Electronic Components Explained

Above are various batteries. Top left is your average 1.5V (AA), on the right of that is a less common 4.5V, then the largest battery is a 6V used in big torches, and on the far right is a 9V battery (PP3). On the bottom left are two 1.5V pill batteries like you'd find in a watch and two 3V batteries to the right, the one on the far right has small legs so it can be soldered to a circuit board.

An electric cell generates electricity from chemical energy as it discharges, and has limited use; this is a primary cell, common type of which include AA, AAA, etc. Those batteries that can be recharged, however, are secondary cells because they can be charged (electricity is converted to chemical energy) and discharged many times, but a finite number of times; common rechargeable batteries can be found in phones and portable computers.

Although the term cell and battery are used by most people interchangeably, they are not the same thing, as a battery consists of two or more cells connected in series, which increases the total voltage but keeps the capacity (ability to hold charge) the same. If different capacity cells are connected in series the total capacity is that of the lowest capacity cell. However, if same voltage cells are wired in parallel the overall voltage is no different from a single one but the total capacity is increased. You should never connect different type cells/batteries in parallel as they could explode.

Cells and batteries typically have their connections marked as negative (-) and positive (+) with the negative end often becoming the '0V' or ground point of a circuit. We can have a power supply, either derived from connected batteries or the mains, that has +V, 0V, and -V, which is known as a dual-rail supply.

An electrical circuit is the path through wires and components where electricity flows, from one end to another. Just as a runner makes his or her way from the start to the finish so do the electrons that make up the current, they travel from one end of the power supply to the other so as long as there is no break in the path.

You may wonder which way the electricity travels for a DC circuit (remember that the direction continually changes for AC), and there are two answers. It was originally thought that the electrons travelled from the positive (+) side of the supply and through the circuit to reach the supply's negative (-) connection. This is known as the conventional flow of electricity and even though it's wrong from an electron point of view, it is useful for understanding how a circuit works from a component level. But when detailing the workings of an individual component at low level, it is better to use the actual electron flow which is from the (-) terminal to the (+).

***Warning!***

The mains supply can kill. Never use equipment if the power cable is damaged, it must be replaced. DO NOT attempt to build, test or repair mains powered equipment if unsure of what you are doing. It really is better to be safe than sorry.

Since some form of power supply is essential for any electrical circuit to work, and in particular for mains powered devices, a lot of time, effort and money is put in getting it right. The power supply circuit will either be part of the main circuit, on a separate circuit board or will be sealed away inside a metal case that is earthed.

Above is an opened power supply from an Epson printer; note the three-pin mains lead socket at the front, the matrix of holes in the case that let the heat out, and the ribbon cable at the right which carries the different voltages to the main circuit board.

Any material which conducts electricity and thus has low resistance is a conductor, whereas the opposite is an insulator  which does not conduct electricity very well, though at very high voltages the insulator may break down and allow the current to flow, usually something you would want to avoid!

Think of an average wire; running through the middle is a length of thin metal (or thick wire if it's to carry high current) which conducts the current to its destination and around that conductor is the insulator (often plastic) that prevents shorting with other wires and contacts and protects anyone that may be handling the wire.

A word about wires, when they are grouped together they are often coloured coded but be cautious as the most obvious may be wrong. I stick to red for a positive voltage and black for the negative connection but I've seen people use the opposite so always check if you are repairing or testing a device you didn't make; don't assume.

Now let's look at some individual components and see how they work:

Switch

Where would we be without switches?! A switch, in its most simplest form, consists of two pieces of metal which the user pushes together to make a connection and thus allow current to flow. There are two main types of switches, those that latch (lock) into place, and those which don't, called momentary switches. On old computers the CAPS switch was of a locking type as was the power supply switch but modern computers have non-latching switches for the CAPS lock and power supply switch.

A selection of switches are shown below:

Whether the switch locks or not, when you press the switch it may either push the two connections together (said to be normally open or push to make) or the press may push the connections apart (known as normally closed or push to break). Some switches have both normally open and normally closed connections often with a common terminal (such as switch 3 in the image above); you may need to use one or the other, or both. Some switches can have ten connections or more, thus allowing different parts of a circuit to be turned on or off with just the one switch.

