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Argus25 · 4th Jan 2019, 4:50 am

It is just another version of cascode. The difference simply occurs due to the point that the grid of the upper valve (or base or gate of a semiconductor) is connected.

In traditional cascode it is just clamped to a fixed voltage, but it can be connected to other points to, so as too add negative feedback and reduce distortion. In the case of the circuit posted, connecting the grid to the lower end of the cathode resistor (which happens to be connected to the plate of the lower valve) adds negative feedback to the upper tube(which is now a "degenerated current source').

The other place to connect the grid of the upper valve, is to ground, but for valves it is harder to meet the DC conditions, but with J-fets, it is perfect, which is how they built the Fetron.

4th Jan 2019, 4:50 am	#12
Argus25 No Longer a Member Join Date: Oct 2016 Location: Maroochydore, Queensland, Australia. Posts: 2,679	Re: Puzzling audio circuitry It is just another version of cascode. The difference simply occurs due to the point that the grid of the upper valve (or base or gate of a semiconductor) is connected. In traditional cascode it is just clamped to a fixed voltage, but it can be connected to other points to, so as too add negative feedback and reduce distortion. In the case of the circuit posted, connecting the grid to the lower end of the cathode resistor (which happens to be connected to the plate of the lower valve) adds negative feedback to the upper tube(which is now a "degenerated current source'). The other place to connect the grid of the upper valve, is to ground, but for valves it is harder to meet the DC conditions, but with J-fets, it is perfect, which is how they built the Fetron.