[TenTec] Final Amplifier Class

[John Huggins]

Ken Brown wrote:

>John,
>
>The short answer is: It depends.
>
>Once upon a time it was standard procedure to run the final amplifier in 
>an AM transmitter in class C. This works fine when the final amplifier 
>is the stage that is modulated. A class B push pull modulator modulates 
>the class C final RF amplifier and it produces a good AM signal. This is 
>the way that most AM transmitters, both for broadcast and communications 
>used to work.
>  
>
Ah yes, that is what I forgot.  If you modulate the final stage it can 
be C, but if the modulation occurs earlier you need linear 
amplification.  Many thanks for jogging my memory on that simple truth.

>If an earlier low power stage is modulated, then all of the subsequent 
>RF amplifier stages need to be linear. They could be class A, class AB, 
>maybe even class B (probably not), but absolutely NOT class C. If the 
>rig runs SSB as well as AM, then it almost certainly generates the SSB 
>at a low level, and does not use a modulated final RF amplifier stage 
>even when it is in AM mode. In that case the final RF amp must be 
>linear, and is not class C.
>  
>
So in the case of external linear amplifiers for ham radio which are be 
name and definition linear amps can they be Class AB or B if they have 
only one output device (tube) or are they often big hot Class A?

In other words, can Class AB or B use just one tube or transistor (and a 
tank circuit) or must they always by a pair for push-pull operation to 
achieve the linear response?

>DE N6KB
>
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