Since my earlier post (dealing with the question of what is peak evelope
power output in an AM transmitter), I've been doing more scrutinizing
of tube Ip/Vp characteristic curves. They are much more non-linear than
the impression you get from just looking at the curves. Also, it is rare
or almost non-existant to find Ip vs screen voltage!

Lets look at the venerable 833 (from my RCA TT-3 transmitting tube
manual). This is a KW input class C triode.

From the curve:
at zero grid volts, 1 kV on the plate gives 175 ma plate current
2 kV 500 ma
That's more than a doubling of Ip for a doubling of Vp

at minus 50 grid volts, 2 kV on the plate gives 50 ma plate current
4 kV 750 ma

looking in my RCA receiving tube manual (RC-20) I found for a 6FG6
a sharp cutoff tetrode that only at zero grid volts was there a near
linear relationship between plate current and plate voltage (meaning zero
current at zero voltage, and a straight line [which actually deviated
slightly from a straight line] with some slope. But at 100 v on plate,
current was 14 milliamps, at 200 v on the plate, plate current was 34
miliamps. Definitely NOT a linear relationship. For the 6EM7 a triode,
and at any of a wide range of grid voltages, plate current could be
doubled with only a 15-20% increase in plate voltage.

My thinking on all of this leads me to claim that anyone who can start
with a 100 watt carrier from an AM transmitter and make a few assumptions
about 100% modulation and come up with a _calculation_ of something like
400 watts of peak power and represent that as having something to do with
reality is pure conjecture.

If anyone wants to put an appropriate oscilloscope on the transmitter output
and measure the RF voltage of unmodulated carrier into an appropriate load
and then measure the peak RF voltage when the carrier is modulated, then
and only then do they have a reasonable _basis_ for making a claim about
peak (instantaneous) output power.

"Straydog" wrote in message
.com...

Since my earlier post (dealing with the question of what is peak evelope
power output in an AM transmitter), I've been doing more scrutinizing
of tube Ip/Vp characteristic curves. They are much more non-linear than
the impression you get from just looking at the curves. Also, it is rare
or almost non-existant to find Ip vs screen voltage!


Terman explains how high-level Class C modulation works
in Radio Engineering (1932 edition) on page 370.

Are you as dumb as you seem??

--

Clif
"Straydog" wrote in message
.com...

Since my earlier post (dealing with the question of what is peak evelope
power output in an AM transmitter), I've been doing more scrutinizing of
tube Ip/Vp characteristic curves. They are much more non-linear than the
impression you get from just looking at the curves. Also, it is rare or
almost non-existant to find Ip vs screen voltage!

Lets look at the venerable 833 (from my RCA TT-3 transmitting tube
manual). This is a KW input class C triode.

From the curve:
at zero grid volts, 1 kV on the plate gives 175 ma plate current
2 kV 500 ma
That's more than a doubling of Ip for a doubling of Vp

at minus 50 grid volts, 2 kV on the plate gives 50 ma plate current
4 kV 750 ma

looking in my RCA receiving tube manual (RC-20) I found for a 6FG6
a sharp cutoff tetrode that only at zero grid volts was there a near
linear relationship between plate current and plate voltage (meaning zero
current at zero voltage, and a straight line [which actually deviated
slightly from a straight line] with some slope. But at 100 v on plate,
current was 14 milliamps, at 200 v on the plate, plate current was 34
miliamps. Definitely NOT a linear relationship. For the 6EM7 a triode, and
at any of a wide range of grid voltages, plate current could be
doubled with only a 15-20% increase in plate voltage.

My thinking on all of this leads me to claim that anyone who can start
with a 100 watt carrier from an AM transmitter and make a few assumptions
about 100% modulation and come up with a _calculation_ of something like
400 watts of peak power and represent that as having something to do with
reality is pure conjecture.

If anyone wants to put an appropriate oscilloscope on the transmitter
output
and measure the RF voltage of unmodulated carrier into an appropriate load
and then measure the peak RF voltage when the carrier is modulated, then
and only then do they have a reasonable _basis_ for making a claim about
peak (instantaneous) output power.

On Wed, 25 Jan 2006 22:09:48 -0500, Straydog wrote:


Since my earlier post (dealing with the question of what is peak evelope
power output in an AM transmitter), I've been doing more scrutinizing
of tube Ip/Vp characteristic curves. They are much more non-linear than
the impression you get from just looking at the curves. Also, it is rare
or almost non-existant to find Ip vs screen voltage!

