[Amps] Old Moto RF Decks

[Manfred Mornhinweg]

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

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