It was unsoldered from an old CRT TV.
It is in a ceramic case. Lead spacing is 0.2" = 5.08 mm.
Many have a lead at each end. In either case, the element is held in place by cement.
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Resistors oppose the flow of current in any circuit, including a DC circuit. Inductors oppose current flow in an AC circuit, increasing with the frequency. While it is true that if you put an inductor in a DC circuit, and then apply power, the current will not raise instantly as it would without it. However, the question relates to the steady state, and once this occurs, the inductor has no influence.
| A 470 Ω wire-wound power resistor, rated 3 watts; J meaning 5% tolerance. It was unsoldered from an old CRT TV. It is in a ceramic case. Lead spacing is 0.2" = 5.08 mm. Many have a lead at each end. In either case, the element is held in place by cement. |
A potentiometer is a specific kind of variable resistor, often used as a volume control. They can also be used for setting many parameters, such as squelch level, RF gain, power output, and even DSP filter settings. In some cases the voltage from the pots on modern radios would be digitised to then set, the parameter, such as the bandwidth of the DSP filters. Real oscilloscopes also use several to position the trace, and set its brightness.
 | A dual, or stereo potentiometer, or "pot". On each level a track of carbon runs around from the terminal on the left (front of shot) to the right (rear). The centre terminal connects to the wiper. As the knob connected to the ¼" shaft is turned from anti-clockwise to clockwise, the resistance from it to the left terminal increases, and to the right one decreases. It is typically mounted to the front panel of the device via the threaded tube. |
A capacitor stores energy in the electric field in the insulating layer or air between the plates. They are also handy, as they can pass an AC (audio or RF) signal while blocking DC, and so are often used between stages of an amplifier.
 | A "super-capacitor" / "ultra-capacitor" often used for memory back-up. The standard electrolytic capacitor beside it is 470 μF, 40 volts. The minus signs indicate the negative terminal. Size of electrolytics range from a few millimetres in height or diameter, to the size of a can of beans, sometimes bigger, with termination via screw terminals and eyelets. |
 | Three metallised polyester capacitors, marked 100nJ100, meaning 100 nF, 5%, 100 volts. Here they are on the paper bandolier tape, used in automatic "pick-and-place" machines. A fairly wide range of values are supplied in this standard size. |
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| From left to right: A smallish ceramic, 104 meaning 100,000 pF (100 nF), K = 10%; a polyester, usually green, and so called a "greencap", also 100 nF, or 0.1 μF, J = 5%; a coated ceramic of 2200 pF (2.2 nF) at 2000 volts 10%; oops, this is a zinc oxide varistor, also called a MOV, which shorts out voltage spikes, this one clamping at 560 volts, but they do have some capacitance; and another coated ceramic, perhaps 1000 pF (marked on rear), rated for filtering in mains circuits. I photographed these before reading the values, hence the metal oxide varistor. MOVs tend to be blue, but capacitors come in this colour too. As you age you will need magnifiers to read the values... |
You can see some green "greencaps" on the Wiltronics site.
Not on the exam, Tantalum is used in polarised capacitors, and makes compact capacitors in the 0.1 to 100 μF range, for 6 to 35 volt ratings. While they have been replaced by low-leakage electrolytics in many applications; they are popular with mobile 'phone makers, and tantalite (aka Coltan) sourced from countries such as Rwanda and DR Congo is the subject of wars to access it, and is also used to fund wars.
An inductor stores energy in a magnetic field, within the coil of wire they are normally made from. They are also used when you want to pass DC or low frequency (AC) power into a feed-line, or extract it to run a pre-amplifier at the the top of your mast, while blocking RF from entering the power supply. Spiralled traces on a printed circuit board can also be used as an inductor.
Note that all wires and traces have some inductance, as well as capacitance to other conductors, including ground.
