Triode emulator - from a pentode to a triode

[tca]

Hi again,
as you all know most of us have a few obsessions... my latest one concerns what the title implies: Triode emulator - from a penthode to a triode.

In 1938 Schade proposed a mechanism to transform a pentode tube into a triode by connecting the plate to the grid using a resistor network. Here is the graphs from
is work "Beam Power tubes" by O. H. Schade, March 1938.



So I've simulated a few circuits to try to understand a bit more what is going on. All of you know the triodizer. Here are the simulations. The version described in the text with a battery at the gate:



and the circuit from a MIT lab course



Wonderful graphs don't you think!

I've also simulated the Fetzer valve circuit and as suspected the characteristic curves are not of that type... although it sounds good



This graphs and simulations does put things into perspective.

I'm going to breadboard some circuits and report later.

Comments/variations on the circuits?

Cheers.

[amptramp]

You can get away with getting DC response close to a triode from a FET but you should be aware of the large interelectrode capacitances that vary with voltage and their effect on AC response.  Good emulation may require a cascode connection to mitigate Miller (drain-to-gate) capacitance and low output resistance to limit the effect of output capacitance variation with voltage.  Tube capacitances are very low and do not vary much with voltage.  FET capacitances are large enough to be a concern in the audio band.  High drain voltages help with the output capacitance.  Low drive impedance helps with the input capacitance.