I've built a few Aikidos.
The 12VAC setup for 12AU7s and a 18VAC power xformer:
The Octal Aikido w/ SS power supply:
and the dual mono octal Aikido with Janus PS:
I don't have any of them anymore (gave to friends) but my imperfect memory remembers the 12VAC as my favourite. Had a certain amount of liveliness to it the octal ones didn't.
But, best advice I have is build all the ones you can get your hands on and find out for yourself. No idea when John will run out of/refill stock. Get 'em while they're hot.
The 12VAC setup for 12AU7s and a 18VAC power xformer:
The Octal Aikido w/ SS power supply:
and the dual mono octal Aikido with Janus PS:
I don't have any of them anymore (gave to friends) but my imperfect memory remembers the 12VAC as my favourite. Had a certain amount of liveliness to it the octal ones didn't.
But, best advice I have is build all the ones you can get your hands on and find out for yourself. No idea when John will run out of/refill stock. Get 'em while they're hot.
The Aikido manual does state on page 15 that
".... a 12AX7 input tube will yield a gain close to 50 (mu/2) whic would be suitable for an SE amplifier's input stage,"
I'm going to swap the 12AT712AU7 for 6N1Ps (with heaters in series) and possibly increase the HT from 210 to 250v.
6N1P will give you a voltage gain of about 15-16x. But the anode current is much higher than the 12AX7, and the heating current is twice as high, about 600mA. Otherwise, the 6N1P sound nice and are not expensive. I picked up a matched quad on ebay and have been very happy with them. For Aikido both halves of the tube should be paired.
Thank you. I have instead bought a set of matched 6N2P-EV which have hgher gain. (like a 12AX7 but with 6.3v heaters)
Yes they are similar to 12AX7, just a different pinout. They say it sounds great, I haven't tried it.
Chinese 6N4 or 6N4-J is a pin-compatible replacement for the 12AX7, but I don't know anyone who uses those tubes.
Chinese 6N4 or 6N4-J is a pin-compatible replacement for the 12AX7, but I don't know anyone who uses those tubes.
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With 12AT7 input and 12AU7 outout tubes, I see 1v in for 19v out into 15k for 0.2% 2H and 0.69% 3H so i will see if the 6N2P improves or not.
Aikido as EL34 driver stage - good results using PCC88 for the input tube (R3,4 = 220r) and ECC82 (R6,7 560r) for the output.
Spent hours roling tubes and changing the cathod resistors as required but had the best results by far with the above combination.
Gain is about 13x and I was looking for 12-15v RMS with lowest distortion running them at 218v (no R12s fitted)
The results are v.good, with 2nd being the predominant harmonic and still well below 1% even at 19v RMS out (into 540k, at 1kHz)
Spent hours roling tubes and changing the cathod resistors as required but had the best results by far with the above combination.
Gain is about 13x and I was looking for 12-15v RMS with lowest distortion running them at 218v (no R12s fitted)
The results are v.good, with 2nd being the predominant harmonic and still well below 1% even at 19v RMS out (into 540k, at 1kHz)
