Agenda
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A brief history
Thermal emission
The diode
The triode
How do triodes amplify?
23/03/2013
RATS presentation 2013 Mike Maxey
G8CTJ
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In 1802, Humphrey Davy invents the electric lamp - 1
In 1875, American, G.R. Carey invents the phototube.
In 1878, Englishman Sir William Crookes invents the
Crookes tube - 2…
In 1895, German, Wilhelm Roengten invents an X-ray tube.
In 1897, German, Karl Ferdinand Braun invents the cathode
ray tube. - 5
In 1904, John Ambrose Fleming invents the first practical
valve called the 'Fleming Valve‘ / ‘Kenotron’. - 3
In 1906, Lee de Forest invents the Audion later called the
triode. - 4
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RATS presentation 2013 Mike Maxey
G8CTJ
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One of the most famous Crookes tubes.
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Demonstrates that electrons go in a straight line
and are stopped by metal, hence you see the
shadow of the cross on the end glass.
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After a while due to fatigue of the glass the glow is
weaker
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G8CTJ
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Important discoveries stemming from the Crookes tube.
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Wilhelm Röntgen discovered X-rays using the Crookes tube in
1895.
In 1897 J. J. Thomson identified “cathode rays” as negatively
charged particles, later renamed “electrons.”
Now Edison …
23/03/2013
RATS presentation 2013 Mike Maxey
G8CTJ
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Edison was facing a problem with his light bulbs due
to their short life.
Although the filament life was a problem, the major
limiting factor was that the bulbs quickly became
blackened.
Initially this was attributed to atoms of carbon from the
filament hitting the glass.
Despite this …
23/03/2013
RATS presentation 2013 Mike Maxey
G8CTJ
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1880 Edison patent
U.S. Patent #223898 issued to
Thomas Edison on January 27,
1880 for an incandescent lamp
Twenty-two other people also
devised versions of the light bulb,
Edison's outstrip the others
because
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Effective incandescent material,
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Higher vacuum
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High resistance made power
distribution from a centralized
source economically viable.
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Photos ….
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RATS presentation 2013 Mike Maxey
G8CTJ
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Very early Edison lamp
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Not very practical
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But some were attractive..
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The early lamps
were attractive but
very inefficient
Edison effect…
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Particles leaving the filament were known to be negatively
charged, so experiments were carried out to prevent them from
hitting the glass.
One method that Edison tried involved placing a second
electrode in the envelope.
He reasoned that if he placed a positive charge on the second
electrode, particles would be attracted away from hitting the glass
of the bulb.
Edison experimented with the polarity of the charge on the second
electrode and he noticed that when the second element was made
positive with respect to the filament a current flowed in the
circuit. When the potentials were reversed this did not happen.
This became known as the Edison effect. Used by Flemming…
23/03/2013
RATS presentation 2013 Mike Maxey
G8CTJ
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J.A. Fleming was a consultant to the Marconi
Coherers and Magnetic Detectors
In November 1904 whilst he was walking along Gower
Street in London’s West End he had what he called “a
very happy thought".
He wondered if the Edison Effect could be used to
rectify the "feeble to and fro motions of electricity
from an aerial wire".
Fleming set up an experiment and was able to prove
that the idea worked. Patented in 1905…
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RATS presentation 2013 Mike Maxey
G8CTJ
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Flemmings
Patent 1905
The Kenotron…
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Patent original
Others not so
attractive….
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G8CTJ
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Actual hand blown
Valves used in
Flemming’s 1904
Experiments
Then the first
practical diode…
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RATS presentation 2013 Mike Maxey
G8CTJ
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Actual diode valve Used by Marconi in 1904
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There are 3 types of electron Emission
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Secondary – High velocity particles – X rays
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Photo – Photons of light – photo cells
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Thermionic / Thermal Emission…
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RATS presentation 2013 Mike Maxey
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At ambient temperature outer shell electrons
have insufficient velocity to escape
As temperature increases the molecular
vibration increases
Rotational velocity increases
Electrons “Boil” off into surrounding space…
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G8CTJ
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Material
Tungsten
Thoriated Tungsten
Oxide coated
Normal Operating
Temperature
°K
2450 to 2600
Efficiency in
mA of emission
per watt heater
power
3 to 15
1900
62.5
1100 to 1170
50 to 125
All materials developed to produce maximum electron flow…
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RATS presentation 2013 Mike Maxey
G8CTJ
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Two requirements for electron flow
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Filament heated to
correct temperature to
achieve thermal emission
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Positive anode potential
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Require to plot curves…
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RATS presentation 2013 Mike Maxey
G8CTJ
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A dynamic curve must be
plotted to see how the diode
works. This requires :-
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A Fixed heater voltage
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A Variable Anode voltage
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We get an Ia /Va curve…
RATS presentation 2013 Mike Maxey
G8CTJ
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From this curve we
calculate the Ra….
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The workshop of Alfred Charles Cossor in
Clerkenwell London
Latter to become a leading British valve
manufacturer.
Photograph taken in 1896
Some of his workers (children!) preparing
glass tubes.
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Lee DE Forest
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1906 works to improve diode
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1908 patents at three electrode valve the
Audion…
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G8CTJ
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Early Audion
1906
Latter versions..
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The Audion valve
1908
The Grid…
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Fitted between heater and anode…
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Electrically it looks like…
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Like the diode we
need to plot some
curves….
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RATS presentation 2013 Mike Maxey
G8CTJ
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With this circuit we can
plot the Ia/Va and Ia/Vg
curves…
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Input voltage
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Output current
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RATS presentation 2013 Mike Maxey
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Input voltage
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Output current
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RATS presentation 2013 Mike Maxey
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Input voltage
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Output current
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To output voltage
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RATS presentation 2013 Mike Maxey
G8CTJ
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Directly heated – Battery powered sets
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Indirectly heated – Mains powered sets
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Directly heated specials – large rectifiers and
transmitting valves
23/03/2013
RATS presentation 2013 Mike Maxey
G8CTJ
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The R' valve (1922)
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The first widely used triode
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Note the thin wire filament
suspended inside helical wire
grid, inside tubular anode.
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RATS presentation 2013 Mike Maxey
G8CTJ
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Ediswan AR (1922)
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Cossor P2 (1922)
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Cosmos SP18 (1925)
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The Cossor device used an
unusual 'hat' construction to
avoid infringing patents
which specified tubular
electrodes.
RATS presentation 2013 Mike Maxey
G8CTJ
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