Discussion:
Suppressor-grid modulation
(too old to reply)
Antonio Vernucci
2011-01-16 18:19:33 UTC
Permalink
I am planning to build a suppressor-grid modulated AM transmitter.

In all the diagrams I have seen they use proper pentodes, i.e. tubes that have a
real suppressor grid (e.g. 803).

I have seen no diagram using beam power tubes (e.g. 813 or 814) which have beam
forming plates instead of the suppressor grid .

Before purchasing 803 tubes, I would like to be sure that 813s or 814s are
really unsuitable for suppressor-grid modulation.

My question is whether, with 813s or 814s, the plate current can be actually
controlled by varying the beam forming plates voltage.

Does anyone have experience on that issue?

73

Tony I0JX

Rome, Italy
Piero Soldi
2011-01-16 21:05:19 UTC
Permalink
Post by Antonio Vernucci
I am planning to build a suppressor-grid modulated AM transmitter.
In all the diagrams I have seen they use proper pentodes, i.e. tubes
that have a real suppressor grid (e.g. 803).
I have seen no diagram using beam power tubes (e.g. 813 or 814) which
have beam forming plates instead of the suppressor grid .
Before purchasing 803 tubes, I would like to be sure that 813s or 814s
are really unsuitable for suppressor-grid modulation.
My question is whether, with 813s or 814s, the plate current can be
actually controlled by varying the beam forming plates voltage.
Does anyone have experience on that issue?
73
Tony I0JX
Rome, Italy
Hello Tony, de Piero I5SPO.

Quite a ( very ) long time ago, i've done an A.M. TX with a
Geloso VFO and a class C RL12P35 Wehrmacht pentode, whose
characteristics are similar to 1625 ( a.k.a. 807 with
12.6 v filament ), using a carbon mike and a step-up
audio transformer.

I believe that, using beam tetrodes, there's no way... :-(

I know also 813 and 814 ( have 2 pcs ) and these, like 807,
are useful for controlled carrier A.M. by modulating screen grid.

Do not know 803, but if i remember well, are low power tubes.

Used with suppressor modulation, their output will be one fourth
of CW rated output, and efficiency is consequently low... :-(

HTH,

73, Piero.
Antonio Vernucci
2011-01-16 22:04:36 UTC
Permalink
Post by Piero Soldi
Hello Tony, de Piero I5SPO.
Quite a ( very ) long time ago, i've done an A.M. TX with a
Geloso VFO and a class C RL12P35 Wehrmacht pentode, whose
characteristics are similar to 1625 ( a.k.a. 807 with
12.6 v filament ), using a carbon mike and a step-up
audio transformer.
I believe that, using beam tetrodes, there's no way... :-(
I know also 813 and 814 ( have 2 pcs ) and these, like 807,
are useful for controlled carrier A.M. by modulating screen grid.
Do not know 803, but if i remember well, are low power tubes.
Used with suppressor modulation, their output will be one fourth
of CW rated output, and efficiency is consequently low... :-(
HTH,
73, Piero.
Hi Piero,

the 803 is about the same as the 813, though it has a proper suppressor screen.
Other differences are socket (5 pin vs. 7 pin) and maximum frequency (20 MHz
against 30 MHz).

What I need to know is if any one has ever tried to vary the 813 beam forming
plate voltage, so as to verify whether the plate current can so be controlled.
If so, I could avoid to purchase the 803s and use the 813s I already have.

I know that with suppressor screen modulation output power is about one fourth,
but efficiency will not be so low because, in absence of modulation, also the
input power decreases (by somewhat less than one fourth). With a pair of 803s
(or 813s I hope!) I should obtain about 200W of unmodulated carrier power,
peaking at 800W under 100% modulation.

I used to have a few RL12P35s, though I never actually used them. A Radio
Rivista article by Dante I1DC describes a transmitter using the RL12P50 (a
bigger brother of the RL12P35). But all those tubes are too small for well
exploiting the potential advantages of suppressor screen modulation. As a matter
of fact the advantage of not having to build a powerful modulator becomes more
evident when the needed modulator would be real big!

