>> --------- Forwarded message ----------
>: From: Rich <2@vc.net>
>> To: <bearlabs@netzero.net>, "AMPS"
>>The grid current that flows is so insignificant that no
>> appreciable current *can* flow, so the tube does
>> not reach beyond AB1 in practical terms.
>
>: ** Eimac rates the maximum permissible grid bias PS
>>: source resistance for its tetrodes and pentodes. This
>: determines how much grid-current can flow. In my
>: experiences with AB1, there is a tradeoff in IMD when grid
>: current flows -- i.e., the amplifier is driven into AB2.
>
Skipp: Non-standard attribution (:) marks do not work as well as (>).
-
>In his audio amplifier examples, the "grid circuit" is
>very often a much higher designed input Z.
>-
True, but this discussion group is about RF amplifiers.
>: The argument that high resistance is used to prevent
>: loading down the drive voltage does not hold water
>: because, in RF service, the typical grid-terminating
>: resistance is 50-ohms (or 200-ohms through a 1:4
>: transformer) in order to present a 50-ohm termination
>: for the radio.
>-
RR
>If he wrote that, then he is a little off base... like RF amps,
>there are rules and guide lines for the amplifiers he
>described in his examples.
Like unto wearing football shoes to play a basketball game.
>The grid resistors are
>chosen for operation with the phase inverter circuit
>layout delivering drive voltage to the push pull output
>stage. The resistors are chosen as loads for the
>phase inverter, the driving voltage developed across..
>-
>>In practice the output signal is merely clipped when
>>it reaches the point where in an AB2 amp grid
>> current would start to flow.
>-
>I would prefer sage flat topping or hard limiting as a
>more descriptive "better label". I'm sure the stage
>is into compression/hard limiting/flat topping or
>what every label you want to use long before AB2
>comes to the table.
>-
>: ** Would ? The reality is that some grid current Does
>: flow and IMD increases.
>-
>Big time increase...
>
Good for clearing a chunk of the band and keeping the competition at bay.
>>web I am sure. Guaranteed this amp will not run into
>>AB2 no matter how much
>>signal you put in the front end... : -)
>>
>: ** I can not believe that no grid current will flow when
>: the amplifier is over driven.
>-
>It does... in both his and your examples.
>-
Another amplifier "expert" ?
- Rich..., 805.386.3734, www.vcnet.com/measures.
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