Carl,
SS QRO development has been slow and commercial user requirements have
driven it, HF is a small market these days and the money is at VHF and up.
And there is more money in medical equipment, than in radio transmitters of any
kind.
Ive no problem with 12-15dB gain when 100-200W of drive is available, just
think of it as GG SS (-;
Funny, I look at those things from the other side! When I see a GG amplifier, I
think of it as a very nonlinear active device used in a circuit that has very
large negative feedback!
Ron,
I agree with the need for feedback, but the operating mode with the
best overall efficiency which is suitable for all modulation modes
without switching is class "B" push pull operation...
I have always considered class "AB" to be class "A" just without the
linearity.
Maybe we need to reach some kind of agreement on what exactly is meant by class
B and class AB. Because class AB in tubes an in transistors tends to run at very
different idle currents! Tetrode amplifiers I have seen typically have an idling
current of 20 to 40% of the maximum current. Solid state class AB amplifiers
instead run with a much lower idling current, such as 2% of the maximum. In that
way, a class AB solid state amplifier is far closer to class B than class A,
while a tetrode class AB amplifier is indeed class A over much of the dynamic range.
Maybe when you think of class B solid state amps, you include a small idle
current? If so, then it's fine, although that kind of operation, by the old
definition is class AB.
Some idling current is needed in any such linear amplifier, because the transfer
curve of the active devices has a strong bend at its start. A pure, exact,
precise class B solid state amplifier, meaning that each device conducts exactly
for one half RF cycle, would have severe crossover distortion.
Personally I would like to call an amplifier class B, even if it has a small
idling current, and so each device conducts over slightly more than half a
cycle. After all, the idling current can tend toward zero, as the devices get
better! But I understand that the valid definition is still by conduction angle,
and by that definition a class B amplifier must have zero idling current.
Manfred
========================
Visit my hobby homepage!
http://ludens.cl
========================
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|