73

Tony I0JX
Barry
2011-01-16 23:51:51 UTC
Permalink
Post by Antonio Vernucci
Post by Piero Soldi
Hello Tony, de Piero I5SPO.
Quite a ( very ) long time ago, i've done an A.M. TX with a
Geloso VFO and a class C RL12P35 Wehrmacht pentode, whose
characteristics are similar to 1625 ( a.k.a. 807 with
12.6 v filament ), using a carbon mike and a step-up
audio transformer.
I believe that, using beam tetrodes, there's no way... :-(
I know also 813 and 814 ( have 2 pcs ) and these, like 807,
are useful for controlled carrier A.M. by modulating screen grid.
Do not know 803, but if i remember well, are low power tubes.
Used with suppressor modulation, their output will be one fourth
of CW rated output, and efficiency is consequently low... :-(
HTH,
73, Piero.
Hi Piero,
the 803 is about the same as the 813, though it has a proper suppressor
screen. Other differences are socket (5 pin vs. 7 pin) and maximum
frequency (20 MHz against 30 MHz).
What I need to know is if any one has ever tried to vary the 813 beam
forming plate voltage, so as to verify whether the plate current can so
be controlled. If so, I could avoid to purchase the 803s and use the
813s I already have.
I know that with suppressor screen modulation output power is about one
fourth, but efficiency will not be so low because, in absence of
modulation, also the input power decreases (by somewhat less than one
fourth). With a pair of 803s (or 813s I hope!) I should obtain about
200W of unmodulated carrier power, peaking at 800W under 100%
modulation.
I used to have a few RL12P35s, though I never actually used them. A
Radio Rivista article by Dante I1DC describes a transmitter using the
RL12P50 (a bigger brother of the RL12P35). But all those tubes are too
small for well exploiting the potential advantages of suppressor screen
modulation. As a matter of fact the advantage of not having to build a
powerful modulator becomes more evident when the needed modulator would
be real big!
73
Tony I0JX
True pentodes are needed for suppressor grid modulation. The beam
forming plates have much less of an effect on plate current and trying to
use them for modulation will result in a highly nonlinear modulation
waveform. Remember that emission current not going to the plate will
instead go to the screen grid. The power dissipation of the screen grid
is what seriously limits the use of suppressor modulation.

If you already have the sockets for the 813, I would suggest the use of
4E27A/5-125B tubes. The 4E27/Heintz & Kaufman 257B has less plate
dissipation, but it too might be suitable.

Please let me know if you need datasheets for either of these tubes and
for the 803.

73, Barry WA4VZQ wa4vzq(-at-)live(-dot-)com
Antonio Vernucci
2011-01-17 20:39:47 UTC
Permalink
True pentodes are needed for suppressor grid modulation. The beam forming
plates have much less of an effect on plate current and trying to use them for
modulation will result in a highly nonlinear modulation waveform. Remember
that emission current not going to the plate will instead go to the screen
grid. The power dissipation of the screen grid is what seriously limits the
use of suppressor modulation.
If you already have the sockets for the 813, I would suggest the use of
4E27A/5-125B tubes. The 4E27/Heintz & Kaufman 257B has less plate
dissipation, but it too might be suitable.
Please let me know if you need datasheets for either of these tubes and for
the 803.
73, Barry WA4VZQ wa4vzq(-at-)live(-dot-)com
Hi Barry,

thanks for the tips. However, looking at the tubes characteristics, the main
advantage of the 4E27 w.r.t. the 803 is the possibility to work at much higher
frequencies (apart form the socket, which can however be simply changed with no
need to make extra holes on the chassis). For the rest, it has a lower plate
dissipation (65W against 125W), different filament voltage and it costs more
(38$ against 25$).

I appreciate the screen grid dissipation problem but it is not clear to me why
your statement "that emission current not going to the plate will instead go to
the screen grid" would not equally apply if the tube has a proper suppressor
grid instead of bram forming plates. Could you please clarify?

73

Tony I0JX
Nordic Breeds WA4VZQ
2011-01-18 04:45:21 UTC
Permalink
Post by Antonio Vernucci
Post by Barry
True pentodes are needed for suppressor grid modulation. The beam
forming plates have much less of an effect on plate current and trying
to use them for modulation will result in a highly nonlinear
modulation waveform. Remember that emission current not going to the
plate will instead go to the screen grid. The power dissipation of
the screen grid is what seriously limits the use of suppressor
modulation.
If you already have the sockets for the 813, I would suggest the use
of 4E27A/5-125B tubes. The 4E27/Heintz & Kaufman 257B has less plate
dissipation, but it too might be suitable.
Please let me know if you need datasheets for either of these tubes
and for the 803.
73, Barry WA4VZQ wa4vzq(-at-)live(-dot-)com
Hi Barry,
thanks for the tips. However, looking at the tubes characteristics, the
main advantage of the 4E27 w.r.t. the 803 is the possibility to work at
much higher frequencies (apart form the socket, which can however be
simply changed with no need to make extra holes on the chassis). For
the rest, it has a lower plate dissipation (65W against 125W),
different filament voltage and it costs more (38$ against 25$).
I appreciate the screen grid dissipation problem but it is not clear
to me why your statement "that emission current not going to the plate
will instead go to the screen grid" would not equally apply if the tube
has a proper suppressor grid instead of bram forming plates. Could you
please clarify?
73
Tony I0JX
Actually I did _not_ do a good job of explaining this. In a pentode, the
suppressor grid controls the ratio of the emission current going to the
screen to that going to the plate. It also eliminates the problem of
secondary emission. Beam forming plates are specifically designed to
control secondary emission, but they have much less of an effect of
controlling plate current. Rather than going into detail here, allow me
to refer you to Karl Spangenberg's book, "Vacuum Tubes." This book is
now available on several websites. Chapter 11 goes into great detail on
how both pentodes and beam power tubes work and how they differ. I would
also refer you to O. H Schade's classic paper, "Beam Power Tubes," which
is also available on many of the same websites. Pete Millet's site is my
favorite with many excellent technical books. http://www.pmillett.com
One trick to reduce screen grid dissipation in suppressor modulated
pentodes is to power the screen grid with a voltage dropping resistor
from the plate supply rather than use an independent supply.

