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RE: Other Methods IT

You said "Current into the Miller capacitance" but then you said "No power is delivered to the load"

If the driver stage has to deliver current to the Miller capacitance then isn't the Miller capacitance a load for the driver tube?

Maybe I'm not understanding what you mean by "the load" or maybe I don't understand what you mean by "consume power".


by Thorsten Loesch

"In addition, a directly heated triode (and any similar triode) has a quite substantial Input Capacitance comprising mostly the miller amplified Anode to Grid Capacitance.

The input Capacitance of a given Valve is (Cga + Cstray) * Mu + Cgk. This capacitance must be driven from somewhere, not only with respect to the frequency response, but also concerning the current draw at higher frequencies.

For a 300B Valve the input capacitance is usually around 70pF, a little more in reality due to stray capacitance's from the wiring or pcb. If we take 80pF Input Capacitance and a Bias of 70V for our above mentioned operating point we must be able to supply the current drawn by this capacitance up to at least 100kHz (usually a much higher frequency is strongly advisable) at full voltage swing.

The impedance of the 80pF Capacitance at 100kHz is around 20kOhm, the peak current drawn by this capacitance at full signal is 3.5mA."




70v times 3.5ma of current is .245 watts of power that needs to be sourced from the driver stage to satisfy the Miller.

I refer to that, rightly or wrongly, as the driver stage delivering power.

and my point was, regardless of the type of coupling the Miller capacitance current requirement still needs to be satisfied.


Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"


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