As well as switches that are pushed, there are also slide switches which can be pushed into a number of positions (e.g., switches 1 and 5). These switches are often used to make selections such as the voltage selection on a variable power supply. A similar type of switch that can be set to a number of different positions is the rotary switch (switch 10) which is turned to different positions, such as used on a washing machine or microwave. Some rotary switches can have the total number of turns limited by use of a washer with a tab that fits into a hole at the top of the switch.

Microswitches (switches 6, 13, 14 and 15) typically are quite small and require little force to operate and often of the non-locking type. Examples of where microswitches are used are in digital joysticks and joypads and as selection buttons on modern radios, CD players and the like.

Other switch variations include radio buttons (switch 8) which consist of a number of push buttons, only one of which can be pressed at a time (pressing one of the switches causes the other to become unpressed). These were often used in car radios to select a station but nowadays most people are probably more familiar with the virtual radio buttons used on computers.

DIP (Dual In-line Package) switches (switch 11) are made up of a number of individual switches which are most often used to make selections infrequently. For example, in a slot machine a DIP switch may be used to set various options, such as the maximum payout or whether to play sounds.

Another option switch is the binary or BCD (Binary-Coded Decimal) switch (switch 16) which allows the selection of a number indicated on the switch while representing the value in binary form on its contacts. This eliminates the need for an external encoder (to convert from decimal to binary) and reduces the number of connections that the switch needs. One use of this type of switch is to set the ID value of a system so that it can be identified on a network.

Switches are rated with the maximum voltage/current they can withstand and is usually written on large switches (a datasheet would have to be consulted for switches lacking such information). Either AC or DC (or both) ratings will be given but if there is only AC information it is usually reasonable to derate the AC value by half to derive the DC value.

Resistor

Probably one the simplest of components and one of the most common, a resistor restricts the flow of electricity, that is, it opposes the flow of current and causes a voltage drop across it. Many conductors have some resistance like a wire does, for example, but often its resistance can be ignored as it's so small. Resistors are made to especially limit the flow of current by a certain amount, within a given range called the tolerance. This resistance is measured in ohms (R), kilohms (1,000R or 1KR), and megaohms (1,000,000R or 1MR).

Above, are some electrolytic capacitors of different sizes, the small ones can store only 16V maximum while the larger ones can store 50V or more. But it isn't just the voltage that determines how large the capacitor is, its capacitance does also. That is, a capacitor that has large capacitance and can store a high voltage will be very large, such as those found in mains power supplies. However, even for the same voltage and capacitance the size will vary slightly depending on the manufacturer.

It is often electrolytic capacitors which fail in electronics either through old age, poor manufacturing process or badly designed airflow system causing unnecessary heat strain on components. When replacing capacitors you should always use a well known brand otherwise you will probably have to change the capacitors again shortly. Good quality electrolytic capacitors have a cross pattern on the top acting as a vent which stops the capacitor from exploding due to a fault in the circuit.

Some capacitors that are of small size can only handle a low voltage so you must make a point of checking that if you use such a capacitor that it will never be exposed to a voltage higher than that it is rated at, as indicated on its body. To be safe it is a good idea to use a capacitor that is rated as able to withstand at least double the voltage available in the circuit. Another factor that should be considered is the temperature range that the capacitor can withstand.

As seen in the photo above, capacitors come in different shapes, known as the type of package. The radial capacitors have both their leads originating from the bottom while the axial capacitors have a lead jutting out either side. The only real difference when soldering a circuit is that the axial capacitors take up more space than the radial type.

The charging and discharging of a capacitor can be delayed by using a resistor allowing time delays to be created. A simple timer can be created this way but there are far more accurate alternatives.

Similar to the variable resistor, a variable capacitor's capacitance is varied by using a dial and was once commonly used to change the station on radios and TV's. There are preset versions also, and one example of their use was to tune in the stations that a TV could receive, which could then be selected using the channel switches.

Light bulb

We are all familiar with light bulbs, such as the ones that keep our rooms lit, that serve as indicators in traffic lights, and so on. These traditional type of light bulbs work by passing a current through the filament wire which heats up to the effect that it gives off light. As well as the size and amount of light a light bulb gives off, light bulbs are rated by the maximum voltage and current they can withstand (usually written on the light bulb). Additionally, some light bulbs are designed to work on AC, others on DC.

Below you can see a photo showing a range of different types of light bulbs.

On the left is a mains powered light bulb that has wires connected, this is followed by a DC 'screw' type light bulb in a holder which has solder tags (if you try to solder directly to a light bulb it will most likely blow). Most of the other light bulbs are of the DC type, but the one on the end is an AC type designed to be powered by the mains.