While not available in power tubes, many receiving pentodes are designed
such that the suppressor grid acts much like the grid in terms of its
transconductance. The 6AS6 is probably the earliest example of such
tubes. They make good mixers.

73, Barry WA4VZQ
Antonio Vernucci
2011-01-18 20:34:16 UTC
Permalink
Post by Nordic Breeds WA4VZQ
Actually I did _not_ do a good job of explaining this. In a pentode, the
suppressor grid controls the ratio of the emission current going to the screen
to that going to the plate. It also eliminates the problem of secondary
emission. Beam forming plates are specifically designed to control secondary
emission, but they have much less of an effect of controlling plate current.
Rather than going into detail here, allow me to refer you to Karl
Spangenberg's book, "Vacuum Tubes." This book is now available on several
websites. Chapter 11 goes into great detail on how both pentodes and beam
power tubes work and how they differ. I would also refer you to O. H Schade's
classic paper, "Beam Power Tubes," which is also available on many of the same
websites. Pete Millet's site is my favorite with many excellent technical
books. http://www.pmillett.com
One trick to reduce screen grid dissipation in suppressor modulated pentodes
is to power the screen grid with a voltage dropping resistor from the plate
supply rather than use an independent supply.
While not available in power tubes, many receiving pentodes are designed such
that the suppressor grid acts much like the grid in terms of its
transconductance. The 6AS6 is probably the earliest example of such tubes.
They make good mixers.
73, Barry WA4VZQ
Thanks for your answer.

A negative suppressor grid then tends to "isolate" the plate from the rest of
the tube.

So, the effect is similar to when, if the plate voltage of a power audio
amplifier stage is removed by accident, the screen gets quickly destroyed due to
excessive power dissipation.

I shall then carefully check the screen dissipation in the suppressor-modulated
transmitter I am planning to buld.

Thanks and 73

Tony I0JX
coffelt2
2011-01-18 02:44:19 UTC
Permalink
Post by Antonio Vernucci
I am planning to build a suppressor-grid modulated AM transmitter.
In all the diagrams I have seen they use proper pentodes, i.e. tubes that
have a real suppressor grid (e.g. 803).
I have seen no diagram using beam power tubes (e.g. 813 or 814) which have
beam forming plates instead of the suppressor grid .
Before purchasing 803 tubes, I would like to be sure that 813s or 814s are
really unsuitable for suppressor-grid modulation.
My question is whether, with 813s or 814s, the plate current can be
actually controlled by varying the beam forming plates voltage.
Does anyone have experience on that issue?
This does not answer the question, but is offered as a bit of homebrew
lore.
After WWII, the 1625's were plentiful and cheap. Some Ham found that with
certain brands of 1625's, the suppressor grid was not tied to the cathode
inside the glass envelope. The two were tied together inside the tube base.
So, after removing the base, the two elements could be separated from each
other.
The aim was, guess what? Suppressor-grid modulation! I can remember
hearing some of these rigs on the air. I don't know just what percentage of
modulation was possible, but I remember it being pretty weak. Good strong
signal with very low modulation level.
The aim had been to use what parts one had, and it surely was an
inexpensive
way to join the AM crowd!

Old Chief Lynn, W7LTQ
Nordic Breeds WA4VZQ
2011-01-18 04:50:58 UTC
Permalink
Post by coffelt2
This does not answer the question, but is offered as a bit of
homebrew lore.
After WWII, the 1625's were plentiful and cheap. Some Ham found that with
certain brands of 1625's, the suppressor grid was not tied to the cathode
inside the glass envelope. The two were tied together inside the tube base.
So, after removing the base, the two elements could be separated from each
other.
The aim was, guess what? Suppressor-grid modulation! I can remember
hearing some of these rigs on the air. I don't know just what
percentage of
modulation was possible, but I remember it being pretty weak. Good strong
signal with very low modulation level.
The aim had been to use what parts one had, and it surely was an
inexpensive
way to join the AM crowd!
Old Chief Lynn, W7LTQ
In the 1957 ARRL Handbook, these particular tubes were also used in a
cathode driven (grounded grid) amplifier.

