Octal Aikido? What tubes?

[jayme]

I've got an all 6SN7 aikido linestage, and it just sounds so good that I've been unwilling to mess with it.

However, I have a couple alternative tubes sitting here: 6BX7s and 6080s.

Anyone try any non-6SN7s in an octal aikido?


My power transformer has enough heater current for any combo of these tubes, and I can easily adjust my B+ from 324V downwards to about a 200V minimum using a resistor/cap PS stage.

I've currently got the 6SN7s running at 324V B+, with 1000R resistors biasing the input tubes to ~4mA and 330R resistors biasing the output tubes to ~11mA. (Pretty much exactly what Broskie recommends for the 6SN7s...)

If I were to drop the 6BX7 or 6080 into the input stage, I'd lower the input tube bias resistor to 500R, and adjust the B+. In the output stage, I'd pretty much leave the biasing resistors as-is, change the B+, and change the PS-noise injection resistor.

 

[Sheldon]

I trust you are using this table:

http://www.tubecad.com/2006/05/blog0064.htm

 

[jayme]

I am indeed using that table.

 

[aletheian]

I built a 6SJ7/6922 Aikido. Sounded great!

 

[Giaime]

Hello Jayme,

you have a beautiful name

I heard the Aikido with 6SN7 frontend and 6AS7 output. It was at a friend of mine's house, he had to drive about 5m unbalanced cables up to his power amps, near the speakers. So he needed lowish output impedance. It did sound quite good, but I wouldn't suggest it if you haven't those particular needs.

But as far as I understand, the most important tube choice for Aikido is the first tube, the output tube does make a difference but not greater than swapping around a couple of brands of 6SN7 (I like russian ones...).

Just my 0.02€

 

[Sheldon]

But as far as I understand, the most important tube choice for Aikido is the first tube, the output tube does make a difference but not greater than swapping around a couple of brands of 6SN7 (I like russian ones...).
Just my 0.02€

I would think (without any direct experience myself), from a design standpoint that this would logically be so. The first tube sets the gain and does the voltage amplification so it will largely determine the character and distortion profile of the amplifier.

The second tube functions as a buffer, and as long as it can provide sufficient current at low distortion, change to a different tube that also meets the requirements should have less effect on the sound. Of course, if you are driving a low impedance loads, long cables, etc., then switching from a higher impedance tube to a lower impedance set-up in the second position could well make an audible difference.

Sheldon

 

[jayme]

I built a 6SJ7/6922 Aikido. Sounded great!

Interesting. I assume you would need 2 6SJ7s per channel for the inputs. The only drawback I see to the separate bottles is that heater noise is not exactly the same, so is not cancelled as it would be in a single-bottle dual triode in the Aikido setup.

Also, was the 6SJ7 triode-strapped? And by "Sounded great!" I infer that you don't have it anymore...did you give it away or disassemble it?

 

[Burnedfingers]

A 6AU6/5687 also makes a very nice line stage. Only one 6au6 is used per channel.

My bad! I guess I should have read the "octal" in the subject.

 

[aletheian]

Interesting. I assume you would need 2 6SJ7s per channel for the inputs. The only drawback I see to the separate bottles is that heater noise is not exactly the same, so is not cancelled as it would be in a single-bottle dual triode in the Aikido setup.

Also, was the 6SJ7 triode-strapped? And by "Sounded great!" I infer that you don't have it anymore...did you give it away or disassemble it?

i just wanted to try an octal input pentode. I tried it in both pentode and triode strapped... after some tweaking, it was pretty dead quiet in either mode, but it took a little trial and error.

And Yes, I only breadboarded it... i didn't leave it together, and the tubes are now back in my collection.