48V Aikido linestage

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48V Aikido linestage

Postby EWBrown » Fri Mar 04, 2011 2:57 pm

John Broskie (www.tubecad.com) developed a low voltage Aikido board and circuit last summer. Of course, I can't resist playing around with some new / different circuit, so I went for one, before the Budgie was hatched.

Image

It all fits on a 5.4 X 3.6 inch PC board. This example is set up for ECC99s, with the cathode resistors 300 ohms, for 12BH7As, they should be 240 ohms, (though anything from 200 to 300 ohms will work)

This can be assembled in one of three variations, 24V using 6GM8s, and 48V, using either 12BH7As or ECC99s. The filaments of all four tubes are wired in series, so using 6DJ8s or 6N1Ps is not feasible, without some etch surgery which would be needed to isolate the hot end of teh filament string from the 48V B+ lines.

I decided to go with 12BH7As, mostly because I had them in sufficient quantity, and that the 48V, 380 mA SMPS I have on hand would not be overloaded (the ECC99 filaments each consume 400 mA @ 12VDC).
With the 12BH7As, the total plate curent is under 10 mA, closer to 8.5 mA total, depending on which tubes I stick into it. I'm finding that not all manufacturers' 12BH7As were created equal... :/

Right now, it is all out in the open, no chassis, proper shielded leads or stepped attenuators, so I am sure that it will do even better once it is properly set up and installed inside metal.

I suppose I could go for one of the 48V, 830 mA "Mean Well" SMPS from Jameco, for aboput $25. Then I'd have plenty of 48VDC available to supply the Aikido and a budgie or two - perhaps one for RIAA and a second one with the compensation network set up for NARTB tape head equalization.

And I suppose a third Budgie assembled as the 12B4A line stage could also be added, to go for the ultimate in flexibility. [:)

/ed B
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Postby Geek » Fri Mar 04, 2011 4:00 pm

Hmmm, I wonder what one of these w/trioded car battery pentodes would do?

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Postby burnedfingers » Sat Mar 05, 2011 3:56 pm

I have experience with Aikidos running higher plate voltages and have been very pleased with them. It will be interesting to hear how yours sounds with low voltage. I always thought that more voltage on the plate would make it sound better. I know that I could always tell a difference in a 6SN7 running it with higher voltage and just the right amount of current.
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I have a LV Aikido too

Postby Francois_G » Fri Mar 18, 2011 3:51 pm

I'm thinking of doing the necessary (minor) PC surgery to use 6.3 V tubes, primarily 6GU7. I believe it is identical to 12BH7 with 6.3V heaters. I have a bunch of very good RCA 6GU7s in stock and NOS 12BH7 and ECC99 are both a bit pricey.
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Postby EWBrown » Fri Mar 18, 2011 9:46 pm

THat should work. I was going to follow a similar scheme, by isolating the four tubes' filament connections and this would allow using a higher B+ voltage (use appropriately voltage rating caps)

But I liked the idea of an LV tube linestage, so I put it together as originally intended.

6GU7s are similar to 12BH7/A, and the "plinker" cheaper 8GU7s have the same operating characteristics as 6GU7, except for rhe filament voltage, so it would be an easy matter to use 8V, 16V or 32V for the filament supply.
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Re: 48V Aikido linestage

Postby Ludwig » Sat Jul 11, 2015 6:52 pm

Sorry to revive an old thread, but I noticed Broskie has finally updated his Low Voltage board to include two supply terminals, so one can now use separate B+ and H+.

http://www.tubecad.com/2015/04/blog0321.htm

I have about 10 pcs 6GM8 so thought this might be a nice board to build to compare to the 24v Budgie. However it's just an odd assortment of various branded tubes, is there a way of somehow matching them even though I don't have a tube tester? Or, does matching tubes not really matter in the aikido circuit?
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