Could it be that adding a diode + resistor to a JFET across gate make it have automatic gain control for many Megohms Rg or simulating electron tube instant clipping behavior with few MOhms Rg?
The rectificating grid action of the electron tube at large signals increases negative bias, therefore decreasing current, therefore Gm, therefore gain. Vary Gm tubes with deliberate uneven grid must be doing the job even better.
This was first shown to me when I disconnected the capsule from a U47 and applied a signal from a sine generator with 10Db steps. When a large signal was suddenly reduced by 10db gain was increasing by a time constant (coming back to its normal value after automatic gain reduction!), output of VF14 electron tube was an undistorted sinewave all the time.
The rectificating grid action of the electron tube at large signals increases negative bias, therefore decreasing current, therefore Gm, therefore gain. Vary Gm tubes with deliberate uneven grid must be doing the job even better.
This was first shown to me when I disconnected the capsule from a U47 and applied a signal from a sine generator with 10Db steps. When a large signal was suddenly reduced by 10db gain was increasing by a time constant (coming back to its normal value after automatic gain reduction!), output of VF14 electron tube was an undistorted sinewave all the time.
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