Hello:
I'm interested in contacting someone on this list that is very familiar with
the Constant Current curves and the calculations required to determine the
operating parameters for an RF amplifier.
I'm trying to design a conventional Doherty using either two 4-400A or two
6146A tubes. I have searched for Doherty parameters on data sheets and I have
been doing the parameter derivation for a Continental Electronics 316F 10 kW
transmitter. The 316F derivations, the Doherty parameters I found for the 5682
triode and 8974 tetrode all have one thing in common. And that is, the RF drive
for the carrier tube for 100% modulation is 1.5 times the RF drive for carrier
only. I would think this figure should be 2 and not 1.5.
I have been driving myself absolutely bonkers trying to figure this out, and
I can't. The original Doherty patent says that the grid drive on the carrier
tube has to go up by about 30% during the peak positive modulation crest to
maintain saturation. If I drive the tube harder and recalculate a new operating
line, the plate swing increases and the RF plate current goes up, so the stupid
tube cannot be in saturation then. The biggest problem I'm having is how to
represent tube operation when in saturation with an Operating Line drawn on the
Constant Current Curves
So I need to communicate with someone that is very familiar with these
calculations using the CC curves and how that relates to the Doherty design
calculations. I should mention that the 316F 10 kW transmitter is _never_
driven into
grid current during carrier only or 100% peak positive modulation crest, so
the 90 degree grid network is seeing a constant impedance under carrier only
and
100% crest conditions.
I really need some help with this. Any of you done calculations like this
before? BTW, I have my heart dead set on building a Doherty. I have not yet
decided if it will be built for 160 or 80 meters.
Jeff Glass, BSEE CSRE
WB9ETG since 1970
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