73, Barry WA4VZQ
Antonio Vernucci
2011-01-18 20:39:20 UTC
Permalink
Post by coffelt2
The aim was, guess what? Suppressor-grid modulation! I can remember
hearing some of these rigs on the air. I don't know just what percentage of
modulation was possible, but I remember it being pretty weak. Good strong
signal with very low modulation level.
The aim had been to use what parts one had, and it surely was an
inexpensive
way to join the AM crowd!
Old Chief Lynn, W7LTQ
In the 1957 ARRL Handbook, these particular tubes were also used in a cathode
driven (grounded grid) amplifier.
73, Barry WA4VZQ
Yes, I was aware of the "modified 1625" but for linear amplifier usage. Now I
know that they were also used for suppressor-grid modulated stages.

But now a doubt come to my mind: the 1625 is a beam-power tube, not a pentode
(actually it is an 807 with 12.6V filament). So, how could it work in
suppressor-grid modulated stages?

73

Tony I0JX
Nordic Breeds WA4VZQ
2011-01-19 00:01:25 UTC
Permalink
Post by Antonio Vernucci
Post by Nordic Breeds WA4VZQ
Post by coffelt2
The aim was, guess what? Suppressor-grid modulation! I can remember
hearing some of these rigs on the air. I don't know just what percentage of
modulation was possible, but I remember it being pretty weak. Good strong
signal with very low modulation level.
The aim had been to use what parts one had, and it surely was an
inexpensive
way to join the AM crowd!
Old Chief Lynn, W7LTQ
In the 1957 ARRL Handbook, these particular tubes were also used in a
cathode driven (grounded grid) amplifier.
73, Barry WA4VZQ
Yes, I was aware of the "modified 1625" but for linear amplifier usage.
Now I know that they were also used for suppressor-grid modulated
stages.
But now a doubt come to my mind: the 1625 is a beam-power tube, not a
pentode (actually it is an 807 with 12.6V filament). So, how could it
work in suppressor-grid modulated stages?
73
Tony I0JX
Read Lynn's post again. He said the carrier was strong but the audio was
quite weak. It is quite difficult to get over 95% modulation with a
suppressor modulator. With beam power tubes, you get far less than this.
Also you get lots of distortion because the beam forming plates do not
linearly control plate current, so you have to lower the modulation level
even further to make the audio readable by listeners. Hence the "strong
signal with very low modulation level" makes sense. Fortunately with
pentodes, it is easy to drive the output to zero (negative modulation).
The real problem occurs when the suppressor is driven very far into the
positive voltage region and it starts drawing current. Typically the
suppressor grid can only dissipate a few watts. Since current is drawn
during the positive peaks, an audio driver must present a low impedance.

73, Barry WA4VZQ
Scott Dorsey
2011-01-19 01:08:45 UTC
Permalink
Post by Nordic Breeds WA4VZQ
Read Lynn's post again. He said the carrier was strong but the audio was
quite weak. It is quite difficult to get over 95% modulation with a
suppressor modulator. With beam power tubes, you get far less than this.
Also you get lots of distortion because the beam forming plates do not
linearly control plate current, so you have to lower the modulation level
even further to make the audio readable by listeners. Hence the "strong
signal with very low modulation level" makes sense.
My experience was about 25% modulation, and that was with distortion that
was... well... kind of bad.

I would characterize this as pretty much the worst quality AM ever, worse
than screen grid modulation by a long shot.
Post by Nordic Breeds WA4VZQ
Fortunately with
pentodes, it is easy to drive the output to zero (negative modulation).
The real problem occurs when the suppressor is driven very far into the
positive voltage region and it starts drawing current. Typically the
suppressor grid can only dissipate a few watts. Since current is drawn
during the positive peaks, an audio driver must present a low impedance.
And this also quickly becomes a distortion source unless the audio driver
stage is pretty hefty.

Just say no.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
coffelt2
2011-01-19 03:09:17 UTC
Permalink
Fortunately with
Post by Nordic Breeds WA4VZQ
pentodes, it is easy to drive the output to zero (negative modulation).
The real problem occurs when the suppressor is driven very far into the
positive voltage region and it starts drawing current. Typically the
suppressor grid can only dissipate a few watts. Since current is drawn
during the positive peaks, an audio driver must present a low impedance.
73, Barry WA4VZQ
Ah, yes, "(negative modulation)"!

You seem to be "hep" on old stuff, do you remember "negative peak
clipping"?
I thought I was in Heaven in about 1958 with a single 2E26 final on 15
Meters.
In class C, with a pair of 6L6 modulators, push-pull, class AB1, and used a
VR
tube across the modulation transformer secondary clipping the negative
peaks, while
allowing the positive peaks to go "over" 100%.

