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.
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