On Dec 14, 10:27*pm, "NoSPAM" wrote:
*Actually you do not need any nonlinearity to make a doubler
(quadrupler, etc.).

You mean to tell me that you take a clean sine wave... pass it
through... say a single-ended class A amp... and you can put a tank on
the output of that amplifier... and tune for a harmonic? You will get
nothing.

"Telstar Electronics" wrote in message
...
You mean to tell me that you take a clean sine wave... pass it
through... say a single-ended class A amp... and you can put a tank on
the output of that amplifier... and tune for a harmonic? You will get
nothing.

Class A means that plate current is flowing throughout the entire cycle of
the input wave with the tube operated between cutoff and saturation. It
says nothing about the linearity of the tube's transconductance (plate
current as a function of grid voltage). With real devices, the
transconductance curve is ALWAYS nonlinear to some degree, producing
distortion (and harmonics). As you decrease the drive to a single-ended
Class A amplifier, you are working on a smaller and smaller portion portion
of the transconductance curve which decreases distortion. In the limit
where only an infinitesimal part of the transconductance curve is used, you
will get no distortion and no harmonics. Of course, in this situation the
tube produces NO output.while drawing current from the power supply.

The scheme that I was talking about, known as a push-push doubler,
generally uses the tubes operated in Class B although AB operation will
work too, but it produces less harmonics. The real advantage of a
push-push doubler is that odd order harmonics and the fundamental cancel
out, making the resultant waveform easier to filter.

73, Barry WA4VZQ

On Mon, 15 Dec 2008, Telstar Electronics wrote:

Date: Mon, 15 Dec 2008 06:16:29 -0800 (PST)
From: Telstar Electronics
Newsgroups: rec.radio.amateur.homebrew
Subject: Doubling

On Dec 14, 10:27*pm, "NoSPAM" wrote:
*Actually you do not need any nonlinearity to make a doubler
(quadrupler, etc.).

You mean to tell me that you take a clean sine wave...

You might want to consider qualifying your thinking on this by setting a
specification for harmonic distortion (in other words, you might need to
consider how much of that "clean sine wave" signal has other components
in it, including non-harmonic componentes)

pass it
through... say a single-ended class A amp...

You might also want to consider, here, too, how much harmonic distortion
THAT class A amplifier also causes which makes a contribution to the
output.

and you can put a tank on
the output of that amplifier... and tune for a harmonic? You will get
nothing.

You might even more also want to consider that any tuned circuit will pass
energy not at the resonance of that tuned circuit.

You would probably contribute to your own enlightenment if you actually
did some real experiments on this. It does not take long to do.

Back when I was an undergraduate student with major in physics (BS, 1966),
I worked in a Mossbauer Effect spectrometer lab and we built most of our
equipment (dual delay line pulse amplifiers, regulated DC power supplies,
repairing survey meters, etc) my boss had me build a waveform converter
that used a network of resistors and diodss to convert a sawtooth waveform
to sine wave and he was doing this because the book he got the circuit
from said that there would be less than 1% harmonic distortion and he was
interested in that specification for the spectrometer drives and all of
our commercial high quality signal generators were worse in that
specification, particulary at the very low frequencies we ran the drives
at (less than one cycle per second).

So, you have to define what you mean by "clean sine wave." But, I'll also
say that, no, you will not get nothing if you tune to the second harmonic
and have a linear amplifier (unless, maybe, you have a _perfect_ sine wave
and a _perfect_ linear amplifier [the rest of you guys might want to comment
on this yeah, I know about Fourier analysis, too]).

"Telstar Electronics" wrote in message
...

You mean to tell me that you take a clean sine wave... pass it
through... say a single-ended class A amp... and you can put a tank on
the output of that amplifier... and tune for a harmonic? You will get
nothing.

Of course you will. No active device is perfect.

I decided to illustrate the fact that a single ended triode operated in
Class A can produce harmonics. For a tube, I used a 6C4 (1/2 of a 12AU7)
operated with 300 volts on the plate, a grid bias voltage of -7 volts,
driven with a pure sine wave of 14 volts peak-to-peak. The high driving
voltage was chosen to illustrate my earlier points, but the stage _IS_
operated Class A with the plate current between cutoff and saturation.

Since the "rec"groups are not supposed to have binaries in them, I placed
the graphics as PDF attachments to a post entitled "Harmonics generated by
a Class A stage" in the "alt.binaries.ham-radio" newsgroup. If anyone
wishes to see these curves and their newsgroup provider does not provide
this group, I apologize. I believe Google Groups may not provide binaries,
so I suggest getting a real newsreader and a good newsfeed.

