> --------- 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.
-
In his audio amplifier examples, the "grid circuit" is
very often a much higher designed input Z.
-
: 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.
-
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. 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...
>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.
-
cheers
skipp
________________________________________________________________
Sign Up for Juno Platinum Internet Access Today
Only $9.95 per month!
Visit www.juno.com
|