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| An inductor showing the wire coil, wrapped over an iron powder core. The value is 10 microhenries, and the current rating is 3 amps. The DC resistance is 77mΩ. The core is 18 mm long. Components with a lead at each end is termed "axial", as it appears to run through its axis. |
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| Another inductor showing the wire coil, also "pulled" from a CRT TV. The spacing of the "radial" leads is 0.2", or 5.08 mm. |
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| Nope, not a resistor; the turquoise case, and the plumpness are the two indicators this is a small inductor or "choke". Reading left to right, the 1 and 0 are values, with 1 additional 0, so 100 μH, or 100 microhenries. Silver indicates 10% tolerance. |
The simplest semiconductor device is the diode, which allows current to flow from the plain end to the banded one, but not in reverse. Flow is Anode (A) to Cathode (K). When current flows, there is a voltage drop, 0.6 to 0.7 volts for silicon. Multiplying this by the current, means that there is a loss of energy, which is converted to heat. In a rectifier bridge, the duty cycle is however less than 50%.
Not shown, surface mount components can be tiny. Typical resistors might be 1206 or 0805, meaning 0.12" x 0.06" or 0.08" x 0.05" (3.2 x 1.5mm, or 2.0 x 1.2mm), some even smaller. ICs with 0.05" (1.27mm) pin pitch can be soldered by hand, if careful; but there are finer pitch devices. SOT-23 transistors have a pin spacing of 1.9mm, some devices smaller.
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| The diode in the insulated TO-220 style (or ITO-220) package is rated at 8 amps. This is designed to be screwed to a heatsink. The RGP300 device in the DO-27 package is rated at 3 Amps. The 1N4004 in the DO-41 package is rated at 1 Amp. These are designed for use as rectifiers in various power supplies, or to prevent reverse current flow, say from a battery to a solar panel in darkness. Like many higher current devices, the SB880F is a Schottky diode, with a lower forward voltage drop, and thus lower heat dissipation. At the bottom is the 1N4148 signal diode in the glass DO-35 package is rated at 300 mA, but is used for things like diode logic. In each case power flows right to left, or bottom to top, the band being the cathode. Small Zener diodes are similar in appearance to the axial devices. |
The standard transistor, also called a bipolar junction transistor (BJT), consists of three layers of semiconductor material, usually silicon these days, but germanium in the past, or a few special applications. The exams just calls these a "transistor". Transistors require current to flow into (or from) the Base to operate, up to a twentieth of the collector to emitter current used to operate the load.
 | The transistor (left) is a BC548B NPN bipolar transistor, in this case made by Motorola. It can switch a small load, such as an LED or small lamp, or work as a low-power amplifier. The LM78L05ACZ (right) is a low power positive regulator, a shrunken version of the 7805. Both are in the TO-92 package. The leads are spaced 0.05". The outer leads can be dog-legged to fit a 0.1" board, or the centre lead dog-legged back to form a triangle. For production it is possible to purchase devices bent in either format. |
The transistors ability to amplify is called its gain. Within a single part-number this an vary over a wide range.
In the FET, or field effect transistor, conventional current flows from drain to source (note electrons flow the other way). Voltage on the gate controls the current flow. These are also called unipolar transistors. Gate current is super-low (often picoamps).
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| The transistor (left) in the insulated TO-220 (ITO-220) package is an SSS6N60 N-Channel MOSFET, a form of Field Effect transistor, screwed to a heatsink. Next to it is a voltage regulator, riveted to a smaller heatsink. The MC7912CT, or just 7912 is a negative version of the popular 78xx voltage regulator, the 12 indicating 12 volts. It is rated at 1 Amp, subject to heat dissipation. The MC and stylised M in the circle indicate it is from Motorola (now ON Semiconductor). In both cases each lead is spaced 0.1" between centres. | |
Off the exams, but perhaps handy to know if buying parts, resistors, capacitors, and inductors are termed "passive" components, or "passives". Those with an input which influences current flow in other parts are termed "active" components, including all classes of transistors, and ICs. You will notice that the latter are semiconductors, but valves are also active devices. Diodes vary in their classification.
Unless defined otherwise, a switch is a mechanical device with physically connects or disconnects the circuit. The big old knife switches in Frankenstein style movies demonstrate this. There are toggle, rocker, slide, "piano key", rotary, and push-button ones; some with momentary action (they spring-back when released). Some have a locking mechanism, to prevent accidental operation, without say, pulling the toggle. The simplest is the SPST - single pole, single throw, meaning a single circuit, with only an on-off function, and just two terminals.