Diode

Acting like a switch, a diode has two connections which are its anode and cathode. When the diode's anode is more positive than its cathode the component will have low resistance, allowing current to flow through it; it is said to be forward biased. However, when the diode's anode is more negative than it cathode the diode will block the current (except for a tiny amount known as leakage); in this mode it is reverse biased.

Because of its ability to control the flow of electricity, diodes are often used as rectifiers, that is, they convert AC to DC. This may be the case for power supplies that must deliver DC to the device it is powering and also in test equipment which accept an AC input but can only process it in DC form.

Another practical use of a diode that is possible because of its switching ability is in battery powered electronics where someone may insert the batteries the wrong way round. This could damage the components, but with a diode wired in series with the batteries it will not turn on unless they are connected with the correct polarity. There is a small price to pay for this feature; when current flows through the diode there will be a small voltage drop across it, something like 0.3V for a germanium (used rarely nowadays) diode or 0.6V for a silicon (the more popular material used to make diodes) diode.

Other types of diodes include Light Emitting Diodes, commonly referred to as LED's, which will only light when forward biased and, depending on its size, shape and the colour it produces, can work on as low as 20mA yet some can rival an ordinary lightbulb.

Lightbulbs have many disadvantages despite the fact that they're still so common; they can easily break and cause someone injury due to the glass, they need replacing often and are quite slow to turn on. But LED's on the other hand, last for ages, are made from plastic and come in shapes and colours that you just don't see with lightbulbs and the recent white LED's are bright enuough to put some lightbulbs to shame and they won't drain the batteries so quickly. One reason that lightbulbs are still used so much is that because of the small voltage drop across an LED (e.g., 2V), the component can easily be damaged by too high a voltage or too much current, thus a limiting resistor is used in series with the LED; whereas a lightbulb usually doesn't need such a thing.

There are hundreds of different types of LED's, but I will talk about the most common:

* The ordinary types of LED's just described come in many colours with red probably the most common, green, orange and yellow also available, and blue and white more recent inventions and operating at slightly higher voltages. As with coloured lightbulbs that are really just white but shine the colour of its glass this applies to LED's originally but now semi-see through (or milky) and totally transparent LED's that light up white or any other colour are ready to buy (you can see an example in the image below).

There are also LED displays with more segments so that more recognisable characters can be displayed and these displays typically have 14, 16 or even 22 segments. When you want to display even better looking characters or larger symbols you can use a dot matrix display which is made up of a number of round LED's. The LED's are commoned such that all the cathodes in a column are connected together and all the anodes in a row are commoned together, or the other way round. Below are 2 5x7 LED dot matrix displays which are useful for displaying characters:

The display on the right can be placed alongside other like displays horizontally and vertically to form a much larger display whereas the display on the left has space at the top and bottom which gives some separation between rows of characters, for example.

For more information about LED displays please go to LED Modules page.

You may also be interested in LED Faces Project page.

Optoelectronics, as is the name given to devices which produce or detect visible or invisible light, is truly wonderful but wait, there is more to talk about! Photodiodes detect infra-red light (such as transmitted by an infra-red LED), allowing remote operation of a device, such as a TV or CD player. A phototransistor is also capable of detecting infra-red light in which case light stimulates the phototransistor's base and because of its amplifying abilities a phototransistor is much more sensitive than a photodiode. A phototransistor may or may not have a base connection but if it does then the base lead can be used to bias the phototransistor.

If you couple (put together) an LED that gives off infra-red (or visible) light and a photodetector (photodiode or phototranistor) you create a slotted-opto switch; a non-transparent object that passes through the beam produced by the LED will be interrupted, causing the photodetector to switch off. This can then be detected and trigger the necessary response.

These slotted-opto switches are commonly used in the following:

* In printers as to detect whether there is any paper left.

* In arcade pusher machines to trigger a sound when a coin is inserted.

* In fruit machines as to sense when the wheels have reached their startup positions and to sync the wheels (as to check they're not out of line).

* In traditional computer mice to detect movement.

* To detect if a moving part has reached a certain place (such as the print head in a printer).

Although more expensive than mechanical switches, slotted-opto switches last longer, and can be used without direct contact since it's light that is interacted with. Slotted-opto switches, however, aren't self latching by nature and not as simple to use as the mechanical equivalent. Slotted-opto switches are sometimes used like a mechanical switch by having a hinged plastic part that can be pushed, blocking the infra-red beam.