Technical gurus of the day poo-poo'd the scheme. It looked a little
rough on the
scope, but unsolicited signal reports said it "packed a lot of modulation".
I am thinking it must have been a little like more modern amateur
"speech
processing"

I also seem to remember those modified 1646's getting almost 20%
suppressor
grid modulation after tinkering around with power supply voltages.

Old Chief Lynn, W7LTQ
Edmund H. Ramm
2011-01-19 22:28:09 UTC
Permalink
[...]
used a VR tube across the modulation transformer secondary clipping
the negative peaks, while allowing the positive peaks to go "over" 100%.
[...]
It's still being done today, albeit using silicon diodes and
resistors. Just look up the articles on "Negative Cycle Loading"
in Electric Radio magazine.

73, Eddi ._._.
--
e-mail: dk3uz AT arrl DOT net | AMPRNET: ***@db0hht.ampr.org
If replying to a Usenet article, please use above e-mail address.
Linux/m68k, the best U**x ever to hit an Atari!
Nordic Breeds WA4VZQ
2011-01-19 23:41:54 UTC
Permalink
Post by coffelt2
Ah, yes, "(negative modulation)"!
You seem to be "hep" on old stuff, do you remember "negative peak
clipping"?
I thought I was in Heaven in about 1958 with a single 2E26 final on 15
Meters.
In class C, with a pair of 6L6 modulators, push-pull, class AB1, and
used a VR
tube across the modulation transformer secondary clipping the negative
peaks, while
allowing the positive peaks to go "over" 100%.
Technical gurus of the day poo-poo'd the scheme. It looked a little
rough on the
scope, but unsolicited signal reports said it "packed a lot of
modulation".
I am thinking it must have been a little like more modern amateur
"speech
processing"
I also seem to remember those modified 1646's getting almost 20%
suppressor
grid modulation after tinkering around with power supply voltages.
Old Chief Lynn, W7LTQ
Hi Lynn,

A pair of 6L6's to modulate a 2E26... there was enough audio to drive a
6146 with a some to spare and enough to really overmodulate a 2E26! :-)

Negative peak clipping was based on a diode with its anode connected to
B+ and its cathode connected to the output side of the modulation
transformer. This would allow the final's voltage to drop to only a few
volts during negative modulation peaks. Later refinement was to add a
gaseous voltage regulator tube between the diode's cathode and the output
side of the transformer. In this case, the final's voltage would only
drop to a voltage determined by the regulator tube. Today a silicon
diode might be used, and zeners would replace the VR tube. The result of
this circuit was that the RF would never be completely cut off during
negative modulation peaks. Positive modulation peaks would be passed
allowing higher positive modulation. This is what gave the higher "talk
power." It still caused distortion, but much less than that if the
negative peaks were not clipped.

Everyone's voice is asymmetric. If you look at the voice waveform with
an oscilloscope, you will see that peaks on one side of zero are often
considerably higher that the opposite polarity. The average is still
zero, however. The peak is caused by harmonics in the voice being in
phase with each other. This property can be used to advantage in
amplitude modulation by having the peaks occur on the positive
modulation. Usually all that was needed to put the peak on the right
side was to reverse the connections to the modulation transformer or to
reverse the connections to the microphone.

I am sure Scott Dorsey knows more about this than I do, but CBS produced
two devices called the Audimax and Volumax that shifted the phase of the
audio as a function of frequency. Another term for these devices is
phase rotator. Kahn Communications also was in the market with its
SymmetraPeak. To the ear, the sound was unchanged, but to the
transmitter, the peaks became symmetrical. There is an excellent
discussion of these devices on James Tonne's (W4ENE) website
http://www.tonnesoftware.com/appnotes/allpass/allpass.html and on Gary
Blau's (W3AM) website http://www.w3am.com/8poleapf.html. {A biased
opinion here — Jim's site contains some _excellent_ free software.}

As to being "hep" on old technology, I appreciate the compliment. As an
undergraduate, my university taught tubes and transistors. By the time I
got to graduate school, tubes were no longer taught. By the time I got
out of graduate school, integrated circuits were the "in thing" and
microprocessors had just begun. I do have a good collection of older
engineering books, however. I am constantly amazed by the technology of
the late 1920's and the 1930's. And it was all designed without the
benefit of computers! While I haven't used it in years, I still have my
K&E metal log-log-decitrig slide rule, and the bamboo rule I used while
in high school.

