6sl7 front end

[passfan]

SUCCESS AT LAST. I found a problem with an older multi can cap and once eliminated the power tranny cooled down and the hum is gone. This thing is one clean sounding bad mamba jamba. I can run the gain all the way to the stops with not one ounce of noise and get the cleanest AC/DC style breakup I've ever heard. This thing is so clean and chimey you'd swear it had reverb.
I am running JAN 6188's for V1 and V2, a russian longplate 6SL7 (brand unknown) for V3 and old stock RCA 6L6GC blackbases on the output, with an old stock Baldwin 5U4G rectifier.
I pretty much followed the rocket preamp circuit until the PI, which I borrowed from Aikens site, into a pair of 6L6GC's. The PT is 350-0-350 which is rectified and then runs through a series of filters RJ style (80,40,20,20,20) using 10K resistors instead of 9.1k. My B+ is around 412 and I used a 158Q choke. Now that my PT has cooled down I may replace the choke with a 1k 25 watt and try for some sag. This turned out better than I had hoped as I think I like it better than my Rocket.
I will take some time to play it and then post some pics before I commit it to a permanent chassis with a turret board.

[M Fowler]

I was really wondering why your Rocket was giving you problems its a very quiet circuit to begin with. Glad you found the problem.

Octal preamps sound fantastic.

Mark

[passfan]

I was really wondering why your Rocket was giving you problems its a very quiet circuit to begin with. Glad you found the problem.

Octal preamps sound fantastic.

Mark

Yes they were the old style that you twisted and soldered the ground pins to the chassis. I twisted the tabs but forgot to solder them. I replaced them all with F&T's.

[M Fowler]

If I do use the twist mount type can cap I punch or drill a larger hole for the twist caps to go through the chassis and then use a clamp rather than the twist mount system.

Mark

[FUCHSAUDIO]

The only issues are finding quiet and non microphonic tubes. The operating points are pretty close to the 12AX7 for a 6SL7 and the 6SN7 is more like a 12AT7.

I made 8 to 9 pin adaptor bases and put 12AX7's in 6SL7 sockets on more than a few B-15's in the 80's

I find mounting the sockets on grommets, putting heatshrink around the body glass, even putting an aluminum Bud cover box over them can help a ton.

Sovtek was talking about introducing a premium low noise 6SL7 (or claimed they were working on one), but I don't know if that ever happened. Love big bottles like that, something organic and fat...

[FYL]

The operating points are pretty close to the 12AX7 for a 6SL7 and the 6SN7 is more like a 12AT7.

6SL7 => 5751
6SN7 => 12AU7

Sovtek was talking about introducing a premium low noise 6SL7 (or claimed they were working on one)

It already exists: it's called a 1579 and is (was?) manufactured at Reflektor!

[passfan]

The only issues are finding quiet and non microphonic tubes. The operating points are pretty close to the 12AX7 for a 6SL7 and the 6SN7 is more like a 12AT7.

I made 8 to 9 pin adaptor bases and put 12AX7's in 6SL7 sockets on more than a few B-15's in the 80's

I find mounting the sockets on grommets, putting heatshrink around the body glass, even putting an aluminum Bud cover box over them can help a ton.

Sovtek was talking about introducing a premium low noise 6SL7 (or claimed they were working on one), but I don't know if that ever happened. Love big bottles like that, something organic and fat...

Thanks, I'm not experiencing any problems with my prototype yet even though I can tap the chassis and hear V1. When I commit to a permanent build I will certainly use your advice to gain every ounce. I already went to a 6SN7 in the PI and think I like it better than the 6SL7 though that could be the difference of brands as well. It did take some edge off the breakup though the bottom is a bit muddy at full on. Something to work out I guess.

[passfan]

any chance for some gut shots,i've been wanting to do something like this for a while i would love to see.please and thank you

Finally time for some shots.

[passfan]

And a top shot.

[M Fowler]

Great job on the PTP, I like.

[lumox0013]

very nice, hard to tell all the conections w/ it being ptp but +1 on th layout especialy being a proto. I've been all over aikens page looking for info on the PI since you posted cant seem to find any thing which section should I be in ? thanxxx for the shots& congrats I bet its ssweet & cclean

[ampgeek]

Aiken site: Technical Info--->Advanced--->Two articles on LTPI. One of which uses the 6SL7 as a model.

I built a Bassman 5F6A with all octal front end. I used 5691s (industrial 6SL7) and it was very stable and quiet. Lovely souding amp!

The connections and components were just as specified for the stock 12AX7 plan but adjusted for the pinout difference. Worked great as is.

I did go back and tweak some of the components ala Aiken but returned right back to the standard because it sounded better.

Good luck!
Dave O.

[passfan]

Okay I just spent the afternoon playing and setting up each amp I've built , tube wise. I went from the Rocket to the Express to the 6sl7 Rocket using the same cabinet and guitar, changing out tubes in order to get the best sound out of all of them and when I got to the 6sl7 I was blown away. It has better chime and a much cleaner and smoother breakup than either the Rocket and the Express. So much so I wonder why Ken never used them.
I jam the gain all the way to the stop and use my guitar volume to control it, it's amazing. I thought about using the unused triode for another gain stage like RJ did but wide open it doesn't need it as it sounds as gritty as a JCM 800 balls out but back off your guitar volume a couple numbers and your back to AC/DC. One more number back and your into a really clean chime. I held a note this afternoon until I thought it wasn't going to stop and let it go. I'm loading this thing into a proper chassis with some decent iron and parts. It just became my number one. I'm working with a new program right now to record some tracks into my computer so I'll try to post some clips later.

[RJ Guitars]

Passfan,

That sounds encouraging. I've got a buddy who tries to build every amp using Octals so 6SL7's are usually part of the line up. He just loves those tubes! They are a famous for great tone but also some hum, and microphonics. If you found a quiet set then you've scored big. There is somebody that has those in production again, right?

Do you think the difference of the gain plays a role in your results? I think it's 70 on a 6SL7 vs. 100 on a 12AX7.

Congrats on putting together something that works really well. It really looks like something in the true spirit of Ken Fischer.

rj

[FYL]

There is somebody that has those in production again, right?

New Sensor offers Sovtek and Tung Solski Russian versions, based on the old 6H9C, itself "inspired" by vintage 6SL7 US designs. The Sovtek is a rebranded 6H9C, the Tung Solski uses a slightly different structure.

The 6H9C is still manufactured in Russia and available from various sources, as is the Chinese 6N9P - J grade is really nice.

Re. NOS tubes, a large number of Philips ECG 6188's (aka. 6SU7 / 6SL7WGTA, a premium Mil version) are currently available at decent prices. Made in the former Sylvania factory and bearing 86XX date codes, they must be some of the last of their kind manufactured in the US of A...