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By calling it the Aikido, I am borrowing the name of the driver circuit as created by John Broskie at Tube Cad. You can view his work here.
What we have is John's Aikido style amplifier implemented using a 5965 as the SRPP stage, and a 5687 at the triode loaded follower driving the 2A3 grid. Both tubes in the input circuit are running in high current mode. The Aikido's strengths are virtually no power supply noise at the grid of the 2A3 and extreme linearity. By using the Aikido style as a driver, I am able to tap the high voltage power supply at a higher point providing more linearity in this stage. The result is a low noise 2A3 amp that actually sounds like a 2A3 and is virtually uncolored by the driver/input stage(s).
Yellow! By request of buyer.
Any future amps will be black and silver only.
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Shown below is a point to point board with the Aikido circuitry mounted. Actually, what you are looking at is the anti-noise injection circuit and a few resistors to safety the circuit as suggested by John. None of the audio passes through this board. The input is direct coupled to the SRPP input stage, which is then direct coupled to the loaded follower stage which in turn is capacitively coupled to the 2A3 grid. The true signal path is kept as direct as possible for this layout. Silver in the solder and silver plated wire are used in the signal path except for actual component leads. This includes the Transcendar USA made output transformers which use silver/teflon.
The audio leaves the input tube via the green wire
and is directly coupled to the follower grid via the 1K2 resistor.
The trim pot sets the noise injection and is a set-once-and-forget control.
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Picture below showing the interior. The chassis is .080 clear-anodized aluminum. Quite heavy. The interior frame provides additional strength (all those trannys are heavy!) and also provides shielding of the power supply from the rest of the unit. Overall size of the top deck without panels and not counting the connectors is 15"W x 12"D x 2.5" high.
You can see the 2A3 hum balance pots and the 2A3 filament trannys.
The hum pots are industrial grade.
The vintage Hammond power tranny with cloth leads just loafs along in this circuit.
Ample reserve.
Four and eight ohm outputs are provided.
jef
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