73, Barry WA4VZQ
Scott Dorsey
2011-01-21 14:43:35 UTC
Permalink
Post by Nordic Breeds WA4VZQ
I am sure Scott Dorsey knows more about this than I do, but CBS produced
two devices called the Audimax and Volumax that shifted the phase of the
audio as a function of frequency. Another term for these devices is
phase rotator. Kahn Communications also was in the market with its
SymmetraPeak. To the ear, the sound was unchanged, but to the
transmitter, the peaks became symmetrical. There is an excellent
discussion of these devices on James Tonne's (W4ENE) website
http://www.tonnesoftware.com/appnotes/allpass/allpass.html and on Gary
Blau's (W3AM) website http://www.w3am.com/8poleapf.html. {A biased
opinion here — Jim's site contains some _excellent_ free software.}
The original Audimax/Volumax combination had no phase rotator. I worked
at an AM station that used them, and the chief engineer had installed a
phase reverse switch on the announcer mike and auditioned each announcer
to tell them which position to use. (Apparently they had used figure-8
mikes a year or so before I got there, and the announcers just used the
front of back of the mikes).

A lot of stations using the Audimax/Volumax would also have a phase
rotator in the chain, though. CRL made a popular one, and so did Garron.
Some folks made some boards tht dropped inside the Volumax for it too,
but I never used any of those. I went to the Optimod as soon as I could,
and it has a great phase rotator.

The phase rotator is a hell of a great gadget, it gives you a lot of loudness
without any perceived distortion. Mind you, for communications applications
it's no more effective just than aggressive clipping, but there are folks
who don't want aggressive clipping.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
Nordic Breeds WA4VZQ
2011-01-21 18:42:47 UTC
Permalink
Post by Scott Dorsey
The original Audimax/Volumax combination had no phase rotator. I worked
at an AM station that used them, and the chief engineer had installed a
phase reverse switch on the announcer mike and auditioned each
announcer
to tell them which position to use. (Apparently they had used figure-8
mikes a year or so before I got there, and the announcers just used the
front or back of the mikes).
A lot of stations using the Audimax/Volumax would also have a phase
rotator in the chain, though. CRL made a popular one, and so did Garron.
Some folks made some boards that dropped inside the Volumax for it too,
but I never used any of those. I went to the Optimod as soon as I could,
and it has a great phase rotator.
The phase rotator is a hell of a great gadget, it gives you a lot of loudness
without any perceived distortion. Mind you, for communications applications
it's no more effective just than aggressive clipping, but there are folks
who don't want aggressive clipping.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
Thanks for the corrections, Scott.

Aggressive clipping creates a ton of distortion unless the voice signal
is split into several bands, each processed and filtered, and then
combined. The phase rotator theoretically produces no amplitude
distortion, and due to the way the human ear works, the shifting of the
phases is not heard. I read once that the cochlea and its nerves
perform physiologically something akin to a mathematician performing a
Fourier analysis. I find it amazing that we process sound, for the most
part, on the amplitude versus frequency information, and ignore the phase
versus frequency information.

With modern operational amplifiers, it is fairly simple to produce a good
phase rotator using cascaded all-pass networks. I would hate to have to
manufacture the original SymmetraPeak with its inductor-capacitor network
lattices.

Well, we are pretty far from the original subject, but I have enjoyed the
discussion. However I do have a Boatanchor question.

I remember seeing ads in QST in the 1960's for a device I think was
called "Echoplex." It was supposedly used on commercial and military
voice communications circuits. I never heard one of these in use by a
ham, probably because their cost could buy several Collins S-Line
stations. Doing a Google search brings up lots of echo-effects
processors for guitars and such, but I found nothing for communication
usage. Do any readers here remember the device and its manufacturer and
how it worked?

73, Barry WA4VZQ
Scott Dorsey
2011-01-21 20:09:46 UTC
Permalink
Post by Nordic Breeds WA4VZQ
Aggressive clipping creates a ton of distortion unless the voice signal
is split into several bands, each processed and filtered, and then
combined. The phase rotator theoretically produces no amplitude
distortion, and due to the way the human ear works, the shifting of the
phases is not heard.
Right. I think for communications use, though, the ton of distortion can
actually help intelligibility of consonants under bad conditions. Certainly
it gives you a distinctive sound in a pileup.
Post by Nordic Breeds WA4VZQ
I remember seeing ads in QST in the 1960's for a device I think was
called "Echoplex." It was supposedly used on commercial and military
voice communications circuits. I never heard one of these in use by a
ham, probably because their cost could buy several Collins S-Line
stations. Doing a Google search brings up lots of echo-effects
processors for guitars and such, but I found nothing for communication
usage. Do any readers here remember the device and its manufacturer and
how it worked?
I have only heard of the echo-effect box. "Everything I use must have
X in it, like sex and echoplex" says Lee Scratch Perry.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
Gaius
2011-01-22 14:14:41 UTC
Permalink
Post by Nordic Breeds WA4VZQ
I remember seeing ads in QST in the 1960's for a device I think was
called "Echoplex." It was supposedly used on commercial and military
voice communications circuits. I never heard one of these in use by a
ham, probably because their cost could buy several Collins S-Line
stations. Doing a Google search brings up lots of echo-effects
processors for guitars and such, but I found nothing for communication
usage. Do any readers here remember the device and its manufacturer
and how it worked?
I have a feeling it's another name for Lincompex, developed by the
British Post Office in 1966. Bell labs in the US apparently then came up
with something very similar - which I seem to remember was named
"Echoplex". Could be wrong - it was all a long time ago.....

