[Amps] Amplifier classes in solid state

[jeff millar]

Interesting question. The original definitions certainly have tube 
origins. But the classes also map into conduction angle and linearity 
effects...which applies to all amplifiers. Setting aside the definitions 
related to tube grid current...

    * Tubes only draw grid current when voltage positive vs the cathode
    * Some tubes need positive grid voltage to get full plate current
      swing, some don't
    * All bipolar transistors draw base current proportional to drive
    * All FETs have virtually no DC current

My opinion...

    * Class A: applies to both,
          o 100 % conduction through RF cycle
          o constant current
          o linear operation
    * ClassAB: some similarities
          o between 50 and 100% conduction
          o forget the AB1, AB2 distinction for solid state
          o supply current rises with drive
          o some idling current
          o reasonably linear operation
    * Class B: some similiarities
          o 50% conduction angle
          o supply current rises with drive
          o Biased exactly at cutoff
          o still sorta linear operation
    * Class C: applies to both
          o less than 50% conduction
          o supply current rises with drive
          o Biased beyond cutoff
          o very non linear operation

jeff, wa1hco

Will Matney wrote:

>Hey all,
>
>I gotta ask this question;
>
>Is the amplifier classes A, AB1, AB2, B, and C valid for solid state devices?
>
>Now my training says it is as the base of a semiconductor is the same as the grid on a triode. There's the part about grid current flowing, but of course we have base current flowing when running class AB1 or A as the base is biased on with a regulator. To me, I cant see any difference in the action of a triode or a transistor if the transistor is biased correctly.
>
>Now, most know I'm a tube head instead of solid state when it comes to RF amps. Am I missing the boat here and just dont see something?
>
>All comments welcome,
>
>Will
>
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