Slotted-opto switches have either four connections, or three if two of the connections are commoned. With those that use a phototransistor It may be the cathode and emitter connected together (most likely) or sometimes the anode and the collector. The anode, cathode, collector and emitter may be marked on the body of the slotted-opto switch (as A,K,C and E respectively) or you'll have to try out the different combinations as colour coding where wiring is concerned is hardly trustworthy. If the connections are unknown first start by working out the LED connections; an infra-red LED when turned on will show up as pink or purple when viewed using a digital camera. As for the photodetector, you can use the diode tester on a multimeter for checking a photodiode. If a phototransistor has been used and a base connection has been provided you can also use a diode tester as, assuming an npn transistor, the base is equivalent of a diode's anode and, the collector and emitter are equivalent of a diode's cathode. A transistor tester can also be used to test a phototransistor if it has a base connection.

There are also reflective opto-switches which are made very similar to slotted-opto switches but rely on a reflective object bouncing the infra-red beam towards the phototransistor. And finally, an opto-isolator has both a photodiode and phototransistor housed in a chip-like package, isolating two separate voltages yet allowing one voltage to affect the other, much like a relay does in that a small voltage triggers the relay, causing it to turn on a much higher voltage.

I hope it's becoming clear that the solid state versions of the mechanical equivalents are so much better, partly due to the lack of moving parts (hence solid state) that wear out with mechanical switches and relays. However, as great a keyboard would be made up of solid state switches, it would be too expensive and require more power than an ordinary keyboard, so there are still many valid reasons to use mechanical switches.

As already mentioned with regards to LED's, applying too high voltage or current to a diode in forward or reverse biased mode can damage it. LED's, just as with ordinary diodes, can be damaged if exposed to too much heat, so when soldering also use a heatsink with these and other semiconductors or failing that, be lightning quick!

Transistor

Probably one of the greatest inventions ever, the transistor has made possible the miniaturisation of electronic devices like radios, cassette players and so on. A transistor is a three terminal component which acts as a switch in that it controls the flow of electricity much like a diode, and also serves as an amplifier (a small current controls a much larger current). Transistors are designed to be either best at switching current or amplifying though there are so called general purpose transistors that are average at both jobs.

The decision making logic gates that have made possible the computers of today are made up of many transistors that switch on and off rapidly as to make calculations and to store data. This digital control of data is how binary values are manipulated as it is easy to handle just ones and zeroes at the lowest level.

When a transistor is used as an amplifier, it controls the output so that it is a larger but faithful representation of its smaller input (as much as is possible practically). Thus a transistor cannot deliver current that doesn't exist, it simply controls the available current according to the input signal. Usually the term amplifier is used to mean in general equipment that produces a louder replica of the original sound coming from something like a microphone, whereas the 'amplifier' will actually contain many transistors working together in addition to other, different components.

How well a transistor increases the power of an input signal that it delivers at its output is known as its gain, the ratio of output to input.

Transistors come in a number of different shapes and sizes with the larger transistors able to tolerate more heat than the smaller ones and can be mounted to a heatsink. The following photo shows a selection of transistors with their package types labelled using the TO (Transistor Outline) standard. Note that components other than transistors (e.g. voltage regulator microchips) can also use TO packages.

From the left (case style/part name/description):

TO-92: 2N3906: PNP silicon general purpose amplifier

TO-1: AC128:  PNP germanium small signal amplifier

TO-39: BFY51: NPN silicon general purpose

TO-126: BD139: NPN silicon general purpose

TO-220: D1159: NPN silicon high current switching

TO-3: 2SC1617: NPN silicon B/W TV horizontal output 

Microchip

Better termed the Integrated Circuit or IC, it is an electronic component that contains hundreds, thousands or more miniature components connected on a microscopic scale, permitting complex circuits on a tiny scale. Thanks to these chips, handheld devices more advanced than the computers that once filled an entire room are so common we perhaps couldn't imagine a life without them. Although not every component can be scaled down as to fit inside an IC, and some components have to be emulated by others, a great number of transistors can be packed onto a silicon chip, serving primarily as switching or amplifying devices.