Lets look at the venerable 833 (from my RCA TT-3 transmitting tube
manual). This is a KW input class C triode.

From the curve:
at zero grid volts, 1 kV on the plate gives 175 ma plate current
2 kV 500 ma
That's more than a doubling of Ip for a doubling of Vp

at minus 50 grid volts, 2 kV on the plate gives 50 ma plate current
4 kV 750 ma

looking in my RCA receiving tube manual (RC-20) I found for a 6FG6
a sharp cutoff tetrode that only at zero grid volts was there a near
linear relationship between plate current and plate voltage (meaning zero
current at zero voltage, and a straight line [which actually deviated
slightly from a straight line] with some slope. But at 100 v on plate,
current was 14 milliamps, at 200 v on the plate, plate current was 34
miliamps. Definitely NOT a linear relationship. For the 6EM7 a triode,
and at any of a wide range of grid voltages, plate current could be
doubled with only a 15-20% increase in plate voltage.

My thinking on all of this leads me to claim that anyone who can start
with a 100 watt carrier from an AM transmitter and make a few assumptions
about 100% modulation and come up with a _calculation_ of something like
400 watts of peak power and represent that as having something to do with
reality is pure conjecture.

If anyone wants to put an appropriate oscilloscope on the transmitter output
and measure the RF voltage of unmodulated carrier into an appropriate load
and then measure the peak RF voltage when the carrier is modulated, then
and only then do they have a reasonable _basis_ for making a claim about
peak (instantaneous) output power.

You can't just look at static curves. Consider that with AM modulation
there is usually grid leak bias on the final tube being modulated.
This allows the grid voltage to somewhat follow the modulation and
helps smooth out the non-linearity in the plate.

If you have access to any of Termans books, as peter said, there is an
excellent section on how modulation works.
He in fact shows that "plate current follows plate voltage almost
exactly with modulation". His words.

He also says that "triodes have considerably less distortion than
screen grid tubes".

73
Gary K4FMX

On Wed, 25 Jan 2006 22:09:48 -0500, Straydog wrote:


Since my earlier post (dealing with the question of what is peak evelope
power output in an AM transmitter), I've been doing more scrutinizing
of tube Ip/Vp characteristic curves. They are much more non-linear than
the impression you get from just looking at the curves. Also, it is rare
or almost non-existant to find Ip vs screen voltage!

Lets look at the venerable 833 (from my RCA TT-3 transmitting tube
manual). This is a KW input class C triode.

From the curve:
at zero grid volts, 1 kV on the plate gives 175 ma plate current
2 kV 500 ma
That's more than a doubling of Ip for a doubling of Vp

at minus 50 grid volts, 2 kV on the plate gives 50 ma plate current
4 kV 750 ma

looking in my RCA receiving tube manual (RC-20) I found for a 6FG6
a sharp cutoff tetrode that only at zero grid volts was there a near
linear relationship between plate current and plate voltage (meaning zero
current at zero voltage, and a straight line [which actually deviated
slightly from a straight line] with some slope. But at 100 v on plate,
current was 14 milliamps, at 200 v on the plate, plate current was 34
miliamps. Definitely NOT a linear relationship. For the 6EM7 a triode,
and at any of a wide range of grid voltages, plate current could be
doubled with only a 15-20% increase in plate voltage.

My thinking on all of this leads me to claim that anyone who can start
with a 100 watt carrier from an AM transmitter and make a few assumptions
about 100% modulation and come up with a _calculation_ of something like
400 watts of peak power and represent that as having something to do with
reality is pure conjecture.

If anyone wants to put an appropriate oscilloscope on the transmitter output
and measure the RF voltage of unmodulated carrier into an appropriate load
and then measure the peak RF voltage when the carrier is modulated, then
and only then do they have a reasonable _basis_ for making a claim about
peak (instantaneous) output power.

Methinks you are way too hung up on the abtract theory of how linear
tubes are.

In practice the majority of AM transmitters rated at 100 watts of
carrier output are indeed putting out 400 watts PEP with 100%
modulation. As another poster pointed out, this is easily proved by
using an oscilloscope or with SOME Peak reading wattmeters.

The FCC certainly agrees with the 4:1 ratio. That's why when the
Amateur power levels permitted by the FCC in the USA were raised to
1500 watts output PEP, the net result was that users of A.M had to
REDUCE carrier power to approximately 375 watts output.

