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Re: [Amps] Re: matching network

 To: , ," AMPS" Re: [Amps] Re: matching network R.Measures Wed, 28 Jan 2004 09:12:55 -0800
 ``` >A cathode driven configuration doesn't inherently cause excessive grid >current. If proper grid and screen voltages are supplied, the grid current >is a function of grid bias voltage and drive level, just as in grid driven design. > ** The thing that makes tetrode RF grounded-grid different from tetrode grid-driven is that in grid-driven, the RF driving signal exists between the RF-grounded screen and the control grid. However, in grounded-grid configuration, there is Zero signal V between the grid and the screen - g1/g2 amplification is zero. Also, in grid-driven config., there is zero current and a moderate amount of screen current The reason is that the grid operates in the negative region - which does not attract electrons, however, the screen is positive, which does attract electrons.. ----- > The higher the drive level, the higher the peak cathode voltage, the higher >the peak grid voltage, the higher the peak grid current and the higher the >average grid current (which is what we are measuring). > >The cathode driven configuration also offers the same negative feedback >benefits as in a triode cathode griven (grounded grid) circuit, primarily a >reduction in odd order products. > >One of the main reasons grid drive circuits are not popular for vhf/uhf >amplifiers is because the input capacitance is the sum of grid to cathode and grid >to screen capacitances, almost double the input capacitance of a cathode drive >circuit consisting of cathode to grid capacitance only. ** good point The trade-off is difficulty in obtaining wide freq. coverage with g-g. >The circulatng >currents are higher and resulting I^2 X R losses are higher in the input >matching network. > >At h.f. these effects are minimal and either configuration works fine. The >bulky grid termination resistor can be eliminated with the cathode drive >configuration. > >As always, "you pays your money and takes your choice"! > >73, Gerald/K5GW _______________________________________________ Amps mailing list Amps@contesting.com http://lists.contesting.com/mailman/listinfo/amps ```
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