12AT7 as the phase inverter in their 5E3, myself included. There is no point in using a 6SL7 in the phase position. Use the best 5691 you can get in the pre-amp, and use the 12A-7 position to set the amount of gain you want. I've even built a marshall 18 watt using a 5691 in one of the pre-amp channels. I know that the red base 5691's are expensive (I happen to have 50+ of them by diff. manufacturers, I found the big plate ECG/Phillips to be on par) The small plate versions seem to be microponic, at least the few I tried.
6/21/2003 9:09 PM

i made a 50watter homebrew. It's pretty much a marshall with two 5881 in the power section and a 6sj7 in the first gain stage, set up like a fender champ. i didn't do it to be cool, is it cool? those were just the tubes i had on hand. i also put in two relays that switch in/out two different gain and volume pots, so its sorta got two channels. well two of the exact same channel, but i tweak the gain/volume opposite for each channel, so one is dirty and one is clean.  
any opinions? thanks
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