There are two families of batteries, non-rechargeable (consisting of primary cells) and rechargeable (consisting of secondary cells).
The non-rechargeable in the exam is the carbon-zinc, the standard 1.5 volt cell, actually somewhat rare. An improved version, containing chloride in the electrolyte sold as "heavy-duty" or "extra heavy-duty", or "super heavy-duty". Despite the spin, these have considerably less capacity than the alkaline or "alkaline-manganese" battery. In the carbon-zinc, the case is the zinc negative electrode, and the acid electrolyte eats away the case as the battery is used, and if they are left in a device for an extended period, with corrode through, and damage the device. Alkaline is much more suitable for using in AA cell cases available for some HTs. Off the exam, some radios use lithium coin cells (3 volt), or silver-oxide cells, to maintain the memory.
Used cells should be placed in the bins at Aldi, as the metals, especially zinc, should not go to landfill. (Provision of the bins in a requirement in the EU).
Rechargeable: Motor vehicles use lead-acid batteries to start the car, and to operate accessories when the ignition is off, and so the alternator is not running. These also smooth the pulsing or rippled DC from the alternator. Standard automotive batteries are not suitable for running equipment for extended periods; but "deep cycle" and some marine batteries are. Lead-acid gel-cell (also called AGM) is a variation, handy for mountain-top operating.
Nickel-cadmium and Nickel-metal hydride are often in dry-cell formats, or in battery-packs in older hand-helds. There are also liquid Ni-Cad batteries, which can last many decades if looked after.
A more recent addition is the Lithium-ion cell, used as single cells in pocket sized HTs, and as two cell batteries in larger models. 14.4 volt four cell ones, designed for RC uses, are also being used by the Summits-on-the-Air brigade to power 12 volts radios.
Often enclosed in glass, ceramic, or plastic, fuses consist of a thin wire, or stamped sheet metal, which melts or vaporises when an excessive current flows through it. A mirrored glaze inside the glass means the fuses end was the result of a serious short or surge; small balls at the ends of the remaining wires means a much less serious overload.
Both batteries and fuses are further discussed in the Safety section.
These are the actual questions relating to the information above.
T6A01
What electrical component is used to oppose the flow of current in a DC circuit?
A. Inductor
B. Resistor
C. Voltmeter
D. Transformer
In a steady-state DC circuit only a resistor opposes (or reduces) current flow, so circle answer B.
T6A02
What type of component is often used as an adjustable volume control?
A. Fixed resistor
B. Power resistor
C. Potentiometer
D. Transformer
This is the "Pot", or potentiometer, answer C.
T6A03
What electrical parameter is controlled by a potentiometer?
A. Inductance
B. Resistance
C. Capacitance
D. Field strength
While it may affect another real world function, the electrical parameter is resistance, answer B.
T6A04
What electrical component stores energy in an electric field?
A. Resistor
B. Capacitor
C. Inductor
D. Diode
This is the capacitor, answer B. Capacitors store energy in an insulator, and it is insulators which are usually involved in static electricity, like plastics, rubber, dry wool, and artificial fabrics (plastics).
T6A05
What type of electrical component consists of two or more conductive surfaces separated by an insulator?
A. Resistor
B. Potentiometer
C. Oscillator
D. Capacitor
The symbol for a capacitor is two plates with an air-gap insulator, so answer D. We pysically see these plates in the large old tuning capacitors, also used in some antenna tuners.
T6A06
What type of electrical component stores energy in a magnetic field?
A. Resistor
B. Capacitor
C. Inductor
D. Diode
This is the inductor, answer C. An inductor is a coil, and we relate coils to electro-magnets.
T6A07
What electrical component is usually composed of a coil of wire?
A. Switch
B. Capacitor
C. Diode
D. Inductor
The symbol for the inductor looks like a coil of wire, answer D.
T6A08
What electrical component is used to connect or disconnect electrical circuits?
