Opinions on 6SL7, 6SN7?

[boots]

Anybody have any preferences amongst the octal dual triodes? I have a bunch of old 6SN7s' and a couple 6SL7's. Thinking about using them someday in a tweed-ish build.

I understand the octal preamp tubes have a fatter, richer sound than the 12AX7 family. Is that true? Do you guys have any experience with them? I know that the 6SC7 was widely used, but it has a different pinout. It would be nice to be able to swap SL and SN into the same sockets for taste testing.

Was the SC sweeter sounding than the SL & SN? Is that why they were seen more in the old amps? Is it worth designing an amp around the 6SL7 and/or 6SN7?

[Phil_S]

I think, in some respects, the answers are rather subjective with respect to tone. Take a good look at the spec sheets and you'll get more than just a few hints about the tubes, but some of it is subtle.

The 6SN7 has specs that are almost identical to 12AU7. Aside from one being octal and the other noval, they will interchange very well. The big differences are 1) 6SN7 has a maximum plate voltage of 450, which is well over the 12AU7, and 2) the physical plate size is comparatively enormous. These features make it decent low gain preamp tube, but it can really excel as an output tube due to both of these features. Try a pair (4 triodes) in PP for a 10-15W amp -- it makes a great clean tone. Half of one of these makes a good concertina.

The 6SL7 is a bit of a different tube. Let's call it a first cousin to the 12AX7 and 5751. Gain is more like the 5751, but plate resistance is lower. It is good as a gain hole tube and by tweaking plate and cathode resistors you can probably milk quite a bit of gain from it. It is probably not nearly as good as a 12AX7 for a tremolo oscillator due to the lower rated plate resistance value.

[9pins]

6sn7 is a grand old tube, great for pre, I love them as inverter after a simple 6sj7 pre, also really good as a driver after a inverter because it can handle some current.

Depends on what you end up with a gain structure, and what the power tubes require for a driving voltage. The large plate structures can be microphonic and take a while to warm up.

I think the 9 pin equivalent is the 6cg7, and if you need a larger current handling you can go with a 12bh7

[passfan]

I have built three Rockets using the 6sl7 and twin 6L6's on the output. They sell really fast. Very chimey amps.

[FUCHSAUDIO]

Other than microphonics, the octals do have a certain warmth and organic nature that is cool. It's difficult in higher gain circuits to find quiet and non microphonic tubes. I like to mount the sockets with grommets (old school style), which can help alot. The 6SN7 push pull (Use the Mojo 1580 output) makes a wicked little push pull output.... . 6SL7 is like a 12AX7 and 6SN7 like 12AU7. The same circuit values do work.

[skeezbo]

I had to sort through about a dozen NOS 6SL7s in order to find two for a B-15, and they were still pretty microphonic. Has anyone tried the new Tung-Sols? How do they compare to the vintage?

Skeez

[FUCHSAUDIO]

I had to sort through about a dozen NOS 6SL7s in order to find two for a B-15, and they were still pretty microphonic. Has anyone tried the new Tung-Sols? How do they compare to the vintage?

Skeez

I make an adaptor with epoxy, an 8-pin tube base, and a 9 pin socket to put 12AX7's into B-15's. They can be very difficult. In the 70's (when you could still buy brand new GE or RCA tubes) I would get a box of 50 and maybe get 5 to 10 that were tolerable. I asked an old Engineer friend of mine about it, and he basically said "deal with it, microphonics have been around since tubes were invented"

[boots]

I've heard they can be microphonic. Do you think that is true of the glass envelopes (GT-suffix) as well as the metal versions? Are they all microphonic?

[M Fowler]

I use new production tubes and they work quite well. Also chinese tube companies have good sounding non-microphonic tubes I used in the Gibson EH150 build.

Mark

[boots]

Thanks for all the good comments. Does anybody have any experience with the 6SC7? I know it has a different pinout than the SL. I'm trying to decide whether to use the SL's I have or hunt for some SC's.

[Phil_S]

The 6SC7 has a shared cathode for both triodes. The 6SL7 has two cathodes. Internal plate resistance is 53K for 6SC7 and it is 44K for 6SL7. Otherwise, probably not much difference. I think I'd prefer to have separate cathodes. If you need an oscillator tube for a tremolo, stick with the 6SC7 for the higher Ra. 44K is on the low side for a tremolo circuit.

[M Fowler]

Fenders use of this in an early bassman 5b5 I think is a good platform for 6SC7.

I also use the 6SQ7 tube as well.

Many circuits used these octal preamp tubes and while a production amp might not be able to keep up with tube quality a home built amp with octal preamp tubes would make a good blues/jazz amp to have around.

Mark

[surfsup]

I got a couple 6SN7s off the bay and used one as an input tube (cascoded both triodes) for a recent amp build. Gain is 160+ measured on the scope. No microphonics, and sounds very nice. Very open and "airy"' amp. Bass is punchy, highs are quite smooth. Currently my favorite amp in terms of versatility.

I plan to use the other as an output or get another and do parallel 6SN7 outputs.

[JamesHealey]

Where i work at wienbrock amps we use the 6sn7 as an output tube to great use!

[boots]

Thanks for all the great input, guys.

I will eventually get around to building up an amp most likely using the 6SL7 for V1. It may be a while in the planning stage, but I will post something on here when I get it together.

Sounds like the 6SL7 is the best choice for the preamp. I have a couple NOS GT examples, and will keep my eyes open for more.

I do have several 6SN7's that I probably won't end up using, if anybody needs them. One is a GT and there are at least 2 GTB's, which have the coin-base. They are funky-looking, but they look to be made by RCA, judging by the octagon around the number. They are untested, but were probably pulls out of some military surplus gear that my uncle had. I scored some other pulls from that old gear, and they have all turned out to be good tubes.