Re: Doubling

On Nov 21, 9:30 pm, exray <radioex...@xxxxxxxxxxxx> wrote:
This is a really dumb question but it dawned on me that I did not know
the correct answer.

In terms of old transmitters from the 20s/30s...In a crystal oscillator
  I understand the concept of setting the oscillator output tank to
favor the harmonic from the crystal.  (Stop me if I'm wrong already...)

You're right on the trail. Most oscillator circuits are operating deep
in class C. The exceptions are called "marginal, doesn't always start"
oscillators :-).

Some oscillators make the crystal operate on an overtone. An overtone
is often very very close to a harmonic. In this case the LC tank
chooses the overtone where gain is going to be greater than one.
Overtones close to odd harmonics are usually much more active in the
crystal.

Other oscillators make the crystal operate on the fundamental, and the
output picks off the harmonic. This is where the electron coupled
oscillator shines.

It's possible to have the crystal operate on the overtone, and then
electron-couple to pick a harmonic of the overtone. You see this in
some 40's/50's/60's era VHF projects.

But in a doubling amplifier stage am I counting on having enough
harmonic content at the input or am I creating the harmonic with the
non-linearity of the amplifier?

Mostly creating. It doesn't hurt if there's some harmonic content at
the input. Again, for efficiency most of the power stages will be in
class C already, and if they need to multiply in a non-power stage
they'll set it up to make a lot of harmonics.

Individual stages are sometimes configured in push-pull to favor odd
harmonics over even ones, or are biased to be favorable for the
desired harmonic.

Tim.
.

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  • Re: Doubling
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    ... In terms of old transmitters from the 20s/30s...In a crystal oscillator ... I understand the concept of setting the oscillator output tank to ... If the energy extracted from the oscillator is at twice the crystal frequency it's because of harmonics generated in the tube. ... One description I read of the tritet osc described it as being an oscillator with inherent class c amplification, hence the plate circuit being tuned to the desired 'harmonic' and the crystal is indeed operating at its fundamental freq. ...
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