On Sat, 28 Aug 2004 19:20:06 +0100, John Woodgate
wrote:

Oh, thank you, Paul. Remind me to invite you to explain something one
day.

People are using 'linear' in two different senses.

No kidding? Only two? ;-)

For audio, in fact
for any amplifying stage with an **untuned load**, linearity requires
linearity of output current with respect to input voltage, (Class A
single ended or push-pull, Class B push-pull).

But with a **tuned load**, 'linearity' can be achieved even with Class C
biasing. This is why linearity in this case is defined as output power
being proportional to input power.

Okay. I'm quite happy with that. Any not?
--

"What is now proved was once only imagin'd." - William Blake, 1793.

But with a **tuned load**, 'linearity' can be achieved even with Class C
biasing. This is why linearity in this case is defined as output power
being proportional to input power.

Okay. I'm quite happy with that. Any not?
--

I am not. For a normal ham amp to be linear it can not be biased class C.
Class C will not reproduce a SSB or AM signal. It only works with constant
signal levesl such as FM or CW. The tunes circuit "rings" and reproduces
the missing portion of the sine wave of a single frequency. It can not do
this for signasl where the amplitude is constantly changing such as SSB or
AM.
As a circuit is baised from A to B to C portions of the waveform is clipped
out. Class B can be used for audio or rf if it is in a push pull circuit
so that as one device (tube or transistor) is cut off the other is
conducting on the other portion of the cycle.

The term linear is now being used incorrectly for almost any RF amp even if
the amp is biased class C. While it is not linear many use the term linear
when the word amplifier or class B or C ampifier should be used.

Any class ( A, B , C ) of amp can be plate modulated for AM. It is then
not really an amplifier.

In article . net,
Ralph Mowery wrote:
[...]
Any class ( A, B , C ) of amp can be plate modulated for AM. It is then
not really an amplifier.

I disagree with this. If the stage puts out more RF than it takes in, it
is an amplifier even if the purpose of the stage is to be a modulator.


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--
forging knowledge

On Sun, 29 Aug 2004 00:48:51 +0000 (UTC),
(Ken Smith) wrote:

In article . net,
Ralph Mowery wrote:
[...]
Any class ( A, B , C ) of amp can be plate modulated for AM. It is then
not really an amplifier.

I disagree with this. If the stage puts out more RF than it takes in, it
is an amplifier

By that definition, it could also be an oscillator!
--

"What is now proved was once only imagin'd." - William Blake, 1793.

In article ,
Paul Burridge wrote:
On Sun, 29 Aug 2004 00:48:51 +0000 (UTC),
(Ken Smith) wrote:

In article . net,
Ralph Mowery wrote:
[...]
Any class ( A, B , C ) of amp can be plate modulated for AM. It is then
not really an amplifier.

I disagree with this. If the stage puts out more RF than it takes in, it
is an amplifier

By that definition, it could also be an oscillator!

If you are putting RF in and getting RF out at the same frequency, in any
reasonable case the circuit is acting as an amplifier. The circuit may
well oscillate when no input is applied. This sort of amplifier was very
common in the past and still is somewhat common.

A super-regen receiver is the most obvious example. Many tube based FM
receiver designs had a FM detector that would oscillate with no input
signal. The "burst lock oscillator" in a TV is in fact a very narrow pass
filter and amplifier when there is a burst to lock to. With no burst it
oscillates.


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forging knowledge