Aikido 6SN7 amplifier

[Mike Stehr]

I took a chance and used this schematic (or really SPICE simulation) and threw all this crap together and made two mono linestages at minimal cost to hear what they would sound like. Ain't pretty, but the circuit seems rather promising.....

 

[WhiskeyRebel]

No grid to ground resistor on the input?

 

[Mike Stehr]

There's a suppessor resistor.......

 

[tcdriver]

What is the purpose of R3, R5, R6 and R7? How much gain does your line stage have?

 

[Mike Stehr]

From what I can understand, the one meg resistors are safety divider resistors.
The first divider protects the CF tube if the input tube is yanked, the second divider protects the stage after the CF if that tube happens to be yanked....sumthin' like that.

I think,(and am probably wrong) that the gain is ten. The formula I think is on the TubeCad site, I thought I wrote it down but I can't find it.
There is other equations for the dividers, PS ratios, etc....I need to sit down, measure and ponder them out.

 

[tcdriver]

Which triodes share a tube? Do you put a DC bias on the high side triode heaters? Do you use DC or AC on the heaters?

 

[Mike Stehr]

Which triodes share a tube? Do you put a DC bias on the high side triode heaters? Do you use DC or AC on the heaters?

Triode sections one and two on the schematic are one 6SN7, sections three and four are the second 6SN7. That's the way I did it.

The linestages are AC heated. I'm using the 6.3 volt filament windings from the PS transformers, which are RCA units from single-ended 6BQ5 amplifiers.
The windings fed two 6BQ5's and a 6EU7, so heating two 6SN7's shouldn't be no issue with regards to current.

The 6SN7 heaters are parallel wired, with two 300 ohm resistors to the main CT ground point off each leg of the filament winding. They were noisy as hell floated.....like a open patch cord. Plenty quiet now.

http://www.tubecad.com/2004/blog0011.htm

http://www.tubecad.com/2004/blog0013.htm

http://www.tubecad.com/2004/blog0016.htm#MoreAikido

http://www.tubecad.com/2005/January/blog0030.htm

http://www.tubecad.com/2005/January/blog0032.htm

http://www.tubecad.com/2005/January/blog0033.htm

 

[kyle]

this is becoming a popular design

There seems to be lots of people doing this one now. I like it because it worked first time and it's quiet. Oh, it sounds good too.

I stuck a photo of mine in the galleries a couple of days ago.

 

[Mike Stehr]

"There seems to be lots of people doing this one now. I like it because it worked first time and it's quiet. Oh, it sounds good too."

Same here.

That's a damn good looking Aikido 6SN7 amplifier there.

What brand/type/value of caps are you using for the output?
I'm using 2 uF 400 volt Solen metal polyprop's until I can try something else....

 

[kyle]

I've popped in solens, vintage relcaps, wonders, and I'm back to the solens right now. I have a bunch of Russian teflons that will go in sometime later.

 

[Mike Stehr]

I've popped in solens, vintage relcaps, wonders, and I'm back to the solens right now. I have a bunch of Russian teflons that will go in sometime later.

Interesting.....I do have some older higher voltage oil caps I can try, provided they won't leak too much DC......

Thanks.

 

[Mike Stehr]

They may be butt-ugly, but these left and right mono Aikido linestage amps sound rather good with that little SE 6BQ5 amp. Like left and right turbo power.
I'll have to make a stereo version.....