Aikido/SMPS/SKA SS

[Dougie085]

I'm thinking about getting an Aikido linestage to use in front of 2 SKA GB150 modules. The amp section would be powered by a coldamp.com SPS30. My question is what kind of PSU would I need for the Aikido? I'll be using the Tongsol 6SN7 tubes. The SKA amp has ~30db of gain already as I remember so I don't need a ton of output from the Aikido. I will also be using Aikido's stepped attentuator for volume control. If anyone could help me out with some sort of PSU to use for the Aikido that would be great. The SMPS will be running +/- 40-42v so not sure if it could be used on that or what? Or if there is some other PSU I could buy to use on it.

[Dougie085]

Does anyone have any info on a PSU for a low voltage Aikido? Not sure if he outlines this in the instruction manual I emailed him but not sure when I'll get a reply.

[Boris_The_Blade]

They pretty much need at least 200 volts since two tubes are stacked in each section. I have just got a pair of mono boards and use 6SN7s and 6BL7s as outputs. It still has a lot of gain for my purposes about 10 v/v ~ 20dB), but i didn't want to use a power triode on the input because of heater current issues. As for the power supply, I'm using a series regulated source follower at 250VDC. It's pretty standard, but if you want a sketch i could have one up soon.

[Dougie085]

I thought I had read something on the tubecad site saying something about a low voltage Aikido. Maybe I was mistaken. Maybe I'll just do the Tube preamp in another chassis or something. A sketch of the PSU would be cool but would your PSU work good for using all 6SN7's? And why did you choose the tubes your using? Just curious as this is my first adventure into tubes.

[Boris_The_Blade]

I suppose it would be possible with the right tubes...I was looking into 6H30pi's at point but didn't go for it because they are pricey ($30 each). It may be possible with them...but that will be pretty much the only one.

Attached is my power supply.

edit: there is also a 470 grid resistor on the FET

I chose 6SN7 because I had some around and they are nice sounding tubes. I chose 6BL7 for low output impedance. See the tubecad pdf sheet for output impedances with different tubes and operating points.

[lousymusician]

Several folks have built low-voltage Aikidos with 6GM8's. The B+ is 24 volts, and they run the tube filaments in series from the same supply. Search here and at Tubecad for details.

[Boris_The_Blade]

Originally posted by Dougie085
would your PSU work good for using all 6SN7's?

yup i use 6SN7's in it now. Like lousymusician said there are options for low voltage aikidos but the 6SN7 won't work there...lookin at the curves at below 50V....it's hard to say if it would work (and sound ok)

[pmillett]

Originally posted by Boris_The_Blade

... but the 6SN7 won't work there...lookin at the curves at below 50V....it's hard to say if it would work (and sound ok)

Don't jump to conclusions based on published curves... they don't have enough detail at low voltages to really show anything:

http://members.aol.com/sbench102/TubeMisc/6sn7lv.gif

Looks pretty linear above 12V.

Also, keep in mind the datasheet curves were drawn by guys (I imagine wearing white shirts with black ties) sitting at a drafting board, not by a computer.

I've used ECC88/6922/6DJ8 types down to 12 volts or so on the plate with good results. They are very, very similar to ECC86/6GM8's (actually they look identical outside, though I'm sure there are internal differences). They should work great with +/-42V, even as an SRPP.

Actually, that transmitting tube you see in my avatar is running on +/-24V. but that's another story

Pete

[ssanmor]

If this is of some help, some of our customers used our coldamp SPS80 switching PSU to generate the high voltage needed for their tube amps or preamps. I recall he used two SPS80 in series to get 240V or so.
You can also use a SPS30 to get 120V volts or so, or order a special version for lower voltages.

If you need something special, please ask us at info@coldamp.com

[Shoog]

Woodturner Fran has just built an Aikido with the ECC86 and a 24V rail. He is more than happy with the result and I trust his opinion. He has a very good overall system and he noticed a significant improvement over his Tubecad passive preamp.

There is a lot of prejudice against this type of implementation and this valve - but usually from people who haven't built with them. I wouldn't try it with the ECC88 which i think is happiest with at least 80V.

Shoog