Many diehard AM'ers and even the ARRL vigorously protested this net
reduction of power for AM use.
As I remember the FCC grandfathered the old power limit of 1000 watts
DC input to the final amplifier for Am'ers but only did so for a
couple of years.

Back in the good old days, I used to run a Technical Materiel Corp
GPT-750 AM transmitter on 3885KHZ. I ran 1KW DC input on the plate
with 100% modualtion. That required a 500 watt modulator in the
transmitter. The pair of 4-400A's in the rig easily achieved a power
output of 800 watts under class C high level modulation.
Thus I was legally running 3200 watts PEP output power.
The power supply exceeded 3000 volts and was rated at 1.5 amps CCS,
easily achieving the peak power demands..

You are sort of beating a dead horse. this was extensively discussed
everywhere in Amateur circles about a decade ago.

Doug/WA1TUT

On Thu, 26 Jan 2006, Gary Schafer wrote:

On Wed, 25 Jan 2006 22:09:48 -0500, Straydog wrote:


Since my earlier post (dealing with the question of what is peak evelope
power output in an AM transmitter), I've been doing more scrutinizing
of tube Ip/Vp characteristic curves. They are much more non-linear than
the impression you get from just looking at the curves. Also, it is rare
or almost non-existant to find Ip vs screen voltage!

Lets look at the venerable 833 (from my RCA TT-3 transmitting tube
manual). This is a KW input class C triode.

From the curve:
at zero grid volts, 1 kV on the plate gives 175 ma plate current
2 kV 500 ma
That's more than a doubling of Ip for a doubling of Vp

at minus 50 grid volts, 2 kV on the plate gives 50 ma plate current
4 kV 750 ma

looking in my RCA receiving tube manual (RC-20) I found for a 6FG6
a sharp cutoff tetrode that only at zero grid volts was there a near
linear relationship between plate current and plate voltage (meaning zero
current at zero voltage, and a straight line [which actually deviated
slightly from a straight line] with some slope. But at 100 v on plate,
current was 14 milliamps, at 200 v on the plate, plate current was 34
miliamps. Definitely NOT a linear relationship. For the 6EM7 a triode,
and at any of a wide range of grid voltages, plate current could be
doubled with only a 15-20% increase in plate voltage.

My thinking on all of this leads me to claim that anyone who can start
with a 100 watt carrier from an AM transmitter and make a few assumptions
about 100% modulation and come up with a _calculation_ of something like
400 watts of peak power and represent that as having something to do with
reality is pure conjecture.

If anyone wants to put an appropriate oscilloscope on the transmitter output
and measure the RF voltage of unmodulated carrier into an appropriate load
and then measure the peak RF voltage when the carrier is modulated, then
and only then do they have a reasonable _basis_ for making a claim about
peak (instantaneous) output power.

You can't just look at static curves. Consider that with AM modulation
there is usually grid leak bias on the final tube being modulated.
This allows the grid voltage to somewhat follow the modulation and
helps smooth out the non-linearity in the plate.

This was discussed in the RCA transmitting tube manual, but it also
referenced the technical references which go into this in much more
detail. However, if you want to say "you can't just look at static curves"
then you also can't just say "doubling plate voltage also doubles plate
current" either.

If you have access to any of Termans books, as peter said, there is an
excellent section on how modulation works.
He in fact shows that "plate current follows plate voltage almost
exactly with modulation". His words.

He also says that "triodes have considerably less distortion than
screen grid tubes".

I will decline to check this but words and phrases like "almost exactly"
and "considerably less" are unquantitative.

73
Gary K4FMX

On Thu, 26 Jan 2006, Doug wrote:

On Wed, 25 Jan 2006 22:09:48 -0500, Straydog wrote:


Since my earlier post (dealing with the question of what is peak evelope
power output in an AM transmitter), I've been doing more scrutinizing
of tube Ip/Vp characteristic curves. They are much more non-linear than
the impression you get from just looking at the curves. Also, it is rare
or almost non-existant to find Ip vs screen voltage!

Lets look at the venerable 833 (from my RCA TT-3 transmitting tube
manual). This is a KW input class C triode.