Lincompex stands for LINKED COMPRESSOR and EXPANDER. The audio is
heavily compressed, and the pre-compression amplitude variations are
used to frequency modulate a 2900Hz control tone. This is combined with
the compressed audio (300-2700Hz) and fed to the TX. At the other end of
the circuit, the control tone is used by an expander to restore the
original amplitude variations.

Lincompex was used widely on international point to point SSB and ISB
voice circuits - and may still be in use (?)

The equipment was made by Marconi, and possibly ST&C (as was, before
Nortel bought them up).
Antonio Vernucci
2011-01-22 18:22:42 UTC
Permalink
You are both right.

On a 1966 issue of QST magazine, I found the advertisement of "Echoplex" by Kahn
Research Laboratories. It sold for more than 300$, which was not cheap at those
times.

As to Lincomplex, I remember a friend of mine working for Page Europe who told
me having installed Lincomplex on HF transmitters in Africa.

73

Tony I0JX
Rome Italy
Nordic Breeds WA4VZQ
2011-01-23 04:21:49 UTC
Permalink
Post by Antonio Vernucci
You are both right.
On a 1966 issue of QST magazine, I found the advertisement of
"Echoplex" by Kahn Research Laboratories. It sold for more than 300$,
which was not cheap at those times.
As to Lincomplex, I remember a friend of mine working for Page Europe
who told me having installed Lincomplex on HF transmitters in Africa.
73
Tony I0JX
Rome Italy
Thank you, Tony.

Somehow, I think you are talking about Leonard R. Kahn of Kahn Research
Laboratories in Freeport, Long Island, NY, and not A. Q. Khan of Khan
Research Laboratories in Kahuta, Pakistan (Pakistan's main nuclear
weapons laboratory as well as an emerging center for long-range missile
development). Leonard Kahn is best known for his paper: L.R. Kahn,
“Single Sideband Transmission by Envelope Elimination and Restoration,”
Proceedings of the IRE, Vol. 40, July 1952, pp. 803–806., and for his
work on AM stereo. Google somehow doesn't know the difference...

73, Barry WA4VZQ
coffelt2
2011-01-23 06:08:20 UTC
Permalink
Post by Nordic Breeds WA4VZQ
Post by Antonio Vernucci
You are both right.
On a 1966 issue of QST magazine, I found the advertisement of "Echoplex"
by Kahn Research Laboratories. It sold for more than 300$, which was not
cheap at those times.
As to Lincomplex, I remember a friend of mine working for Page Europe who
told me having installed Lincomplex on HF transmitters in Africa.
73
Tony I0JX
Rome Italy
Thank you, Tony.
Somehow, I think you are talking about Leonard R. Kahn of Kahn Research
Laboratories in Freeport, Long Island, NY, and not A. Q. Khan of Khan
Research Laboratories in Kahuta, Pakistan (Pakistan's main nuclear weapons
laboratory as well as an emerging center for long-range missile
development). Leonard Kahn is best known for his paper: L.R. Kahn,
“Single Sideband Transmission by Envelope Elimination and Restoration,”
Proceedings of the IRE, Vol. 40, July 1952, pp. 803–806., and for his work
on AM stereo. Google somehow doesn't know the difference...
73, Barry WA4VZQ
Wow, isn't this a super thread? Learned more here in a week of spare
time than 60 years of experiments and reading magazines! Where was
Usenet when we needed it?

Old Chief Lynn, W7LTQ
Antonio Vernucci
2011-01-23 09:22:29 UTC
Permalink
Post by Nordic Breeds WA4VZQ
Somehow, I think you are talking about Leonard R. Kahn of Kahn Research
Laboratories in Freeport, Long Island, NY, and not A. Q. Khan of Khan Research
Laboratories in Kahuta, Pakistan (Pakistan's main nuclear weapons laboratory
as well as an emerging center for long-range missile development). Leonard
Kahn is best known for his paper: L.R. Kahn, “Single Sideband Transmission by
Envelope Elimination and Restoration,” Proceedings of the IRE, Vol. 40, July
1952, pp. 803–806., and for his work on AM stereo. Google somehow doesn't
know the difference...
Yes, it was Leonard Kahn. I have an Kahn SSB adapter for 455-KHz IF receivers.
It employs a great deal of nuvistors. Very complex machine!

