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 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. 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
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