1873- Fredrick Guthrie, a British scientist
showed that a negatively charged iron ball would
lose its charge if heated to red hot
temperature. He also discovered that if the ball
was positively charged and heated to the same
temperatures it did not lose its charge.
1883- Edison experimented with ways to keep
the insides of incandescent light bulbs from
becoming blackened with carbon deposits that
originated at the filament. It was known that
the particles leaving the filament were
negatively charged. He placed a positively
charged element (anode) next to the filament and
this kept the bulbs from blackening. This effect
was then called the Edison Effect. A general way
to look at the Edison Effect is that negatively
charged particles leave the hot
filament(cathode) to a cold positively charged
electrode(anode).
Thomas Edison
Image Credit:
biography.com
1889- The British Engineer Ambrose Fleming
reproduced the Edison Effect. In 1904 he
experimented with how alternating current
electricity interacted with this “Edison Effect
Lamp”. He observed that only the top half of the
waveform passed through the lamp. Alternating
current was converted into pulsating direct
current. This was the first vacuum tube diode
and this circuit is called a rectifier. Though
rectifiers can be traced back before 1900, the
vacuum tube diode rectifier was the first purely
electronic one. Before that, rectifiers were
electromechanical devices.
Ambrose Fleming Image
Credit: www.smart90.com
1906-1911- The American Engineer Lee Deforest
developed the first triode vacuum tube. This
device could amplify weak signals. The triode
could also be used as an oscillator to produce a
pure sine wave. Many different triode
oscillators were developed and they brought
about the radio era of the 1920’s. Before that,
transmitters used mechanical spark gaps.
Lee Deforest
Image Credit: www.britannica.com
1915- The German Scientist Irving Langmuir
proved the idea that trace gases were needed
inside the tube to be incorrect. Later on, super
evacuated tubes were produced and they had much
better performance.
1920- RCA began commercial production of
vacuum tubes.
RCA Ads from the early
20th century.
Image Credits:
www.telegraph-office.com and
vintageadbrowser.com
1926- Tetrode tubes come about. The internal
capacitance between the grid and the anode was a
problem at high frequencies. Adding a second
grid solved that but secondary emission became a
problem. Pentodes came soon after by adding yet
another grid to combat secondary emission from
the screen grid to the control grid.
KT88 Audio Tetrode. The voltage present at the
anode was around 1250V.
Image Credit: www.flickr.com/photos/m0ukd/8074050008
Here is an RF Amp Pentode.
Image Credit: Oddmix.com
Many other tubes came about and they were
used just about everywhere there was
electricity.
Vacuum tube power supply used
in electrical discharge machining.