A. Magnetron
B. Switch
C. Thermistor
D. All of these choices are correct
A switch physically connects or disconnects the circuit, answer D.
T6A09
What electrical component is used to protect other circuit components from current overloads?
A. Fuse
B. Capacitor
C. Inductor
D. All of these choices are correct
A fuse "blows", or goes open-circuit when excessive, potentially damaging, current flows, answer A.
T6A10
Which of the following battery types is rechargeable?
A. Nickel-metal hydride
B. Lithium-ion
C. Lead-acid gel-cell
D. All of these choices are correct
All are rechargeable, and have application in Ham radio, so answer D.
T6A11
Which of the following battery types is not rechargeable?
A. Nickel-cadmium
B. Carbon-zinc
C. Lead-acid
D. Lithium-ion
Þe aulde Carbon-zinc, usually sold as "Heavy Duty", is non-rechargeable, also called a "primary cell". Answer B gets you the Banana!
T6B01
What class of electronic components is capable of using a voltage or current signal to control current flow?
A. Capacitors
B. Inductors
C. Resistors
D. Transistors
Current (driven by a voltage) going into the Base of a transistor allows current to flow from Collector to Emitter, answer D. (Note the flow is reverse in PNPs.)
T6B02
What electronic component allows current to flow in only one direction?
A. Resistor
B. Fuse
C. Diode
D. Driven Element
This is the diode, answer C. --|>|--
T6B03
Which of these components can be used as an electronic switch or amplifier?
A. Oscillator
B. Potentiometer
C. Transistor
D. Voltmeter
The only applicable device here is the Transistor, answer C. Note that an oscillator is a multi-component device.
T6B04
Which of the following components can be made of three layers of semiconductor material?
A. Alternator
B. Transistor
C. Triode
D. Pentagrid converter
This is the transistor, the only solid state device here, answer B. The lower two are thermionic valves / electron tubes. The first is the generator in your (modern) car.
T6B05
Which of the following electronic components can amplify signals?
A. Transistor
B. Variable resistor
C. Electrolytic capacitor
D. Multi-cell battery
The transistor is the only amplifying device listed here, so answer A.
T6B06
How is the cathode lead of a semiconductor diode usually identified?
A. With the word cathode
B. With a stripe
C. With the letter C
D. All of these choices are correct
A diode's cathode is are most usually identified with a band, matching the bar on the symbol, answer B. Where a letter is used, and this is rare, it is K.
T6B07
What does the abbreviation LED stand for?
A. Low Emission Diode
B. Light Emitting Diode
C. Liquid Emission Detector
D. Long Echo Delay
It is a diode which emits light, so answer B, light emitting diode. The rest are silly.
T6B08
What does the abbreviation FET stand for?
A. Field Effect Transistor
B. Fast Electron Transistor
C. Free Electron Transition
D. Field Emission Thickness
It is the Field Effect Transistor, answer A. The rest of the terms are nutty.
T6B09
What are the names of the two electrodes of a diode?
A. Plus and minus
B. Source and drain
C. Anode and cathode
D. Gate and base
These are the anode and cathode (A & K), answer C. You may recognise these from electro-chemistry too.
T6B10
What are the three electrodes of a PNP or NPN transistor?
A. Emitter, base, and collector
B. Source, gate, and drain
C. Cathode, grid, and plate
D. Cathode, drift cavity, and collector
Emitter, base, and collector, answer A.
T6B11
What at are the three electrodes of a field effect transistor?
A. Emitter, base, and collector
B. Source, gate, and drain
C. Cathode, grid, and plate
D. Cathode, gate, and anode
Tricky, as each set relate to an amplifying or switching device. However, for the field effect transistor (FET) it is source, gate, and drain; answer B.
T6B12
What is the term that describes a transistor's ability to amplify a signal?
A. Gain
B. Forward resistance
C. Forward voltage drop
D. On resistance
This is its gain, answer A.
On to: Electrical Units & Metric Multipliers
You can find links to lots more on the Learning Material page.
Written by Julian Sortland, VK2YJS & AG6LE, January 2018.
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