"Bill Janssen" wrote in message
...
NoSPAM wrote:
"Telstar Electronics"
wrote in message
...
On Nov 22, 8:43 pm, Stray Dog
wrote:
? Despite what at least one other person responding to this said, I can
rest
assure you that if you run a doubler/multiplier stage even in a
linear
mode, AND if you tune the output of that stage to the multiple
harmonic,
you will definitely get output at that harmonic frequency which is
stronger than the input drive voltage.

Huh? No way... you MUST have non-linearities to make a doubler.
Actually you do not need any nonlinearity to make a doubler
(quadrupler, etc.).
Assume you have two Class B (or AB) stages that are driven in
push-pull. The outputs are connected in parallel. And to make things
even more linear, let each stage have a resistive load. Each stage will
produce a linearly amplified (but inverted) version of the input signal
FOR THE POSITIVE HALF of the driving waveform only. Being driven 180
degrees out of phase with the input signal, the second stage will
produce a linearly amplified but (again inverted) version of the input
signal FOR THE NEGATIVE HALF of the driving waveform. Both outputs will
have a DC offset of the plate (collector, drain) voltage.
Class B or even Class AB in the circuit you described are non-linear. Try
that circuit
with Class A biasing.

Bill K7NOM


All that is really required is that the active devices have a different
gain with positive input signals than with negative input signals. This is
easily achieved with Class B and Class AB stages. As long as both stages
are identical the fundamental and odd order harmonics will cancel. You are
correct that with two Class A stages where the gain is identical for either
polarity of input, the output signal will perfectly cancel. To make the
method work here, you could synchronously switch the input signal between
two perfectly linear stages. My point was that a full-wave rectified
signal contains only even order harmonics.

In the real world, as Stray Dog pointed out, ALL amplifier stages are
nonlinear to some degree. The reason that Class AB and B amplifiers are
considered linear RF amplifiers is that the tuned circuit on the output
supplies supplies the "missing half" of the waveform. Without the tuned
circuit, harmonics of the 2nd, 4th, 6th, etc. order as well as the
fundamental are present. Odd order harmonics are only found if the gain is
nonlinear for positive input signals. The tuned output stage passes the
fundamental and suppresses the harmonics.

Thanks for pointing this out, Bill.

73, Barry WA4VZQ

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

On Sun, 14 Dec 2008, NoSPAM wrote:

Date: Sun, 14 Dec 2008 23:27:11 -0500
From: NoSPAM
Newsgroups: rec.radio.amateur.homebrew
Followup-To: rec.radio.amateur.homebrew
Subject: Doubling

"Bill Janssen" wrote in message
...
NoSPAM wrote:
"Telstar Electronics"
wrote in message
...
On Nov 22, 8:43 pm, Stray Dog
wrote:
? Despite what at least one other person responding to this said, I can
rest
assure you that if you run a doubler/multiplier stage even in a
linear
mode, AND if you tune the output of that stage to the multiple
harmonic,
you will definitely get output at that harmonic frequency which is
stronger than the input drive voltage.

Huh? No way... you MUST have non-linearities to make a doubler.
Actually you do not need any nonlinearity to make a doubler (quadrupler,
etc.).
Assume you have two Class B (or AB) stages that are driven in push-pull.
The outputs are connected in parallel. And to make things even more
linear, let each stage have a resistive load. Each stage will produce a
linearly amplified (but inverted) version of the input signal FOR THE
POSITIVE HALF of the driving waveform only. Being driven 180 degrees out
of phase with the input signal, the second stage will produce a linearly
amplified but (again inverted) version of the input signal FOR THE
NEGATIVE HALF of the driving waveform. Both outputs will have a DC offset
of the plate (collector, drain) voltage.
Class B or even Class AB in the circuit you described are non-linear. Try
that circuit
with Class A biasing.

Bill K7NOM


All that is really required is that the active devices have a different gain
with positive input signals than with negative input signals. This is easily
achieved with Class B and Class AB stages. As long as both stages are
identical the fundamental and odd order harmonics will cancel. You are
correct that with two Class A stages where the gain is identical for either
polarity of input, the output signal will perfectly cancel. To make the
method work here, you could synchronously switch the input signal between two
perfectly linear stages. My point was that a full-wave rectified signal
contains only even order harmonics.

In the real world, as Stray Dog pointed out, ALL amplifier stages are
nonlinear to some degree. The reason that Class AB and B amplifiers are
considered linear RF amplifiers is that the tuned circuit on the output
supplies supplies the "missing half" of the waveform. Without the tuned
circuit, harmonics of the 2nd, 4th, 6th, etc. order as well as the
fundamental are present. Odd order harmonics are only found if the gain is
nonlinear for positive input signals. The tuned output stage passes the
fundamental and suppresses the harmonics.

Thanks for pointing this out, Bill.

73, Barry WA4VZQ


I'll just add a footnote. When I actually built a few "buffer" amplifiers
(tube jobs, 12BY7s, 6AG7s, etc), and for the hell of it, hooked up my
scope (an old Tektronix solid state scope with one microsecond/div
timebase, max) and actually looked at the sine wave (it looked 'nice' by
the way) and then tuned the air variable through both the fundamental or
the second harmonic (and I'm talking about 2-3 mHz signal source), I was
amazed to be able to easily see the extra "peaks" come out of the
"valleys" of the fundamental and I'm running these tubes at zero bias, low
plate voltage, too. Look in the tube manuals for any class C tube and they
talk about -50 to -70 v, grid negative wrt cathode. Class B and below talk
about negative bias much lower but still pretty negative.

Like I said, I was surprised. This _should_ be discussed in the ARRL
handbooks (maybe it is, but I couldn't find it [maybe I didn't look hard
enough?]) and it would be worth 1-2 pages to show everyone what these
signals have in them.

Here is another goodie (true story). R-390 local oscillator (runs 2.4 to
3.4 mHz, single 6BA6 tube). Had it set to about 3 mHz and looking at that
"nice" (I have no harmonic meter to measure distortion) sine wave on the
scope, and I "loaded down" the oscillator output lead with a tuned circuit
and tuned that circuit to about 6 mHz. Guess what? Got double the number
of peaks on the scope, just as with the linear amplifier. All calculate
out on peaks vs time base divisions. So? Does anyone want to suggest that
having the output LC circuit of an LC free-running oscillator tuned to
double the frequency of the LC circuit is making it "oscillate" on its
second overtone? ;-)

Yeah, I checked resonant frequencies with a GDO on all this stuff, too.
I'm not making any of this up.

For the record, I also have an old Knight Kit RF oscillator (100Kc to 400
mHz on 3rd harmonic) and put that into my scope and the waveform looks
like crap (but you can pick up the signal on a SW receiver set to where
the scale matches the frequency of the oscillator). And, the
shape of the crap changes from one end of the band to
the other. Also have an old HP audio oscillator (high quality stuff) and
it puts out a _very_ 'nice' sine wave no matter where in the range you set
the dial (one Hz to 200 kHz).

73 all,