New-York tribune., 1922-05-07
Vacuum Tube
As Amplifier
And Detector
When Used as a Dctector II
Ac,s Like Valve in Water
system: Permits but Half
ofCurren,,oPass Through
7. Heart of Receiver
As Amplifer 1t Releases :, $,
Stored Up Energy Like
the Trigger of a Rife

the liiSS
-, -,resis Of the vacuum tube.
~. :. such an important factor in
-,3io receiving apparatus was described
!. .c article in this section last week
:, ,,;. story II is my intention TO dc
ser,bc just how 'Ae wonderful m
'..'s. .-,.,. .cts as detector and ampli-
Ser BY doing SO 1t might be we'll
;,, out ore Of the unusual ross'-
biIjties Of this instrument that Is now
,,c,yinr the attention Of scientists.
r.centIv was at demonstration Of
~. ~ these tubes producing alternat-
INC current Of any desired frequency
viT, = total output Of 10 kllowstts o.
ro.er. This means that III the very
,.,r future the vacuum tube will en-
,,.lv discard the bulky and cumber-
cone machinery now used for the pro
duet,on Of alternating current.
F.ed.bsck System Discovered
n the last article described the de-
v.loument Of the vacuum tube from the
I'm. tbst Edison first observed the ef
fec. Of its practical application by Pro
f,ssor Fleming; and finally, the add
ton OF the grid by DR. Lee dcForcst.
In TO this time We had vacuum tube,
but its possibilities were really un
known until Edwin II. Armstrong. q
Young American amateur, discovered
he feed back principles Of transform
M it from simple vacuum tube into
an electrical oscllator-a discovery
rheh has given to it al Of its re
markabe possibilities and made 1t
really and truly the modern Aladdins
lamp.
Now the manner in which the va
CUM tube functions as a detector is
as follows: As soon as the flamont
IS lighted, train OF electrons is
thrown of from the flament and these
lombard the plate. They arc in real
ty particles Of negatively charged
matter, which actually bombsrd the
plate with terrific impact, They az
ford path for negative electricity 10
pass between the flament aud the
plate and in order to assist the pas
sage Of this electricity the plate is
charged with positive potential The
grid enables US to control the action
Of the tube for this purpose.
When the incoming electro gnetic
waves pass over the aerial very
hlgh frequency alternating current is
ndUced in the oscillating circuit con-
nected with the aerial, which passes
thus current on 10 the vacuum tube.
he vacuum tube will only allow tho
negative half Of th,s alternating car
lent to pass through il. II completa-
y checks the positive half and there
lore acts as an electric valve IN ex-
aetIy the same way as the ordinary
valve operates in a wateY pipe system.
PulAtinE Current Works Phone
We -ave, therefore. on the other
SIDE OF the vacuum tube current of
t!ectriclty that Is q pulsating current
Sowing in one direction Only. and the
'elephone receiver * now able to re-
spond to 1t. That is the manner in
which the tubes acts AS detector.
As ar smplifer, a slightly different
condition exists and a different SC
TON takes place. In this case. We
rave what Is known ea a trigger cf-
'ect, and the action of the tube in
simplifying can be beat described bv
Using the trigger effect as an analogy
Ii YOU study the mechanism Of :
rIh. you viii realize that when yor
cock the gun you have 20 use .
great deal of force to pull the ham.
ner hack against the spring IN tn.
Eun. When you pull the hammer back
"hat you actually do is to store UP
'ertsin amount Of energy in tn,
spring Of the gun. which lies dorman
until such time is you bring it into
pay ~ pulling the trigger. A littlt
'housht viii show you how minute tn,
PRESSURE Is that YOU exert on the trlg
ger itself when firing the gun, but by
seessng the trigger YOU bring into
pay the larger amount Of energy that
- stored up IN the spring, ard this
-orces tho hammer against the cart.
.iose IN the gun with such force tha,
"e cartridge Is exploded This is ex-
"VIiy "hat the vacuum tube does
.tpn,Fo!s the larger amount Of energy
nay is stored up in the battery con
"ee'eo 10 the plate on the vacuum
.uOe "hen the weak. incoming cur
s"' reaches the grid or control ele.
reHl OF the tube, il releases this
,,v.eo.up ,,,.p energy by pulling the grid
''Esef and pernlittlnp ths nia.e an,