[Elecraft] Final Amplifier Class

[John Huggins]

Thank you all for your help with the Amplifier Class questions.  I have 
found schematics and confirmed CBs use Class B in the final, the driver 
and sometimes earlier transistor circuits which ultimately feed a tank 
circuit before output to the antenna; It is clear the modulation happens 
way before it becomes 27MHz which makes good sense.

By the way this all came about because I was trying to make a point to 
the CB crowd about their radios being constructed with the barest 
minimum components to get the job done.  The CB finals I found handle 6 
watt average max (heat sinked of course) which I hope will dissuade 
folks from trying to tweak tens of watts continuous out of these poor 
radios.

As a bonus I learned more about how the various Elecraft products do 
their thing and for that I thank you all.

We can consider this thread closed.

Onward to a K2...

John Huggins wrote:

> Yes the handbooks are the place to go and I will sit with one tonight 
> to "reboot."  A splendid suggestion thanks.
>
> The information on what modern Ham Transceivers (like the K2 and K3) 
> do is also very handy.  Thanks for that too.
>
> John
>
> Gazdzinski, Brett J (Brett) wrote:
>
>> On AM, most CB sets, if not all, use class c in the final,
>> (single device), and collector modulate it with a push pull
>> class b modulator.
>>
>> Look up plate modulation, same thing but with tubes.
>>
>> You use class C on FM, and class ab1, ab2, or class b
>> on ssb.
>>
>>
>> Most modern ham rigs if not all use low level modulation
>> on AM, like ssb but with both sidebands and a carrier, and
>> amplify it like ssb, but with a much higher duty cycle.
>>
>> Class C can only be used with CW,  FM or plate/collector modulation
>> AM.
>>
>> SSB amplifiers (and AM amps) can be class B, AB1, or AB2, or A.
>>
>> Class A is VERY inefficient!
>>
>> All this stuff and more is in the  handbooks.
>>
>> Brett
>> N2DTS
>>
>>
>>
>>
>> Ladies and Gentlemen,
>>
>> I frequently contribute technical knowhow to a CB trucker's forum 
>> (before you press delete please read on).  The question came up 
>> concerning my assertion the single final transistor amplifier, 
>> typical in CB transmitter output circuits, operates as a Class A 
>> amplifier since the modulation required is AM and sometimes SSB, both 
>> being amplitude style modulations, and both desiring of good 
>> linearity in the amplification (at least I think so).
>>
>> I know for sure CB output circuits are not push pull since they have 
>> only one power amplifying transistor.
>>
>> Some are suggesting the less than 180° Class C amplification method 
>> is what CBs use.  I understand this requires a good tank circuit to 
>> complete the sine waves, but is supposedly inappropriate for 
>> amplitude style modulations like AM, DSB and SSB.  Various resources 
>> suggest Class C is fine for CW and FM.
>>
>> I am sure by now you are saying "That's interesting John, really, but 
>> what does this have to do with Elecraft?"
>>
>> Well, I suddenly remembered some advertisement for an HF Ham 
>> Transceiver that offered Class A mode in its output circuit for some 
>> improvement in some parameter.  Funny thing is I guess I thought Ham 
>> Transceivers always used either Class A with a single device or, 
>> perhaps, Class AB or B in a push-pull arrangement.
>>
>> What I need to know from Elecraft and/or any of you is:
>>
>> - What is the final amplifier class (A, AB, B or C) used in, say, the 
>> KX1, K2 or K3?
>> - Is it actually possible to use Class C with an amplitude modulation 
>> scheme like AM, DSB and/or SSB?
>> - Is the final amplifer in the KPA100 Class A?
>> - Do most Ham Transmitters utilize pairs of power devices in a Class 
>> AB or B in a push-pull arrangement?
>>
>> Hopefully this will fine tune my EE knowledge of circuits and make 
>> sure I have not missed something I should know so I can continue to 
>> represent the ham community well when offering advice to the other 
>> radio groups.
>>
>> Thanks for your help.
>>
>> John
>> KX4O
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