Common Emitter Amplifier Questions

[Roly]

Admittedly, I used to be in the tubes good, transistors bad camp

They are all just electronic components to me, part of a pallette that nowadays stretches from small signal diodes to entire sub-systems like GPS receivers and systems like the Arduino.

I guess that would be called Drain following, but I think you just coined the term.  The trick is to avoid it (unless you are looking for frequency doubling in a fuzzbox), don't overdrive the stage, use clipping diodes across the signal path to make such overload impossible, design for bags of headroom.

Careful putting resistors in series with the gate - 500k strikes me as too much.  Like a triode these suffer from Miller effect when the tiny stray feedback cap between Drain and Gate is multiplied and can cause an unwanted HF Pole and premature HF rolloff.

[Enzo]

Not my area of expertise, but it looked to me like your JFET had an unbiased gate on the drawings and scope shots.  I see Roly has added bias to the gate in his drawing.

[sa230e]

I thought it was the source resistor that sets the bias on a JFET.

[Roly]

It does - vis a vis the voltage on the Gate.  If we run an MPF102 (coz it's common worldwide) and we simply ground the gate via, say, a 1Meg resistor, then a current of about a mA results in a stage with too little headroom to input overload, your input diode clipping.

By elevating the Gate we can now have our DC cake and AC eat it too.