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In Reply to: RE: Class A push-pull posted by Triode_Kingdom on December 7, 2024 at 16:04:17:
I've been refurbishing an Electro Voice A-20 amplifier, which uses a pair of 6V6s in class B and makes 20-25 Watts. It has a unique driver circuit which keeps the output tubes operating at the right point (so no bias or balance controls). The output transformer is conventional but its in the cathode circuit of the output tubes and the output section is wired as a Circlotron. The Circlotron operation prevents the usual spike that would otherwise occur when the tubes go into cutoff, so no distortion at low power levels. It has excellent bandwidth.
In addition there is a feedback control which is a 2-deck device, allowing you to balance between full Voltage feedback (so the amp can behave as a Voltage source) or full current feedback, allowing it to act as a current source. For speakers like we see often driven by SETs, you set the damping control to noon, as which point its a power source (similar output impedance to an SET, but with equal amounts of current and Voltage feedback).
BTW if you google the schematic, Electro Voice published it with an error. The screen resistor also serves as the plate resistor for the driver tube. The schematic shows something else.
At any rate, 6V6s are much easier to drive than 6L6s or any of the Kinkless Tetrodes. In proper UL mode or in Circlotron mode as described above this might make for an amp that could suit the bill.
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Follow Ups
- RE: Class A push-pull- something to consider - Ralph 11:57:04 12/13/24 (5)
- RE: Class A push-pull- something to consider - PakProtector 03:24:29 12/17/24 (3)
- If you can find a copy of the schematic - Ralph 08:49:29 12/17/24 (2)
- PDF Schematic - Triode_Kingdom 09:18:55 12/25/24 (1)
- Yes- that might be the advantage of a Circlotron - Ralph 08:58:47 12/26/24 (0)
- RE: Class A push-pull- something to consider - Triode_Kingdom 11:00:59 12/14/24 (0)
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