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Re: [Amps] Old Moto RF Decks

Subject: Re: [Amps] Old Moto RF Decks
From: Manfred Mornhinweg <>
Date: Thu, 04 Dec 2014 13:25:50 +0000
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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!


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.


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