From the curve:
at zero grid volts, 1 kV on the plate gives 175 ma plate current
2 kV 500 ma
That's more than a doubling of Ip for a doubling of Vp

at minus 50 grid volts, 2 kV on the plate gives 50 ma plate current
4 kV 750 ma

looking in my RCA receiving tube manual (RC-20) I found for a 6FG6
a sharp cutoff tetrode that only at zero grid volts was there a near
linear relationship between plate current and plate voltage (meaning zero
current at zero voltage, and a straight line [which actually deviated
slightly from a straight line] with some slope. But at 100 v on plate,
current was 14 milliamps, at 200 v on the plate, plate current was 34
miliamps. Definitely NOT a linear relationship. For the 6EM7 a triode,
and at any of a wide range of grid voltages, plate current could be
doubled with only a 15-20% increase in plate voltage.

My thinking on all of this leads me to claim that anyone who can start
with a 100 watt carrier from an AM transmitter and make a few assumptions
about 100% modulation and come up with a _calculation_ of something like
400 watts of peak power and represent that as having something to do with
reality is pure conjecture.

If anyone wants to put an appropriate oscilloscope on the transmitter output
and measure the RF voltage of unmodulated carrier into an appropriate load
and then measure the peak RF voltage when the carrier is modulated, then
and only then do they have a reasonable _basis_ for making a claim about
peak (instantaneous) output power.

Methinks you are way too hung up on the abtract theory of how linear
tubes are.

In practice the majority of AM transmitters rated at 100 watts of
carrier output are indeed putting out 400 watts PEP with 100%
modulation. As another poster pointed out, this is easily proved by
using an oscilloscope or with SOME Peak reading wattmeters.

Well, I'll buy into the scope measurement.

I'll also buy into my prior incomplete understanding of Ip vs Vp
relationships when the tube curves are looked at without realizing that
screens have to be modulated as well as plates.

I don't like wattmeters (with mechanical needles) that claim to indicate
peak watts or have peak watt scales. But, that is my prejudice.

The FCC certainly agrees with the 4:1 ratio. That's why when the
Amateur power levels permitted by the FCC in the USA were raised to
1500 watts output PEP, the net result was that users of A.M had to
REDUCE carrier power to approximately 375 watts output.

I remember some of that. But at that time I was an SSB user only.

Many diehard AM'ers and even the ARRL vigorously protested this net
reduction of power for AM use.
As I remember the FCC grandfathered the old power limit of 1000 watts
DC input to the final amplifier for Am'ers but only did so for a
couple of years.

Back in the good old days, I used to run a Technical Materiel Corp
GPT-750 AM transmitter on 3885KHZ. I ran 1KW DC input on the plate
with 100% modualtion. That required a 500 watt modulator in the
transmitter. The pair of 4-400A's in the rig easily achieved a power
output of 800 watts under class C high level modulation.
Thus I was legally running 3200 watts PEP output power.
The power supply exceeded 3000 volts and was rated at 1.5 amps CCS,
easily achieving the peak power demands..

And what do you do now? If you don't mind me taking a little more of your
time. And, what about all these guys I hear on AM (160 & 75) who say they
are running Johnson "Desks" at 1 kW input, and modified former AM
broadcast transmitters with 833s in the final?

You are sort of beating a dead horse. this was extensively discussed
everywhere in Amateur circles about a decade ago.

A decade ago I was not interested in anything AM. A decade ago I had
nothing that would even come close to putting out any power that would
have even made me have to think about this FCC specification. Recently,
out of pure nostalgia, I partly restored a very chopped up Johnson Ranger
and got it back on the air, on AM, to my considerable delight. Otherwise
it was too chopped up for a full restoration (to include CW). Similarly,
lots of things I was interested in a decade ago, I'm not interested in
any more. And, I spend much more time at the bench now than at the
microphone.

Art, W4PON

Doug/WA1TUT

On Thu, 26 Jan 2006 19:31:08 -0500, Straydog wrote:



On Thu, 26 Jan 2006, Gary Schafer wrote:

On Wed, 25 Jan 2006 22:09:48 -0500, Straydog wrote:


Since my earlier post (dealing with the question of what is peak evelope
power output in an AM transmitter), I've been doing more scrutinizing
of tube Ip/Vp characteristic curves. They are much more non-linear than
the impression you get from just looking at the curves. Also, it is rare
or almost non-existant to find Ip vs screen voltage!

Lets look at the venerable 833 (from my RCA TT-3 transmitting tube
manual). This is a KW input class C triode.

