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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