Any 6SN7 Guitar amps?

[Cygnus X1]

This came up in my thread about KT88's.

Does anyone have a design for a very low watt, high preamp gain amp using a 6SN7?

Edit...I just found a thread in the search.
Any "new" info is appreciated, though.

[Phil_S]

Funny you should mention this. I'm planning something like a 5E3 but all octal. The 6SL7 is very much like a 12AX7, but it's gain rating is 70 compared to 100. I've got a used chassis already drilled for octals, and that's what got me to look into them.

The 6SN7, is so close to a 12AU7 that I would say any sort of self split 12AU7 design would work identically with a 6SN7. Have you looked at the Firefly? I think this is a project from AX84.com but can't be sure, as I downloaded it sometime ago. I think it is a public domain item.

As far as high gain, you may need to cascade several sections of 6SN7. With a gain factor of 17-20, this is not a high gain tube. I'm guessing, maybe you happen to have a bunch of these?

[Cygnus X1]

I've seen the firefly, wasn't all that impressed with the sound clips, though.
I'd be open to adding more gain, if someone has designed it, though.
I have ten or 11 6SN7's kicking around, all tested.
RCA's, Syvanias, etc.

I am a member over at AX84, but have a lot of trouble getting useable info from the site. There's a lot of dead links, too.

[muchxs]

There are some early organ amps that use 6SN7s on the front end. The difficulty there is that a weak B-3 hits the first preamps stages with around 4.5 volts of signal while the hottest guitar signal is under 1 volt.

I exchanged email with a builder in Texas who was building guitar amps with multiple cascaded 6SN7 stages, my burning question was, "Why?!!" The 6SC7 or the 6SL7 are much better suited to guitar preamp duties.

Big bottle drawbacks: The commonly used 12AX7 (or any 12A-7 series tube) have humbucking filaments. That means that any hum from AC filaments (in theory) is cancelled. The allegedly hi-fi miniature type 6EU7 (similar to 12AX7, different pinout) doesn't have humbucking filaments and the difference in medium to high gain circuits is noticable. 6SN7s, 6SC7s and 6SL7s don't have humbucking filaments.

I really like the SC7s and the SN7s, they're a thick sounding tube.

RCA 6SN7s are fetching big bucks on eBay right now, if it were up to me I'd grab the cash then spend some of it on NOS 12AX7s or perhaps some of the higher gain big bottle types.

[dartanion]

Here's a link to the Moonlight amp. Also, google that name and you'll find a few different resources.

The PI is LTP, push pull triodes, cathode biased. Very simple. Pull your preamp of choice from whatever amp and give it a shot. Something like this is a great first scratch build.

http://www.frontiernet.net/~jff/moonlig ... olume.html

http://www.amptone.com/delftmoonlightamp.htm

http://www.frontiernet.net/~jff/moonlig ... Power.html

[Cygnus X1]

You guys are awesome!
I'll look into the moonlight a little more.

Thanks

[rfgordon]

I recently built an amp whose first tube is a 6SL7 or 6SN7. To over-simplify, imagine taking a blackface-style reverb amp and replacing the vol/tone stack with just volume and the 5F2A tone control, and changing the first tube from 12AX7 to 6SL7. All this into a cathode bias 6V6 pair with no NFB.

Even though the 6SL7 is lower mu than a 12AX7, this thing will still grind hard, baby!

I tried both 6SL7 and 6SN7, and I like the 6SL7 better--seems clearer and punchier in this amp, not just gainier. However, since there aren't that many types of 6SN7 around, it could be that tube's personality.

The octals have a less fizzy top end than the 12AX7s, and they tend to be a bit fatter sounding. Some complain about the noise, but I ground the filament CT to the top of the 6V6 cathode for DC reference, and all is silently beautiful greasy grindage.

[dartanion]

I did a Plexi style preamp with 6SN7s once and it sounded great. Changed that amp to something else, then something else, you know the drill

These octal pres do sound really fat, however they tend to be microphonic.

[dehughes]

Komet Constellation...

[Andy Le Blanc]

6sn7's make great amps...... great old tube
theyll handle a lot power in the right application
great for hifi .....they are a "standard"...... the 12ax7 has
a very limited bandwidth and a lot of gain...... you might not like the
6sn7 with its very open tone .....
the only real drawback for guitar amps is the physical construction and
size of these large octal tube as a pre amp..... they're sometimes very noisey
and take a longer time to warm up....... you have to really take the time to
let the tube warm up....... that reverb tone in old ampeg reverberockets
was built around this tube..... I've seen em in old masco's and wards too.....
great 50's tone....

[Phil_S]

The allegedly hi-fi miniature type 6EU7 (similar to 12AX7, different pinout) doesn't have humbucking filaments and the difference in medium to high gain circuits is noticable.

Please understand that I'm not trying to be argumentative here; just looking for some clarity. I've used 6EU7 in place of 12AX7 for V1 on a couple of amps, with no noticeable issues. In particular, I chose this tube for my JTM45 because I had a Mullard looking for a socket.

What I am fairly certain of is that the difference between a 12AX7 and a 12AX7A is that the filaments in the 12AX7A are spiral wound to reduce noise, and that the 6EU7 uses the same spiral wound filaments. Is this what you are referring to as "humbucking"?

[Andy Le Blanc]

all indirectly heated emitters produce a small magnetic field that reduces
60cyl. hum.... most are helicaly wound..... some are folded.... 25l6
that spiral wound is nothing new..... its technically called a reverse helix
and makes a little bit more of a magnetic feild which supresses hum...
its not humbucking....

[GainMaster]

I've seen the firefly, wasn't all that impressed with the sound clips, though.
I'd be open to adding more gain, if someone has designed it, though.
I have ten or 11 6SN7's kicking around, all tested.
RCA's, Syvanias, etc.

I am a member over at AX84, but have a lot of trouble getting useable info from the site. There's a lot of dead links, too.

You must not be hanging around much lately Cliff and Jon have worked out a great sounding 6SN7 ouput section using the standard long tail PI and 12ax7. It is currently included in the October Studio schematic. You should be able to slap just about any high gain preamp to it if the B+ requirements aren't over 320v or so.

http://www.ax84.com/static/october/AX84 ... 080601.pdf

Before you ask there are two preamp schematics, one showing the vintage modern/switch and one showing the holy crap switch. The holy crap switch changes the front end from parallel to series. I have the only working model and used 470k for Rx1 and 58k for Rx2. Works great and has a tone similar to the SEL. The original values should work too just that no one has tried them.

This weekend I'm starting to build a mini-wreck using the same output section.

Brian

[GainMaster]

I've seen the firefly, wasn't all that impressed with the sound clips, though.
I'd be open to adding more gain, if someone has designed it, though.
I have ten or 11 6SN7's kicking around, all tested.
RCA's, Syvanias, etc.

I am a member over at AX84, but have a lot of trouble getting useable info from the site. There's a lot of dead links, too.

Here is a link that isn't dead

http://www.ax84.com/static/october/AX84 ... 080601.pdf

I have built one and it sounds great. Currently working on a mini-Wreck.

Brian

[ic-racer]

Its not high gain, but it sounds better than my Champs. I have a single 6V6 type Valco/Gretsch with a 6SC7 pre tube. I drew up the schematic a while back and can post it if interested.