Basic Vacuum Tube Glossary
This is a basic glossary of terms used in electron tube equipment. The
definitions are brief, and intended only to give the barest of descriptions.
The descriptions given are intended to be intuitive, rather than strictly
accurate. The author is aware that protons and neutrons are not truely
fundamental particles.
AC
Synonym for alternating current.
Informally used to refer to alternating
voltage.
Active Component
Active components are
components which have a connection to a source
of electrical power, and a
control electrode
which is used to control the flow of current
through them. Typical active components are
electron tubes, transistors, and
integrated circuits.
Alternating Current
Also called AC, electric current
which reverses direction periodically. This term is also sometimes used
informally for alternating voltage.
Alternating Voltage
Also called AC informally,
voltage which
reverses sign between (+) and (-) periodically.
AM
Synonym for amplitude modulation.
Amp
Abbreviation for ampere.
Ampere
The unit of electric current
(after André-Marie Ampère 1775-1836), representing a flow of
electric charge amounting to one
coulomb per second, often abbreviated
to amp.
Amplifier
An electronic circuit which takes
an electronic signal as an input,
and produces a replica with increased amplitude,
(voltage amplifier), current
(current amplifier), or power (power amplifier).
Amplitude
One of the four distinguishing characteristics of
periodic signals.
Amplitude Modulation
See modulation.
Atom
The basic unit of which pure elements are composed. They have a
compact and massive nucleus at the center which contains
protons bearing a (+) charge,
and neutrons which bear no charge. Electrons, which bear
a (-) charge, surround the nucleus. For more information
see Basic Tube Theory.
Audio Frequency
A frequency which lies within a range
considered audible to human beings. This is nominally the range of
20 Hz to 20,000 Hz, though few human beings can actually hear sounds
over that entire range.
Capacitance
Capacitance is the property of storing
energy in an
electric field.
Capacitor
A capacitor is a passive component
used to introduce a controlled amount of
capacitance into an
electronic circuit.
Cathode
A cathode is an electrode in an
electron tube used to emit
electrons into
the highly evacuated or gas filled interior of the tube. Cathodes
may be either heated or cold. Heated cathodes emit
electrons only when they are hot, and may be either directly
or indirectly heated. Cold cathodes emit electrons without
the necessity of being heated
A directly heated cathode is one which is heated by passing an
electric current through it, and
is called a filament. Any heated cathode which is not directly heated is
termed indirectly heated. Indirectly heated cathodes may be either
heated by a separate heater, in which case they are called unipotential
cathodes, or may be heated by other means, e.g. by ion bombardment
and eventual electronic current as used in the 0Z4 tube.
A cold cathode emits electrons, obtaining the energy necessary
to do so by means other than heat. Phototubes,
for example, use light energy to cause their cathodes to emit electrons.
For more information
see Basic Tube Theory.
Charge
As a noun, an abbreviation for electric
charge. As a verb, it means to remove or introduce
charged particles, thus producing
a net electric charge.
Charged Particle
Charged particles are particle which bear
electric charge and are subject to the
forces exerted by electric fields.
The two most important charged particles are the proton and the
electron. These two, along with the neutron, comprise atoms.
Circuit
Abbreviation for electronic circuit.
Cold Cathode
A cold cathode is a cathode which is not heated.
Component
Components are basic single units from which
electronic circuits, are constructed.
Components may be active or
passive.
Condenser
Synonym for capacitor.
Conductor
A substance or thing in which electrically charged
particles are relatively free to move, and which therefore
can carry an electric current.
Control Electrode
A control electrode is an electrode in an
active component used to control the
flow of current through the component.
Converter
A type of circuit which accepts as
an input a modulated
periodic signal and produces
as output a periodic signal at another frequency
having the same modulation characteristics as the input signal.
Coulomb
The unit of electric charge (after
Charles-Augustin de Coulomb 1736-1806), equivalent to the amount of charge
carried by 6.28 x 10^28 (62,800,000,000,000,000,000,000,000,000) electrons.
Current
Abbreviation for electric current.
DC
Synonym for direct current. Also used
informally to refer to a relatively constant voltage which does
not change sign between (+) and (-).
Demodulator
A circuit which recovers the impressed
intelligence from a modulated signal.
Detector
Synonym for demodulator.
Diode
An electron tube with two elements,
a cathode, and a plate.
most commonly used as rectifiers
and detectors.
Direct Current
Also called DC, a relatively constant
current which flows in one direction only.
Electric Charge
Unfortunately, we do not know what electic charge is. We do know that
it comes in two forms, (+) positive and (-) negative. The unit of
charge is the coulomb. For more information, see
Basic Tube Theory.
Electric Current
The motion of charged particles,
by convention from (+) to (-). Unfortunately, in
electronic circuits the moving particles
are electrons which bear a (-) charge, and
hence move in the direction opposite to conventional current. The unit
of current is the ampere. For more information see
Basic Tube Theory.
Electric Energy
Energy in the form of an
electric field, magnetic field,
or electric current.
Electric Field
An effect on the space surrounding charged
particles exerting forces on the particles, either attractive or
repulsive, depending upon their respective charges. We say that
like charges repel, and unlike charges attract. Creating a net electric
field in otherwise neutral matter requires moving charged particles
contrary to the electric force between them,
thus expending energy.
This energy gets stored in the field as
electric energy. For more information, see
Basic Tube Theory.
Electric Force
The force charged particles experience
when immersed in the electric field
of other charged particles.
Electric Potential
The effective height of the electric field
surrounding a charged particle.
By analogy with the gravitational force, we can picture electric
fields as similar to a landscape with hills (regions of positive
potential) and dales (regions of negative potential). The gravitational
force propels water away from hills and causes it to flow toward dales.
Likewise positively charged particles experience a
force which
propels them away from regions of positive potential and attracts
them to regions of negative potential, causing an
electric current to flow. Unfortunately for this
analogy, negatively charged particles, which make up common
electric current must be imagined
as flowing uphill, due to a mistake by Benjamin Franklin.
Electrode
An electrical conductor used to make contact with the
vacuum or low pressure gas in an electron tube.
Electron
One of the three fundamental particles comprising atoms.
Electron Tube
An electron tube is an evacuated chamber in which electrons flow
from an emitting electrode called the
cathode to one or more other electrodes.
Electron tubes may either be highly evacuated vacuum tubes, or filled
with a gas at low pressure.
For a brief description of how most vacuum tubes work, see
Basic Tube Theory.
Electronic Circuit
An arrangement of one or more
electronic components
through which an electric current flows.
Electronic Signal
An electric current
or voltage which is
varied in time
for the purpose of conveying information, such as voice, music, digital
data, etc.
Energy
The ability to do work. It takes various forms, as
the energy of motion (kinetic energy), the energy of heat
(thermal energy) or
electric energy.
Field
A condition in a region of space created by particles in or near
that region, and affecting some or all of the other particles
within that region. We think of forces as originating in fields
which emanate from the particles. The most commonly experienced
fields are the gravitational field, the
electric field, and the magnetic
field.
Filament
A filament is a directly heated cathode.
First Detector
Synonym for converter.
Fleming Valve
A high vacuum electron tube
diode used as a radio detector
invented in 1897 by John Fleming in England, and initiating the
electron tube era. They were called valves because
electric current could flow through them in only one direction.
Fleming's Experimental Valves
FM
Synonym for frequency modulation.
Frequency
One of the four distinguishing characteristics of
periodic signals.
Frequency Modulation
See modulation.
Grid
Short for control grid, a control
electrode in triodes or in
multigrid tubes used to control the current flowing between the
cathode and plate.
Multigrid tubes have other grids in addition to the control grid.
For more information
see Basic Tube Theory.
Heater
A heater is an element of an electron tube
which is used to heat an indirectly heated cathode.
Inductance
Inductance is the property of storing energy in a
magnetic field.
Inductor
An inductor is a passive component
used to introduce a controlled amount of inductance
into an electronic circuit.
Insulator
A substance or thing in which electrically charged
particles are tightly bound to a location, and which therefore
cannot carry an electric current.
Ion
An atom which has become
charged by losing or gaining one or
more electrons. See
Basic Tube Theory.
Magnetic Field
The magnetic effect on the space surrounding magnetic materials and
electric currents. Creating a magnetic
field using electric currents requires moving electrons against the
magnetic force they experience exerted by the increasing magnetic field, thus
requiring energy. Hence magnetic fields store
electric energy. This effect is used in inductors.
Modulator
A circuit which modulates a periodic signal.
Modulation
The act of modifying the amplitude,
frequency, or phase of a
periodic signal, producing a
modulated signal. While the resulting signal is no longer periodic,
it may be nearly so, and one still may speak of its amplitude,
frequency, and phase, in an average sense.
If the modulation affects the amplitude of the periodic signal,
we speak of amplitude modulation, or AM. If the modulation affects
the frequency of the periodic signal, we speak of frequency modulation,
or FM. If the modulation affects the phase of the periodic signal,
we speak of phase modulation, or PM.
The usual reason for modulating a signal is to convey a message,
or other form of intelligence, as music, voice, etc. The act of
recovering the impressed intelligence is
demodulation. The corresponding demodulator is often referred
to as a detector, and we speak of AM or amplitude detectors,
FM or frequency detectors, and PM or phase detectors.
Neutron
One of the three fundamental particles comprising atoms.
Passive Component
A passive component is a component which has
no control electrode. Typical
passive components include resistors,
capacitors, and inductors.
For more information see Introduction to Components (warning: 30 megabytes).
Ohm
The unit of resistance (after Georg Simon Ohm 1789-1854),
symbolized as Ω (greek upper case omega), in some vintage literature
as ω (greek lower case omega). One hundred feet of twenty gauge wire
or one foot of forty gauge wire each have a resistance of about one ohm.
See Ohm's Law.
Ohm's Law
A difference of potential of one volt produces
an electric current with intensity of
one ampere in a conductor
with a resistance of one ohm.
In symbols:
V = I x R
Where
V is the voltage in the circuit
I is the current in the circuit
R is the resistance in the circuit
Period
One of the four distinguishing characteristics of
periodic signals.
Periodic Signal
A signal which varies in time such
that at regular time intervals the signal repeats itself. The smallest
such time interval is called the period of the signal. The reciprocal
of the period is called the frequency of the signal, the unit of which
is the hertz (after Heinrich Rudolf Hertz 1857-1894), symbolized as Hz,
previously by the cycle per second (cps),
or even briefly as cycles. By convention, unvarying signals are
also considered periodic with infinite period and zero frequency.
The overall shape of a periodic signal during one period is called the
waveform. The measure of the strength of a periodic signal is called its
amplitude. The difference in time between the starting points of the periods of
two otherwise identical periodic signals is called the relative phase
of the signals. When the waveform of the signals is sinusoidal, the phase
is sometimes expressed in degrees.
Periodic signals can differ only in waveform, amplitude, period
(or equivalently frequency), and phase.
Phase
One of the four distinguishing characteristics of
periodic signals.
Phase Modulation
See modulation.
Photomultiplier
A type of phototube used
for seeing in low illumination environments, colloquially to "see in the
dark".
Phototube
An electron tube in which the energy supplied
to the electrons in the
cathode causing them to
be emitted into the chamber is supplied by light.
Plate
The most positive electrode in
diodes and triodes.
PM
Synonym for phase modulation.
Power
The rate of expenditure of energy.
The basic unit of power is the joule per second, or watt
(after James Prescott Joule 1818-1889 and Scottish engineer
James Watt 1736-1819, resp.).
In electronic circuits with only
resistors in them, the power converted to heat
may be calculated as
P = I x I x R = V x V / R
Where
P is the power dissipated (turned into heat)
I is the current in the circuit
V is the voltage in the circuit
R is the resistance in the circuit
Power Amplifier
An amplifier used to increase the power of
a signal, as for driving a speaker or
transmitting antenna.
Proton
One of the three fundamental particles comprising atoms.
Radio Frequency
A frequency which lies above a range
considered audible to human beings, i.e. greater than 20,000 Hz.
Rectifier
An electron tube used to convert
alternating current
into pulsed unidirectional current, which may then
be filtered into direct current.
Regulator
An electronic circuit which stabilizes
the voltage or current
provided as the output from another circuit, making it constant.
Resistance
The property of converting electric energy
into thermal energy (heat).
Resistor
An electronic component used to
insert a controlled amount of resistance
into an electronic circuit.
Second Detector
Synonym for demodulator.
Thermal Energy
Energy in an object due to the random motion
of the particles comprising it.
Triode
An electron tube with three active
electrodes, a cathode,
a grid, and a plate.
Used as amplifiers,
detectors, modulators etc.
For more information
see Basic Tube Theory.
Tube
Abbreviation for electron tube.
Unipotential Cathode
A unipotential cathode is a cathode which is indirectly
heated by a heater.
Vacuum Tube
A vacuum tube is a highly evacuated electron tube.
Valve
Synonym for electron tube
Volt
The unit of difference in electric potential,
symbolized as V (after Alessandro Giuseppe Antonio Anastasio Volta 1745-1827).
A standard flashlight cell produces a constant difference of
potential of about 1.5 V. See Ohm's Law.
Voltage
The difference in electric potential
between two points. It is measured in volts.
One of the four distinguishing characteristics of
periodic signals.