6SN7 or 6SL7?

[Madison]

Which do you prefer in a SE amp with a single 6V6?
Is one better than the other for guitar amps?
I am looking specifically at the Sovtek brand.
I have always used 9 pin preamp tubes but want to try something different.
I hope I don;t have to beef up the PT to accommodate?
Any info on this,or even a schematic for a good guitar amp, would be great.
Thanks

[labb]

Take a look at the Fender Princeton 5B2 and/or 5C2. SE, 6V6 and 6SL7.

[plexi50]

6SL7 has more gain but is also more distinct with a sweet flavor. I love the 6SL7

[bigdaddy]

If you really want a great sounding amp with tons of gain that could be tailored for yourself think about this.

Use a 6SJ7 pentode similar to the early tweed champ(although set up differently) and put either a 6at6/6av6 or half the triode of a 6SN7/6SL7 or even the smaller dual triodes like the 12ax7 in front of the pentode. That's what I did with an SE amp and I put the tone stack in between the triode and pentode, just a simple fender BF setup. What an amazing sound!!!!!! the gain of the pentode really drove the power tube nicely, much better then a half of dual triode tube. Then the first stage could be really dialed in. The pentode sound is a much more pleasing form of distortion when driving the power tube.

Also the pentodes have a feature that not too many people use or seem to bother with. Some call it a squish control. If the pentode is set up correctly you can use either a pot or resistors on the (G2? pin 6 not sure) to ground. I don't remember correctly after the cap or before it, I'm not sure I don't even know if I have the schematics anymore since my amp days are over. But it controls the gain to change the drive to the power tube. It really works great when the pentode is setup right. I just don't remember off hand how to set it up, but it's on the internet. I built one in a 5F2 chassis and 4x8 combo cab but without that control. Anyway the amp sounded amazing, the extra gain helped drive those speakers(old Jensen C8Rs) but without getting muddy. I had to part it out on ebay....oh well.

[FYL]

Here's a partial schemo of a pentode/triode front-end using a squish control, from AX84 (Blues preamp).

[Madison]

Super. Thanks guys.
Okay I will go with a 6SL7.
So without the added triode stage your opinion would be that the gain of a single 6SL7 tube would be too low?
I am trying not to add another tube if possible on this build.
This will be going into an 8" speaker.

Now, if I could find a layout for a 5C2?
Correction, 5B2
Just based on quickly comparing schematics, I wonder if just a regular 5F1 board layout will do the trick?
I have that one ready to go.

[bigdaddy]

You can squeeze a bit more gain by going with 220K plate resistors and making sure the voltage on your plate is around 190V-200V. Also using a baxandall/James tonestack over a typical BF Fender will help. I am not a fan of just a tone control for many reasons.

But you just don't get that gain you'll get with a 12AX7. It's a bigger fatter sound but will not drive the power tube like a higher gain 12ax7 will. In fact you just might have too much in the mids with that tube. Honestly I would add a 6av6/6at6 and maybe use the 6SL7 or 6SN7 in a cascode setup and the single triode as the driver. I did that also and it worked well.

There's a lot of things you can do but many times just a good old 12ax7 works best. The other setups require a lot of dialing in and are more sensitive to speaker changes. But you might end up with something special and different, that's the great thing about building amps.

[jojokeo]

Also the pentodes have a feature that not too many people use or seem to bother with. Some call it a squish control. If the pentode is set up correctly you can use either a pot or resistors on the (G2? pin 6 not sure) to ground. I don't remember correctly after the cap or before it, I'm not sure I don't even know if I have the schematics anymore since my amp days are over. But it controls the gain to change the drive to the power tube. It really works great when the pentode is setup right. I just don't remember off hand how to set it up, but it's on the internet. I built one in a 5F2 chassis and 4x8 combo cab but without that control. Anyway the amp sounded amazing, the extra gain helped drive those speakers(old Jensen C8Rs) but without getting muddy. I had to part it out on ebay....oh well.

The Squish control isn't for a gain control rather it's a compression effect that you get w/ it. As it's name implies to "squish" is to "compress". I built it in once to try it and didn't think much of it and removed it. I instead made a variable gain control by putting a pot on the cathode resistor w/ a cap similar to a presence control. This works very well in controlling and varying gain on a pentode.

[bibi]

to each his own, I guess.  For me, the "squish" control is essential because it allows for a control of the low frequency output of the pentode as well as gain.  If you put large enough pot in, say 500k to 1M, the amount of control is really useful especially when the pentode is fully bypassed. 
It doesn't really become a compression effect for me unless there's a large signal driving it. 

[jojokeo]

I may revist it at some point to try it again but I got the idea and schem from AX84 about 2 years ago. This was when I first began playing and using pentodes and it did compress the signal as described. But, this wasn't what I was looking for or wanted at the time. I wanted an old school AC4/AC15 w/ lots of gain. Back then, the new Heritage Vox models were just coming out and there was very little info on pentodes on AX84 or this site. Since then, there's been a whole lot more. Especially since the 5879 tube and amps have been focused on by many here.

[bigdaddy]

That's the way I was using it bibi. When I tried it as a so called squish control I found it useless but when I figured out how to use it as a gain control with an EF86 it opened up a different approach. It was done by trial and error. It does NOT work with all pentodes. I tired it with the Pentode side of a 6U8A and it did not work at all. I think it must have to do with things I do not know nor understand.

That's what it's really all about, trial and error, for me mostly error. But when I get something working it works well and sound good to my ears.

I made this kickin' dual EF86 preamp driving an EL34, I used that gain control on the second EF86 and it changed the sound drastically, making it go from more of a VOX sound to a Plexi sound. Alas it tis' no more...parted out for ebay....

[jojokeo]

I have seen and read about but not tried connecting the screen's capacitor to ground/cathode. It was in an amp that had this option switched but made variable. I've wondered how this would sound and didn't get a very well described answer in that it made it sound "different". When I hooked it up as the squishy control it was w/ a 1M pot meaning it was w/ a high value as mentioned by bibi and suggested by AX84. At the time, the EF86 was in position V1. It makes sense that it would alter the frequency response as noted because it is exactly what that cap is for when designing the tube's frequency response as noted in various spec sheets. Now, I have a dual EF86 preamp amp but since the mod was made to fit into a vintage Fender chassis, I won't drill any holes to permanently alter a vintage item. So I can't play around trying this on the second tube unless I make it floating or maybe mount it somewhere else if it's worth keeping? Hmmm...???  :icon_scratch:

[panhead]

Here's one I built with a 6SL7 and EL34. You can use smaller iron - like Champ size - with a 6V6.

[bigdaddy]

Does that 1K screen resistor get hot? I had that issue and went to a 1.5K and 2K dropping resistor and the heat issue stopped.

[jojokeo]

Does that 1K screen resistor get hot? I had that issue and went to a 1.5K and 2K dropping resistor and the heat issue stopped.

Running at .081 watts and using 5 watt resistor - it should be cold.

[panhead]

It doesn't run hot. At least not like a power stage cathode biasing resistor.