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Re: [Amps] Re: matching network

To: <>, <>," AMPS" <>
Subject: Re: [Amps] Re: matching network
From: R.Measures <>
Date: Wed, 28 Jan 2004 09:12:55 -0800
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>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 
**  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 
>to screen capacitances, almost double the input capacitance of a cathode 
>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 
>As always, "you pays your money and takes your choice"!
>73, Gerald/K5GW
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