73

Tony I0JX
Alejandro Lieber
2011-03-07 15:47:21 UTC
Permalink
Post by Antonio Vernucci
I am planning to build a suppressor-grid modulated AM transmitter.
In all the diagrams I have seen they use proper pentodes, i.e. tubes
that have a real suppressor grid (e.g. 803).
I have seen no diagram using beam power tubes (e.g. 813 or 814) which
have beam forming plates instead of the suppressor grid .
Before purchasing 803 tubes, I would like to be sure that 813s or 814s
are really unsuitable for suppressor-grid modulation.
My question is whether, with 813s or 814s, the plate current can be
actually controlled by varying the beam forming plates voltage.
Does anyone have experience on that issue?
73
Tony I0JX
Rome, Italy
A little late, but could be of interest:

Try the 2E22 valve.

I used to work with this excellent valve during my military service in
1968, repairing military equipment that used it as supresor modulated.

It was built especially for that purpose.

Here are the specifications:

2E22
Power Pentode

Base & Bulb
EIA Base 5J

Mechanical Data

EIA Base ...................................... 5J
Electrical Data

Heater Voltage ................................ 6.3 V
Heater Current ................................ 1.5 A
Direct Interelectrode Capacitances (approx)

Pentode
Input ......................................... 13 pf
Output ........................................ 8 pf
Grid to Plate ................................. 0.2 pf
Maximum Ratings (Design Center Values)

Pentode
Plate Voltage ................................. 750 V
Grid No. 2 Voltage ............................ 250 V
Plate Dissipation ............................. 30 W
Grid No. 2 Dissipation ........................ 10 W
Characteristics and Typical Operation

Class C Oscillator/Amplifier
Plate Voltage ................................. 750 V
Grid No. 3 Voltage ............................ 22.5 V
Grid No. 2 Voltage ............................ 250 V
Grid No. 1 Voltage ............................ -60 V
Grid No. 1 Current ............................ 6 mA
Plate Current ................................. 100 mA
Grid No. 2 Current ............................ 16 mA
Driving Power ................................. 0.55 W
Power Output (approx) ......................... 53 W
Characteristics and Typical Operation

Class C Modulated Amplifier (Supressor)
Plate Voltage ................................. 750 V
Grid No. 3 Voltage ............................ -90 V
Grid No. 2 Voltage ............................ 250 V
Grid No. 1 Voltage ............................ -90 V
Plate Current ................................. 55 mA
Grid No. 2 Current ............................ 29 mA
Power Output (approx) ......................... 16.25 W

Alejandro Lieber
LU1FCR
Rosario - Argentina

Real-Time F2-Layer Critical Frequency Map foF2 at:

http://1fcr.com.ar
Antonio Vernucci
2011-03-09 23:31:38 UTC
Permalink
Post by Alejandro Lieber
Try the 2E22 valve.
I used to work with this excellent valve during my military service in 1968,
repairing military equipment that used it as supresor modulated.
Thanks for suggestion. I have some 2E22s, even some 2E24s (quick.heating
versions).

The problem with the 2E22 is that the output power would be small (probably 10W
or so) because, using suppressor screen modulation, the efficiency is rather low
(<30%).

Using two 803s I can instead get 200W or perhaps 250W of carrier.

73

Tony I0JX
Nordic Breeds WA4VZQ
2011-03-10 00:48:50 UTC
Permalink
Post by Antonio Vernucci
Thanks for suggestion. I have some 2E22s, even some 2E24s
(quick.heating versions).
The problem with the 2E22 is that the output power would be small
(probably 10W or so) because, using suppressor screen modulation, the
efficiency is rather low (<30%).
Using two 803s I can instead get 200W or perhaps 250W of carrier.
73
Tony I0JX
Hi Tony,

The 2E22 is a true pentode while the 2E24 is a quick heating filament
version of the 2E26. Both are beam power tetrodes and not suitable for
suppressor modulation. A pair of suppressor modulated 803's will deliver
approximately 100 watts of carrier.

73, Barry WA4VZQ
v***@orange.fr
2016-03-05 11:31:05 UTC
Permalink
Post by Nordic Breeds WA4VZQ
Hi Tony,
The 2E22 is a true pentode while the 2E24 is a quick heating filament
version of the 2E26. Both are beam power tetrodes and not suitable for
suppressor modulation. A pair of suppressor modulated 803's will deliver
approximately 100 watts of carrier.
73, Barry WA4VZQ
Hello,

Barry is right !

With 2 x 803, input power will be as far as 1,5 x 2 x 125 W = 375 W

and carrier power, about 125 W (33% of 375) only. No more !

All the best
Jean-Pierre (F6BGV)

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