[ARC5] AM linear amplification

[Richard Knoppow]

    I have Barton's paper. However, Class-B linear amplifiers for RF had 
been in use for some time before he came up with high level modulation. 
Of course, the same thing applies to Class-C amplifiers. They put out 
essentially pulses which are integrated into complete RF waves by the 
tank circuit. Class-C is capable of very high efficiency depending on 
the pulse duration.  However, increasing that requires very high bias 
and very high driving voltage so mostly a compromise was found for an 
efficiency of perhaps 70%. A modern CW transmitter would be capable of 
much greater than this.
    Also, FWIW, I have had little success in finding out when different 
"classes" of amplifiers originated. Certainly Barton did not invent push 
pull or Class-B but does seem to have been the first to apply a high 
efficiency, high power audio amplifier to act as a modulator directly 
feeding the plate of a high efficiency RF amplifier.
    I mentioned the high efficiency linear amplifier invented by William 
Dohrty in my other post to this list and its later embodiment by 
Continental Electronics. This type of transmitter and also the pulse 
modulated transmitters made by Gates and later Harris became very 
popular with the rise of Top-40 stations. Most of them used very heavy 
processing to sound LOUD, so much that often the modulation transformers 
of plate modulated transmitters were either burned out or began to arc. 
Sometimes the modulation transformer had to be isolated on insulators. 
Since there is no transformer in either the Doherty or Gates system they 
were immune from this problem.
    This is all so far removed from ARC-5 gear that I think I had better 
stop.

On 12/19/2016 2:32 PM, Jim Haynes wrote:
> I'll insert a bit of lore from Loy Barton, who invented the use of a
> class-B push pull modulator transformer coupled to the RF amplifier
> plate as a way to do AM.  (Replaced the much less efficient Heising
> modulation)
>
> He noted that it may be convenient to generate AM at a lower power level
> and then amplify it in a linear amplifier.  And pointed out that it is
> sufficient for the "linear" RF amplifier to be Class B, because the
> tank circuit will turn the half-sinewave pulses into sine waves.  It
> is only necessary for the output amplitude to be proportional to the
> input.  Which precludes a Class C amplifier but is satisfied by Class B.
>
> Loy E. Barton, "Recent Developments of the Class B Audio- and
> Radio-Frequency Amplifiers" Proceedings of the I.R.E., July 1936,
> vol 24, no 7, p. 985.
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-- 
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL