6SN7 line stage project?

[JimJ]

http://www.geocities.com/northbirdten/line_stage.htm

I found this while surfing...seems like there's a lot of info out there on tube rectified, dual 6SN7 line pre's.

Does this look like a decent schematic to follow? I like the idea of 6SN7's because they're still in production...even though they'd be more expensive than 12B4A's for example.

Thanks :)

[95Honda]

6SN7 is a killer little tube. I really liked the sound of them in our Mana mono-blocks we built at Audioprism. Rugged with a long life the way we ran them also, IIRC....

[MikeS]

looks like a simple cathode follower circuit I think.
Wouldn't be very difficult to breadboard the schematic.

But there is a few bucks in that PS. A rather large choke, plenty of capcitance, DC heated, etc....

6SN7 is good sounding tube I suppose. My Aikido linestages sound smooth and open with plenty of gain. Almost too much gain.....two o-clock and over on the volume pots will pinch all the amps I try. Under 2 o-clock and things sound sweet.

Keep in mind that 6SN7's can be microphonic little pigs. I dunno if your going to use new russian 6SN7's and how microphonic between samples they are.
Maybe they have cured that issue.

I use some green label Sylvania chrome tops. Roughly late fiftie tubes pulled from a organ at St.Vinnies.
My local audio buddy pinched around 25 or more of them.
We tested the tubes with a mutual conductance tester and a emission tester for all the usual things except microphonics.
Maybe a spendy Hickock has that feature.....

We tested for microphonics in circuit. Yank one, put one in, let it come up and tap on it. 15 or so tubes tested strong out of the 25. Roughly, 5 or 6 passed with low microphonics. Some pinged...some clanged...one just screamed away until it was yanked.
Some feel it's a bad thing to tap on tubes to test for microphonics, and will do internal damage to the grids or whatever.
I feel if the tube can't take a good tap or three without damage, then it was a POS anyway.
I can understand with some ol' rare pair of 45 globes, it may not be good to tap on 'em too much.
But a 6SN7? Who cares, they made a billion of them.....
And 6CG7 is a 6SN7 in a nine pin minature bottle.

I still want to play with the 12B4A in a linestage. My half-assed one-sided cobble-up a 12B4A linestage didn't sound too bad really, enough to try again... They can be microphonic as well.
The RCA 12B4A sample I have clangs a bit when tapped.

5687 is another tube that would fly in a linestage. The Tung-Sol I tried had a good sound, but did the whistle. I tried the little ferret beads and suppression resistors, but I think the tube was just not quiet enough for line-level use.

My Aikido's do need PS work to get lower noise levels for use with the 2A3 amp. They are fine with the Push-pull 6BQ5 amps, and single-ended 6BQ5 amp. But too noisy with the triode amp. But gain is fine with the SET amp using a 100K stepped attenuator.

There is a bit more life using a active linestage, I'll admit that.
I found a 250K pot to try in one of the Aikido's to replace the lower 100K resistor with the second 6SN7 in the Aikido circuit.
Use it as a null pot to maybe get less noise. PS redesign would be the best bet....
I need to get this Eico back together, I'm curious to hear the beast. It better kick triode bootie dammit!

[95Honda]

The little 3-M tube dampeners work good for microphonics. I use to use them alot, they were a round little ring that was made of a high heat visco-elastic composite of some kind, some were clear and some were black. They seemed to do the job good. I would put 3-4 of them on each tube...

[JimJ]

It better kick triode bootie dammit!

Somehow, I doubt it :)

[MikeS]

Somehow, I doubt it :)

Heh.....
Yeah, I'm pretty sure the Eico won't do the liquid midrange, and probably won't do the big stereo image as well.

But I gotta have my headbangin' thrash and grindcore fix. Some of it sounds rather fine through the 2A3 SET amp at moderate levels. And some of it sounds pretty disgusting as well.
It doesn't necessarily have to heavy metal recordings. If it's bad, it sounds bad.

I'll always be partial to the sound of a single-ended triode. The 2A3 amp is the most involving of all my junk amps.
But I want to be able to really boogie beyond where the SET amp pinches.

Thats where the Eico comes in. It claims seventy watts, but that's maxxed out clipped on a scope.
I'd probably won't be listening past 20 watts per side cranking hard with the Cornwalls if that.
As long the amp sounds clean and balanced with good strong bass, it should do fine with death metal. I hope a lot better than the broken glass sound of a 30 wpc SS integrated amp when pushed trying to jam..... or the grainy static spit of a tweeter...

I've wanted to build or find a higher powered push-pull tube amp for some time, just to hear if anything.

I listened to a stock rebuilt Dynaco ST-70 for a few weeks with Hovland coupling caps, and EH EL-34 tubes.
The amp boogied and measured well on the bench, but the midrange was rather dull, and the bass was soft. If I had bought the Dynaco, I would have certainly modded the amp.

But 450 bucks was too rich considering I still would have to rework the amp....fuck that.....I have 100 bucks into the Eico pretty much fully rebuilt. The amplifier driver topology is a bit better than the Dynaco ST-70.

Mike has nice stock example of a older Dynaco ST-70.
Which I hope he will keep in stock condition considering how many of these amps get desecrated and rebuilt and modded over and over and over by many loons over the years.
Old working versions of stock Dynaco ST-70's in good condition are probably getting to be a rare thing. But they did make many....

95Honda,
Did you use the 3M tube dampers while you worked at Audioprism?
Have any idea where they were sourced?
I'm curious to try one on a 6SN7 now. I've seen tube dampers on the net, they always seem spendy for what they are.
The Pearl tube coolers are rather expensive and look like a iron maiden for a poor tube......

[95Honda]

Michael Percy has some for 60 cents each, pretty sure they are not the same ones as we used, but they looked close