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Argus25 · 4th Jan 2019, 10:48 pm

I think the main issue was that the favorable attributes of the triode, especially noise consideration as noted above, could not be harnessed in RF circuitry because of the lack of isolation between the input and output due to the grid-plate Miller capacitance.

Clamping the triode plate to a fixed potential (although looking into the cathode of a cathode follower has about a 300 Ohm impedance with signal valves) allowing the plate current of the lower valve to simply pass via the upper valve, solved this problem and made the arrangement in that respect as good as a screen grid pentode, but with the noise benefits of the Triode.

It means that if required you can have tuned circuits of the same frequency in the grid & plate circuits of cascode, and they don't exchange energy with each other and don't normally require neutralization.

4th Jan 2019, 10:48 pm	#25
Argus25 No Longer a Member Join Date: Oct 2016 Location: Maroochydore, Queensland, Australia. Posts: 2,679	Re: Puzzling audio circuitry I think the main issue was that the favorable attributes of the triode, especially noise consideration as noted above, could not be harnessed in RF circuitry because of the lack of isolation between the input and output due to the grid-plate Miller capacitance. Clamping the triode plate to a fixed potential (although looking into the cathode of a cathode follower has about a 300 Ohm impedance with signal valves) allowing the plate current of the lower valve to simply pass via the upper valve, solved this problem and made the arrangement in that respect as good as a screen grid pentode, but with the noise benefits of the Triode. It means that if required you can have tuned circuits of the same frequency in the grid & plate circuits of cascode, and they don't exchange energy with each other and don't normally require neutralization.