Take a look at the photo above, which shows a number of IC's, which shows just a few of the many case styles (packages) of IC's. The top left three chips are known as Dual in-line (DIL) or Dual in-line package (DIP) - the terms are generally use to mean the same thing - because they have connections parallel to each other on two sides. Of those IC's mentioned, the very left one has 8 connections (pins), the next to the right has 16 pins, and the next along 28 pins. These types of chips typically have a pin pitch - the distance between pins - of 2.54mm (0.1") and will happily fit into breadboard/prototype board.

When used on circuit boards, typically, DIL chips are part of a process known as through-hole as their pins are pushed through holes in the board and soldered on the other side. Alternatively, a DIL IC may be placed in a chip holder which allows for easy removal should it need to be replaced, upgraded, or if it needs to be re-programmed if it is a programmable chip. It was also common practice by some manufacturers (e.g. Commodore) to solder a socket when the particular chip wasn't available, keeping the production line moving and allowing the insertion of the chip(s) when the stock was received - such practice helps with the maintenance of such electronics in modern times. Additionally, hobbyists often use chip holders in their projects rather than solder chips directly to a board to avoid damaging the chip through excessive heat.

Top right we have a 'metal can' TO-99 IC which has 8 connections protruding from two sides. This package type was only used in old electronics and only for chips that had a low number of pins. If you have read the Transistors section then you will have seen that some transistors use a similar package style.

At middle left there is a 64 pin DIL IC which is probably the biggest DIL IC that has been made and is large because of the pin spacing and having to route the many connections from the small slice of silicon to the many pins. As we shall see there are smaller package types and indeed the chip featured had smaller versions produced.

The chip at middle right resembles a transistor and in fact uses a variation of the TO-220 transistor case style called TO-220-7B. The '7' in the name usually refers to the number of pins but this IC has only 5 pins with spacing of two intentionally absent pins (which totals 7).

There is another DIL chip bottom left and this one has 40 pins. It is worth mentioning that with DIL IC's, two chips with the same number of connections may be two different sizes.

Lastly, the chips at bottom middle and bottom right have the Plastic Leaded Chip Carrier (PLCC) package type. The bottom middle IC has 32 pins and is known as PLCC32 whereas the bottom right chip has 44 pins and has the package type PLCC44. PLCC IC's are an example of a package type that uses Surface-Mount Technology (SMT), such a component itself being referred to as a Surface Mount Device (SMD). The chip pins are soldered to the surface of the circuit board and because of the small chip package size and being surface mounted circuit boards can be much more packed with components and on both sides too. PLCC chips can be placed into an appropriate chip holder which itself may use SMT or through-hole connections.

Common markings to find on an IC are the manufacturer's name or logo, the part number and date. Often the first two letters of the part number represent the company name (e.g. NE555, LM555, ...) but some manufacturers will use different numerical values for an equivalent IC (e.g. both LM1455 and NE555 refer to 555 chips). You may find a letter at the end of the part number which typically signifies the package type which is more useful when ordering a chip rather than when you have the chip in hand. Sometimes there will be a number of letters in the middle of the part number that gives some extra information about the chip's capabilities.

Because of the small size of SMD chips often the part number is a shortened version, which can create difficulty if you are trying to work with chips second hand that you have no information about, you may get lucky with a Google search and find the datasheet.

Most often the date has four digits and is in the form YYWW (e.g. 7405 is the 5th week of 1974) which can get a little confusing when the date is very similar to a part number. Using four digits isn't Y2K friendly but this isn't a big problem at the moment as a modern date code such as 1523 (23rd week of 2015) clearly doesn't refer to 1915 as microchips weren't around then.

Universally, a dot on the chip's top surface indicates where the first pin is; numbering increases by one for every pin in an anti-clockwise order. Every pin of a chip has a different function (although sometimes there are unused connections) so it is vital that IC's are connected correctly in a circuit. A pinout (or pin-out), as found in a chip's datasheet, lists what every pin does and its characteristics, such as the acceptable voltage range or the timing constraints. Even for the same component, different package types may have different pinouts.

There is one more major type of IC package to mention which is known as Chip On Board (COB), which have the form of a (usually) black blob that sits on the surface on the circuit board and are often custom chips, allowing for a reduced cost in production and small footprint. Although not always the case, COB chips can be found in counterfeit products and because they have no markings on them they can be difficult to identify.

It's easy to split microchips into two different types in terms of function, they are analogue and digital, although there are hybrids too. Analogue IC's specialize in amplifying and voltage regulation while digital chips cater for control circuitry and memory solutions. A typical computer will contain lots of microchips working together to direct and manipulate data; the Central Processing Unit (CPU) is one of the most famous and important, though it would not be able to do much without one or more memory and control chips as well.

