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Subelement L07
Active Devices: Diodes, Transistors and Tubes.
Section L07
A circuit designed to increase the level of its input signal is called:
  • a receiver
  • Correct Answer
    an amplifier
  • a modulator
  • an oscillator

key word: INCREASE. An amplifier reproduces its input signal into a larger output signal ( more voltage, more current, more power).

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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If an amplifier becomes non-linear, the output signal would:
  • be saturated
  • cause oscillations
  • overload the power supply
  • Correct Answer
    become distorted

If an amplifier is 'linear', amplification, as a ratio of output versus input, will be constant regardless of frequency or amplitude of the input signal. Linearity is synonym with 'absence of distortion'. 'Non-linear' implies distortion.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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To increase the level of very weak radio signals from an antenna, you would use:
  • Correct Answer
    an RF amplifier
  • an RF oscillator
  • an audio oscillator
  • an audio amplifier

key words: INCREASE WEAK RADIO signals. A radio frequency (RF) amplifier must be used.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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To increase the level of very weak signals from a microphone you would use:
  • an RF amplifier
  • an audio oscillator
  • Correct Answer
    an audio amplifier
  • an RF oscillator

key words: INCREASE WEAK microphone signal. An 'audio amplifier'. Frequently called a 'speech amplifier' or 'microphone amplifier' for this particular application.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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The range of frequencies to be amplified by a speech amplifier is typically:
  • 300 to 1000 Hz
  • 40 to 40 000 Hz
  • Correct Answer
    300 to 3000 Hz
  • 3 to 300 Hz

Frequencies audible to humans range from 20 Hz to 20 000 Hz. Speech frequencies important for intelligibility in communications range from 300 Hz to 3000 Hz.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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Which of the following is not amplified by an amplifier?
  • Current
  • Power
  • Voltage
  • Correct Answer
    Resistance

key word: NOT. Amplifiers work on voltage, current and power.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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The increase in signal level by an amplifier is called:
  • modulation
  • Correct Answer
    gain
  • attenuation
  • amplitude

Gain (synonymous with amplification) is an increase in signal voltage/current/power. 'Attenuation' is a loss (opposite to gain). 'Amplitude' is the instantaneous value of a signal. 'Modulation' is the impression of a message onto another signal.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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A device with gain has the property of:
  • oscillation
  • modulation
  • Correct Answer
    amplification
  • attenuation

Gain and Amplification are synonymous. 'Attenuation' is a loss (opposite to gain). 'Oscillation' is the production of an Alternating Current (AC) signal. 'Modulation' is the impression of a message onto another signal.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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A device labelled "Gain = 10 dB" is likely to be an:
  • attenuator
  • oscillator
  • audio fader
  • Correct Answer
    amplifier

Gain and Amplification are synonymous. 'Attenuation' is a loss (opposite to gain). 'Oscillation' is the production of an Alternating Current (AC) signal. 'Modulation' is the impression of a message onto another signal.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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Amplifiers can amplify:
  • voltage, current, or inductance
  • Correct Answer
    voltage, current, or power
  • current, power, or inductance
  • voltage, power, or inductance

Recall that Inductance, a property of coils, is influenced by "The core material, the core diameter, the length of the coil and the number of turns of wire used to wind the coil".

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Which of the following is not a property of an amplifier?
  • Distortion
  • Correct Answer
    Loss
  • Gain
  • Linearity

key word: NOT. Gain and Amplification are synonymous. Linearity (or lack of distortion) is a specification of amplifiers. Loss has nothing to do with amplifiers.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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Zener diodes are used as:
  • RF detectors
  • AF detectors
  • Correct Answer
    voltage regulators
  • current regulators

ZENER diodes maintain a constant voltage across their terminals. Hence, they are used for voltage regulation.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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One important application for diodes is recovering information from transmitted signals. This is referred to as:
  • biasing
  • Correct Answer
    demodulation
  • regeneration
  • ionization

Detection = DEmodulation = Recovery of the message carried on a radio signal.

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The primary purpose of a Zener diode is to:
  • to boost the power supply voltage
  • provide a path through which current can flow
  • Correct Answer
    regulate or maintain a constant voltage
  • provide a voltage phase shift

ZENER diodes maintain a constant voltage across their terminals. Hence, they are used for voltage regulation.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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The action of changing alternating current to direct current is called:
  • amplification
  • transformation
  • modulation
  • Correct Answer
    rectification

Changing AC to DC is called 'Rectification'. AC is turned into 'pulsating DC' (it flows in one direction only) after going through a diode. In Power Supply circuits, diodes are called 'Rectifiers'. Diodes have two electrodes: Cathode and Anode. Electrons flow from Cathode to Anode in a forward-biased (i.e., a diode subjected to a voltage polarity which permits conduction) diode.

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The electrodes of a semiconductor diode are known as:
  • cathode and drain
  • Correct Answer
    anode and cathode
  • gate and source
  • collector and base

A DIODE, vacuum tube or semiconductor, has two electrodes: Anode and Cathode. Electrons flow from Cathode to Anode in a forward-biased (i.e., a diode subjected to a voltage polarity which permits conduction) diode. Cathode/Grid/Anode(plate) are electrodes in a vacuum triode. Source/Gate/Drain are electrodes in a Field Effect Transistor (FET, N-Channel or P-Channel). Emitter/Base/Collector are electrodes in a Bipolar Transistor ( type PNP or NPN ).

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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If alternating current is applied to the anode of a diode, what would you expect to see at the cathode?
  • No signal
  • Steady direct current
  • Pulsating alternating current
  • Correct Answer
    Pulsating direct current

Changing AC to DC is called 'Rectification'. AC is turned into 'pulsating DC' (it flows in one direction only) after going through a diode. In Power Supply circuits, diodes are called 'Rectifiers'. Diodes have two electrodes: Cathode and Anode. Electrons flow from Cathode to Anode in a forward-biased (i.e., a diode subjected to a voltage polarity which permits conduction) diode.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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In a semiconductor diode, electrons flow from:
  • grid to anode
  • Correct Answer
    cathode to anode
  • anode to cathode
  • cathode to grid

A DIODE, vacuum tube or semiconductor, has two electrodes: Anode and Cathode. Electrons flow from Cathode to Anode in a forward-biased (i.e., a diode subjected to a voltage polarity which permits conduction) diode. Cathode/Grid/Anode(plate) are electrodes in a vacuum triode. Source/Gate/Drain are electrodes in a Field Effect Transistor (FET, N-Channel or P-Channel). Emitter/Base/Collector are electrodes in a Bipolar Transistor ( type PNP or NPN ).

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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What semiconductor device glows different colours, depending upon its chemical composition?
  • A vacuum diode
  • Correct Answer
    A light-emitting diode
  • A fluorescent bulb
  • A neon bulb

key word: SEMI-CONDUCTOR. "LED", a Light-Emitting Diode.

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Voltage regulation is the principal application of the:
  • Correct Answer
    Zener diode
  • junction diode
  • light-emitting diode
  • vacuum diode

ZENER diodes maintain a constant voltage across their terminals. Hence, they are used for voltage regulation.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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In order for a diode to conduct, it must be:
  • enhanced
  • reverse-biased
  • Correct Answer
    forward-biased
  • close coupled

A DIODE, vacuum tube or semiconductor, has two electrodes: Anode and Cathode. Electrons flow from Cathode to Anode in a forward-biased (i.e., a diode subjected to a voltage polarity which permits conduction) diode. Cathode/Grid/Anode(plate) are electrodes in a vacuum triode. Source/Gate/Drain are electrodes in a Field Effect Transistor (FET, N-Channel or P-Channel). Emitter/Base/Collector are electrodes in a Bipolar Transistor ( type PNP or NPN ).

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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Which component can amplify a small signal using low voltages?
  • A multiple-cell battery
  • Correct Answer
    A PNP transistor
  • A variable resistor
  • An electrolytic capacitor

key words: AMPLIFY, LOW VOLTAGE. A transistor amplifies signals and can work at a low voltage. Bipolar Transistors ( type PNP or NPN ) as well as Field Effect Transistor (FET, N-Channel or P-Channel) can amplify signals.

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The basic semiconductor amplifying device is the:
  • Correct Answer
    transistor
  • tube
  • P-N junction
  • diode

key words: SEMICONDUCTOR, AMPLIFY. A transistor amplifies signals. Bipolar Transistors ( type PNP or NPN ) as well as Field Effect Transistor (FET, N-Channel or P-Channel) can amplify signals. A 'single P-N junction' is a diode. Diodes have two main uses: 'Rectification' and 'Detection'.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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The three leads from a PNP transistor are named:
  • drain, base and source
  • collector, source and drain
  • gate, source and drain
  • Correct Answer
    collector, emitter and base

Emitter/Base/Collector are electrodes in a Bipolar Transistor ( type PNP or NPN ). Source/Gate/Drain are electrodes in a Field Effect Transistor (FET, N-Channel or P-Channel). Cathode/Grid/Anode(plate) are electrodes in a vacuum triode.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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If a low level signal is placed at the input to a transistor, a higher level of signal is produced at the output lead. This effect is known as:
  • detection
  • modulation
  • rectification
  • Correct Answer
    amplification

Detection = DEmodulation = Recovery of the message carried on a radio signal. 'Modulation' is the impression of a message onto another signal. 'Rectification' turns AC into 'pulsating DC' (it flows in one direction only) after going through a diode.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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Bipolar transistors usually have:
  • 2 leads
  • 4 leads
  • Correct Answer
    3 leads
  • 1 lead

Emitter/Base/Collector are electrodes in a Bipolar Transistor ( type PNP or NPN ). Source/Gate/Drain are electrodes in a Field Effect Transistor (FET, N-Channel or P-Channel). Cathode/Grid/Anode(plate) are electrodes in a vacuum triode.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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A semiconductor is described as a "general purpose audio NPN device". This would be:
  • a triode
  • an audio detector
  • Correct Answer
    a bipolar transistor
  • a silicon diode

key word: NPN. The only choice in the group comprising a sandwich of N-semiconductor and P-semiconductor is the 'Bipolar Transistor'.

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The two basic types of bipolar transistors are:
  • diode and triode types
  • varicap and Zener types
  • P and N channel types
  • Correct Answer
    NPN and PNP types

key word: BIPOLAR TRANSISTOR. It is constructed with a sandwich of N-semiconductor and P-semiconductor: NPN or PNP type.

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A transistor can be destroyed in a circuit by:
  • saturation
  • cut-off
  • Correct Answer
    excessive heat
  • excessive light

Extreme operating temperatures can rapidly destroy transistors.

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In a bipolar transistor, the _____________ compares closest to the control grid of a triode vacuum tube.
  • Correct Answer
    base
  • emitter
  • source
  • collector

Comparing Triode/Bipolar Transistor/FET in terms of their RESPECTIVE electrodes: Origin of charge carriers = Cathode/Emitter/Source. Control electrode = Grid/Base/Gate. Destination of charge carriers = Anode(plate)/Collector/Drain.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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In a bipolar transistor, the _____________ compares closest to the plate of a triode vacuum tube.
  • gate
  • emitter
  • base
  • Correct Answer
    collector

Comparing Triode/Bipolar Transistor/FET in terms of their RESPECTIVE electrodes: Origin of charge carriers = Cathode/Emitter/Source. Control electrode = Grid/Base/Gate. Destination of charge carriers = Anode(plate)/Collector/Drain.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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In a bipolar transistor, the _____________ compares closest to the cathode of a triode vacuum tube.
  • collector
  • base
  • drain
  • Correct Answer
    emitter

Comparing Triode/Bipolar Transistor/FET in terms of their RESPECTIVE electrodes: Origin of charge carriers = Cathode/Emitter/Source. Control electrode = Grid/Base/Gate. Destination of charge carriers = Anode(plate)/Collector/Drain.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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The two basic types of field effect transistors (FET) are:
  • NPN and PNP
  • germanium and silicon
  • inductive and capacitive
  • Correct Answer
    N and P channel

In a field effect transistor, Source and Drain are the two extremities of a 'channel' made of a single semi-conductor type. NPN and PNP are the two types of BIPOLAR Transistors.

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A semiconductor having its leads labelled gate, drain, and source is best described as a:
  • Correct Answer
    field-effect transistor
  • gated transistor
  • bipolar transistor
  • silicon diode

Source/Gate/Drain are electrodes in a Field Effect Transistor (FET, N-Channel or P-Channel). Emitter/Base/Collector are electrodes in a Bipolar Transistor ( type PNP or NPN ). Cathode/Grid/Anode(plate) are electrodes in a vacuum triode.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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In a field effect transistor, the ___________ is the terminal that controls the conductance of the channel.
  • collector
  • Correct Answer
    gate
  • drain
  • source

Comparing Triode/Bipolar Transistor/FET in terms of their RESPECTIVE electrodes: Origin of charge carriers = Cathode/Emitter/Source. Control electrode = Grid/Base/Gate. Destination of charge carriers = Anode(plate)/Collector/Drain.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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In a field effect transistor, the ___________ is the terminal where the charge carriers enter the channel.
  • Correct Answer
    source
  • gate
  • drain
  • emitter

Comparing Triode/Bipolar Transistor/FET in terms of their RESPECTIVE electrodes: Origin of charge carriers = Cathode/Emitter/Source. Control electrode = Grid/Base/Gate. Destination of charge carriers = Anode(plate)/Collector/Drain.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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In a field effect transistor, the ___________ is the terminal where the charge carriers leave the channel.
  • source
  • gate
  • Correct Answer
    drain
  • collector

Comparing Triode/Bipolar Transistor/FET in terms of their RESPECTIVE electrodes: Origin of charge carriers = Cathode/Emitter/Source. Control electrode = Grid/Base/Gate. Destination of charge carriers = Anode(plate)/Collector/Drain.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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Which semiconductor device has characteristics most similar to a triode vacuum tube?
  • Zener diode
  • Bipolar transistor
  • Correct Answer
    Field effect transistor
  • Junction diode

The triode and the FET both rely on a reverse voltage on their control electrodes to affect the current through the device.

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The control element in the field effect transistor is the:
  • source
  • drain
  • base
  • Correct Answer
    gate

Comparing Triode/Bipolar Transistor/FET in terms of their RESPECTIVE electrodes: Origin of charge carriers = Cathode/Emitter/Source. Control electrode = Grid/Base/Gate. Destination of charge carriers = Anode(plate)/Collector/Drain.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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If you wish to reduce the current flowing in a field effect transistor, you could:
  • increase the forward bias voltage
  • increase the forward bias gain
  • Correct Answer
    increase the reverse bias voltage
  • decrease the reverse bias voltage

The triode and the FET both rely on a reverse voltage on their control electrodes to affect the current through the device.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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The source of a field effect transistor corresponds to the _______ of a bipolar transistor.
  • collector
  • Correct Answer
    emitter
  • base
  • drain

Comparing Triode/Bipolar Transistor/FET in terms of their RESPECTIVE electrodes: Origin of charge carriers = Cathode/Emitter/Source. Control electrode = Grid/Base/Gate. Destination of charge carriers = Anode(plate)/Collector/Drain.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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The drain of a field effect transistor corresponds to the _______ of a bipolar transistor.
  • emitter
  • Correct Answer
    collector
  • base
  • source

Comparing Triode/Bipolar Transistor/FET in terms of their RESPECTIVE electrodes: Origin of charge carriers = Cathode/Emitter/Source. Control electrode = Grid/Base/Gate. Destination of charge carriers = Anode(plate)/Collector/Drain.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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Which two elements in a field effect transistor exhibit fairly similar characteristics?
  • Source and gate
  • Gate and drain
  • Source and base
  • Correct Answer
    Source and drain

Source and Drain are the two ends of the same block of semiconductor material, the 'Channel'. Only the control electrode, the Gate, is made of the opposite type of material.

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What is one reason a triode vacuum tube might be used instead of a transistor in a circuit?
  • Correct Answer
    It may be able to handle higher power
  • It uses less current
  • It is much smaller
  • It uses lower voltages

Vacuum triodes are larger, use current just to heat the filament and require higher voltages than transistors BUT they remain simpler to use in HIGH-POWER amplifiers.

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Which component can amplify a small signal but must use high voltages?
  • An electrolytic capacitor
  • A multiple-cell battery
  • Correct Answer
    A vacuum tube
  • A transistor

key words: AMPLIFY, HIGH VOLTAGE. Vacuum tubes amplify signals but work at higher voltages than transistors (generally low-voltage devices).

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A feature common to triode tubes and transistors is that both:
  • convert electrical energy to radio waves
  • use heat to cause electron movement
  • Correct Answer
    can amplify signals
  • have electrons drifting through a vacuum

Only vacuum tubes use heat to facilitate electron movement within an envelope free of air.

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In a vacuum tube, the electrode that is operated with the highest positive potential is the _________.
  • filament (heater)
  • cathode
  • grid
  • Correct Answer
    plate

The 'Plate' (or Anode) attracts electrons with a high positive voltage. The Cathode emits electrons. The Grid encircles the Cathode and controls the flow of electrons.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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In a vacuum tube, the electrode that is usually a cylinder of wire mesh is the _______.
  • Correct Answer
    grid
  • filament (heater)
  • cathode
  • plate

The 'Grid' is a wire mesh (looking like a fence, so to speak) around the Cathode. The 'Plate' (or Anode) attracts electrons with a high positive voltage. The Cathode emits electrons. The Grid encircles the Cathode and controls the flow of electrons.

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In a vacuum tube, the element that is furthest away from the plate is the __________.
  • Correct Answer
    filament (heater)
  • grid
  • emitter
  • cathode

key words: ELEMENT, FURTHEST. A "directly-heated triode" comprises a filament (serving as a cathode, emitting electrons), a grid and a plate (or anode). An "indirectly-heated triode" comprises a heater (heating the cathode), a cathode (emitting electrons), a grid and a plate (or anode).

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In a vacuum tube, the electrode that emits electrons is the __________.
  • grid
  • collector
  • plate
  • Correct Answer
    cathode

The 'Plate' (or Anode) attracts electrons with a high positive voltage. The Cathode emits electrons. The Grid encircles the Cathode and controls the flow of electrons.

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What is inside the envelope of a triode tube?
  • Argon
  • Air
  • Neon
  • Correct Answer
    A vacuum

A 'vacuum' is the absence of air. Air is pumped out of vacuum tubes (like light bulbs) to prevent the filament from burning up.

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How many grids are there in a triode vacuum tube?
  • Three plus a filament
  • Correct Answer
    One
  • Two
  • Three

key words: GRID, TRIODE. A triode is a 3-electrode device: a cathode, a single GRID and a plate (or anode).

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