EF quote: RIt is well known that a grounded grid amplifier places a
varying load on its
driver stage.
NO ARGUMENT, here is Herzog's details: I have measured 10 ohms low to
35 ohms averaged over an rf cycle, and almost 1000 ohms at the other
peak. (4CX10000 tube).
It is recommended that the driver stage be heavily swamped to
avoid such load variations.
Herzog replies: YES this is the conventional wisdom. At one point we
used a 15 ohm series resistor, and 100 ohms shunt across the
cathode-grid; to get a 50 ohms for the vacuum tube with tuned circuits
driver, about 20 feet of coax away. but that wastes a lot of rf power,
and did not help or hurt the IMD.
A driver stage driving a 50 ohm dummy load and the final should be well
regulated. (I don't know what that means, but sounds good.)
By not having the driver swamped the varying load from the input of the
final amplifier can cause the driver IM performance to deteriorate.
Herzog agrees, BUT ....AH HA! but what counts is the overall, and in
some cases the driver is not used into the antenna directly, for lower
power, and is married to the final ampflier.
73
Gary K4FMX
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