The first graph is entitled "Transconductance.pdf" and it shows the plate
current as a function of the grid voltage. This data was obtained directly
from the General Electric datasheet, ET-T1604 dated March, 1960. Since
Excel stinks when plotting and doing calculations with data that is not
best expressed in a bar chart, I used an evaluation copy of PSIPlot from
Poly Software International (http://www.polysoftware,com) to generate the
plots. {Real scientists and engineers never use a bar chart except when
making presentations to brain challenged management!} :-)

The driving waveform and the resultant plate current waveform are shown in
the graph entitled "Waveforms.pdf". The obvious flattening is due to
cutoff being approached at the crest of the driving waveform. After all,
the transconductance curve is not perfectly a straight line.

Finally, the spectrum of current waveform is plotted in the graph called
"Spectrum.pdf". The spectrum has been normalized with respect to the DC
output. The scale of the X-axis is slightly off but it was not worth my
time correcting it. The fundamental is about 60 to 70 percent of the DC
output, and the second harmonic is about 40 percent of the DC output. All
higher harmonic are less than one percent of the DC output except the
fifth. Higher harmonics are still greater than one tenth of a percent of
the DC up to the _13th_ harmonic. Harmonics beyond the 14th are still
readily measured.

In conclusion, even single ended Class A amplifiers generate harmonics.
If a lower driving voltage were used, the amplitudes of the harmonics would
be reduced, but the fundamental would also be reduced. Please follow-up to
the "rec.radio.amateur.homebrew" newsgroup. Golden-eared audiophools will
be ignored.

73, Dr. Barry L. Ornitz WA4VZQ

On Mon, 15 Dec 2008 23:29:35 -0500, "NoSPAM"
wrote:

"Telstar Electronics" wrote in message
...

You mean to tell me that you take a clean sine wave... pass it
through... say a single-ended class A amp... and you can put a tank on
the output of that amplifier... and tune for a harmonic? You will get
nothing.

Of course you will. No active device is perfect.

I decided to illustrate the fact that a single ended triode operated in
Class A can produce harmonics. For a tube, I used a 6C4 (1/2 of a 12AU7)
operated with 300 volts on the plate, a grid bias voltage of -7 volts,
driven with a pure sine wave of 14 volts peak-to-peak. The high driving
voltage was chosen to illustrate my earlier points, but the stage _IS_
operated Class A with the plate current between cutoff and saturation.

Did you bypass the cathode resistor or not ?

All active elements are more or less nonlinear, so if you need more or
less linear amplification, you need to use feedback/feedforward.

A non-bypassed cathode/emitter resistor will greatly improve the
linearity of a single stage.

Paul OH3LWR

On Tue, 16 Dec 2008, Paul Keinanen wrote:

Date: Tue, 16 Dec 2008 09:47:22 +0200
From: Paul Keinanen
Newsgroups: rec.radio.amateur.homebrew
Subject: Doubling

On Mon, 15 Dec 2008 23:29:35 -0500, "NoSPAM"
wrote:

"Telstar Electronics" wrote in message
...

You mean to tell me that you take a clean sine wave... pass it
through... say a single-ended class A amp... and you can put a tank on
the output of that amplifier... and tune for a harmonic? You will get
nothing.

Of course you will. No active device is perfect.

I decided to illustrate the fact that a single ended triode operated in
Class A can produce harmonics. For a tube, I used a 6C4 (1/2 of a 12AU7)
operated with 300 volts on the plate, a grid bias voltage of -7 volts,
driven with a pure sine wave of 14 volts peak-to-peak. The high driving
voltage was chosen to illustrate my earlier points, but the stage _IS_
operated Class A with the plate current between cutoff and saturation.

Did you bypass the cathode resistor or not ?

I did the same experiment that he did (6C4) only ran the cathod at
chassis, and grid through an RF choke, and 100 vDC on plate, and drove at
about 1/2-1 volt and that is zero bias, no need for cathode cap bypass, and
I got gain and second harmonic.

All active elements are more or less nonlinear, so if you need more or
less linear amplification, you need to use feedback/feedforward.

A non-bypassed cathode/emitter resistor will greatly improve the
linearity of a single stage.

I'm still waiting for any "expert" comments from anyone who would care to
speculate on the contributions, from oscillator harmonic content vs
contribution from harmonic distortion in the amplifier.

Paul OH3LWR

On Dec 15, 11:29*pm, "NoSPAM" wrote:
"Telstar Electronics" wrote in message

...

You mean to tell me that you take a clean sine wave... pass it
through... say a single-ended class A amp... and you can put a tank on
the output of that amplifier... and tune for a harmonic? You will get
nothing.

Of course you will. *No active device is perfect.

Hey OM
The nature of the beast is:
single ended amps produce rich even harmonics
Push Pull amps produce rich odd harmonics

so you can gits odd harmonics from single ended but they are poor like
me.

73 OM
n8zu