From the curve:
at zero grid volts, 1 kV on the plate gives 175 ma plate current
2 kV 500 ma
That's more than a doubling of Ip for a doubling of Vp

at minus 50 grid volts, 2 kV on the plate gives 50 ma plate current
4 kV 750 ma

looking in my RCA receiving tube manual (RC-20) I found for a 6FG6
a sharp cutoff tetrode that only at zero grid volts was there a near
linear relationship between plate current and plate voltage (meaning zero
current at zero voltage, and a straight line [which actually deviated
slightly from a straight line] with some slope. But at 100 v on plate,
current was 14 milliamps, at 200 v on the plate, plate current was 34
miliamps. Definitely NOT a linear relationship. For the 6EM7 a triode,
and at any of a wide range of grid voltages, plate current could be
doubled with only a 15-20% increase in plate voltage.

My thinking on all of this leads me to claim that anyone who can start
with a 100 watt carrier from an AM transmitter and make a few assumptions
about 100% modulation and come up with a _calculation_ of something like
400 watts of peak power and represent that as having something to do with
reality is pure conjecture.

If anyone wants to put an appropriate oscilloscope on the transmitter output
and measure the RF voltage of unmodulated carrier into an appropriate load
and then measure the peak RF voltage when the carrier is modulated, then
and only then do they have a reasonable _basis_ for making a claim about
peak (instantaneous) output power.

You can't just look at static curves. Consider that with AM modulation
there is usually grid leak bias on the final tube being modulated.
This allows the grid voltage to somewhat follow the modulation and
helps smooth out the non-linearity in the plate.

This was discussed in the RCA transmitting tube manual, but it also
referenced the technical references which go into this in much more
detail. However, if you want to say "you can't just look at static curves"
then you also can't just say "doubling plate voltage also doubles plate
current" either.

If you have access to any of Termans books, as peter said, there is an
excellent section on how modulation works.
He in fact shows that "plate current follows plate voltage almost
exactly with modulation". His words.

He also says that "triodes have considerably less distortion than
screen grid tubes".

I will decline to check this but words and phrases like "almost exactly"
and "considerably less" are unquantitative.

Do you even know who Terman is?
I would doubt that you do or you would not make statements like that.
As a matter of fact if you had read any of his work you would not be
making most of the statements that you are in these threads.

At first I thought that you were interested in learning but I see you
would rather argue for the sake of arguing.

73
Gary K4FMX


73
Gary K4FMX

"Straydog" wrote in message
.com...


looking in my RCA receiving tube manual (RC-20) I found for a 6FG6
a sharp cutoff tetrode that only at zero grid volts was there a near
linear relationship between plate current and plate voltage (meaning zero
current at zero voltage, and a straight line [which actually deviated
slightly from a straight line] with some slope. But at 100 v on plate,
current was 14 milliamps, at 200 v on the plate, plate current was 34
miliamps. Definitely NOT a linear relationship. For the 6EM7 a triode,
and at any of a wide range of grid voltages, plate current could be
doubled with only a 15-20% increase in plate voltage.

My thinking on all of this leads me to claim that anyone who can start
with a 100 watt carrier from an AM transmitter and make a few assumptions
about 100% modulation and come up with a _calculation_ of something like
400 watts of peak power and represent that as having something to do with
reality is pure conjecture.



In some cases it is a lot easier to accept what is technically correct, and
work backwards to correct erroneous conclusions.

First, a Class C amplifier is driven into grid conduction, almost to the
point of plate saturation.

High Level AM modulation is applied to the SCREEN and PLATE,
only doubling the plate voltage as in your 6F6 example to show
a non linear relationship isn't a valid argument. What is the
operating Class of the tube, and did you account for the modulating
voltage also being applied to the screen grid?

To quote Henny: "A linear relation must exist between plate voltage
and tank circuit current for good operation... In such a modulated
amplifier, the output peak will be four times the unmodulated
carrier and the continuous power output with complete modulation
is 1.5 times the power at zero modulation." Note that is only
true for a true Class C power amplifier stage, and not for
Class A or B.

I doubt that Henny or Tenny based their texts on conjecture or
misguided realities.

Pete

" Uncle Peter" wrote in message
news:cufCf.16380$bF.7979@dukeread07...
I doubt that Henny or Tenny based their texts on conjecture or
misguided realities.

Pete



Henny or Terman!! Arggh! Typo.