octal preamp

[andrew]

Has anyone had experience using a 6SJ7 octal preamp tube?

[tomrasdf]

I've been wondering the same thing. I know Alessandro uses them and apparently with some success, but I've never had any experience with them myself. I'm very curious to hear anyone's thoughts.

[doctord02]

I built a hybrid amp that was a mix of the Moonlight power stage (6sl7 phase inverter and a 6sn7 dual triode running as a push-pull output) and an Octal Fatness pre that used a 6sj7.

Was kinda cool but I didnt fall in love with it and didnt have the patience to fully tweek it out so I rebuilt it with a 'wreck preamp and really did dig on the way that turned out.

The 6sj7 is a cool inexpensive way to play around with a pentode preamp tube. Here is a link to one of David Jones' schematics that uses the 6sj7:

http://www.diyguitarist.com/Schematics/ ... s-Full.jpg

and here's Dave's other schematics and such:

http://www.freewebs.com/jonesamps/jones ... matics.htm

[UR12]

Has anyone had experience using a 6SJ7 octal preamp tube?

I love the sound of the 6SJ7. Having said that, it's hard to find one that isn't microphonic, I would also recommend running the 6SJ7 or 6SL7 on dc heaters to avoid some of the hum. I have an amp I just built using the 6SJ7 and 6SL7 for one channel and an Express preamp for the other channel. The Russian 6SJ7 and 6SL7 are pretty good tubes as long as you keep the gain under control to prevent squealing and oscillation. Oh yea, the power section of the amp is using a dual single ended EL34 configuration with fixed bias.

Here are some clips

This is just the Octal channel by it self. A little chickin pickin, Brad Paisley kind of tone with a Tele.

http://users.zoominternet.net/~jdhall/a ... le%202.mp3

Here is a clip of both the octal and Express channels combined.

http://users.zoominternet.net/~jdhall/a ... 20tele.mp3

[funkmeblue]

I had bettet luck with the chinese 6n9p than the sovtek 6sl7.....

[mhuss]

Here are some clips

Hmm, sounds a lot like Richie!

--mark h

[UR12]

Yep, its Richie. He swears he's going to get Bud to do the next ones

[andrew]

Mr. UR12, great clips! What power section set up is that? What is the trans voltage and OT? My single ended Rocket preamp-Adams SE power section is on hold due to a dead OT somehow. Until I get a new one I might want to build an octal after all! Thanks, Andrew

[UR12]

Mr. UR12, great clips! What power section set up is that? What is the trans voltage and OT? My single ended Rocket preamp-Adams SE power section is on hold due to a dead OT somehow. Until I get a new one I might want to build an octal after all! Thanks, Andrew

Andrew

This amp was a group project. The power section is running 2 EL34 in parallel single ended. Voltage runs about 400v. The OT is a customed designed 2.5k SE airgapped tranny that we had Heyboer make special for us. There was nothing off the shelf that we could find to do the job. It is also running fixed bias instead of cathode bias and pumps out about 30w. The amp is still in the prototype/testing phases so I am sorry I am not at liberty to supply you with schematics.

[andrew]

When it's finished will you publish the layout in Ampgarage?

[UR12]

I'll see what I can do and if the group doesn't mind it would be fine with me.

[David Root]

I can second the comment about using DC heater supply on octal preamp tubes. I built a 4-6V6 amp with five 6SL7s as pre-s and PI and I finally put DC on all the heaters, (including the 6V6s, which probably wasn't necessary), but it killed the hum dead!
I think we are so used to the 9-pin 12A*7 series and related minature noval types, that have the humbucking heater connection "option", that it doesn't occur to use DC heaters on the older octals which don't have the humbucking wiring option, UNTIL you actually try it!

Alessandro uses octal pre-s because the bigger glass gives a more spacious tone. However, he also uses Black Gate power supply caps, which would have something to do with that too. But that's a whole different post!

[Johnhenry]

Sharp-cutoff pentode, Very good sounding amp Dana, you hook the 6SJ7 up as a pentode or a triode ?, My experience with octal's are bout the same, some are microphonic, some not so much, I just finished a very old Electromuse 1X12 combo for a Harp Man, Had 2 X 6SJ7's & 2 X 6V6's turned out very nice, I do know this, set up right, octal's are very touch sensitive to the Guitar, I have a great collection of octal tube's, if you need some and I have the # I'll donate some for this thread, I have a very large old tube collection, and what's sad I still have to buy a few here and there, You just never got all ya need !
John

[andrew]

Could I use a 12SQ7 in place of a 6SJ7? It's an old RCA.

[unklmickey]

Could I use a 12SQ7 in place of a 6SJ7? It's an old RCA.

goodness no, Andrew.

they are entirely different types of tubes, even the heater connections are in the wrong places.

if you did that, you would almost certainly destroy things.



unk