Two of the most famous family of logic IC's are the 7400 and 4000 series which you can read about at:

https://sites.google.com/site/jamesskingdom/Home/electronics-by-james-s/digital-electronics-by-james-s#TOC-Logic-IC-s

Some of these logic chips are used as 'glue logic' that is, a means to provide an interface between different components (often IC's). For example, if a chip outputted a high signal when a particular condition occurred but you needed to feed that output to another chip which expects a low signal when the condition occurs then you could use an inverter gate to invert the signal.

You can read more about logic gates at:

https://sites.google.com/site/jamesskingdom/Home/electronics-by-james-s/digital-electronics-by-james-s#TOC-Logic-Gates

Another common use of IC's are as voltage regulators which make sure that there is a stable voltage in a circuit, which is very important for components that need a fixed voltage that stays the same regardless of how much current is being drawn, within practical limits. An example would be digital circuits, which are sensitive to fluctuations in voltage changes, and in an example digital circuit you may have multiple voltage regulators outputting different voltages.

Common fixed voltage regulators (that is, the output voltage remains at a set voltage depending on the IC type) are the 78xx series for positive voltages and the 79xx series for negative voltages. For example, the 7805 will always give a +5V output and a 7912 will output -12V, however, the output voltage won't be dead on, it may be slightly out (e.g. +5.2V). Each of these voltage regulators have three connections (input, ground and output) and come in different case packages suitable for the amount of current they can deliver. 78xx and 79xx voltage regulators with no letter in the middle (e.g. 7905) are rated for 1A with a suitable heat sink; those that have an 'L' in the middle (e.g. 78L12) are limited to 100mA; an 'M' in the middle (e.g. 78M05) denotes max current of 500mA; an 'S' (e.g. 79S05) is capable of 2A. Note that each version of these 78xx and 79xx voltage regulators have a different pinout.

Another form of voltage regulator is the variable voltage regulator but this type of voltage regulator isn't just useful for altering the output voltage as you might expect as they are also useful for providing a fixed, precise voltage. Let's say you needed 3.2V regulated but there was no fixed voltage regulator that could output 3.2V then you could use a variable voltage regulator but set it to always output 3.2V.

An example of a variable voltage regulator is the LM317 which has three connections: input, adjust and output. By using a combination of two resistors you can set the output voltage as needed. Like with the 78xx and 79xx series, the LM317 comes in different forms based on its current carrying capabilities.

Vacuum Tube

Known also as a valve, the vacuum Tube is a type of electronic component which in essence is much like a traditional light bulb (incandescent) but can be made to control electricity including amplifying. The vacuum tube date to the early 1900's and was first used in radio circuits before making its way into more sophisticated electronics such as the early computers.Typical valves contain two or more electrodes (grid and anode) and a heater (the filament); a small current passing through the grid controls the (larger) current flowing from the heater to the anode, making it an amplifier.

Valve names are derived from the number of electrodes the valve has. So, diode means two electrodes, a triode has three electrodes, a tetrode has four electrodes, a pentode has five electrodes, and so on. You can even get vacuum tubes that are in effect two valves in the one enclosure which saves space. It's interesting that the term diode is still used for the solid state version of the valve diode.

Although valves have been greatly replaced by solid state equivalents they are still in use in applications using high power and in audio equipment because of the unique sound they give. Valves are still used in microwave ovens (the magnetron) and let's not forget that the CRT (Cathode Ray Tube) was the main form of display for TV's and monitors until LCD's replaced them but even so some people prefer CRT based screens because of the their quick response. Many people like the glow of a Vacuum Fluorescent Display (VFD) as found in a VCR, for example, and the Nixie tube (cold cathode display) is still loved by a great number of hobbyists because of the display's appealing look.

While valves in their early days were a huge advancement in electronics they have a number of disadvantages that have resulted in the decline of their use. For one thing, valves are much larger than more modern components which you can see below:

Just try fitting one tube inside a modern smartphone!

On the left in the photo above is a transistor, a component very commonly used in modern circuits, and on the right is a vacuum tube, which this particular one is used in power supply circuits. While it is possible to get smaller valves, a transistor is much smaller, more reliable, and millions of transistors can be placed on a tiny slice of silicon. This was one of the reason that valve computers (back in the 1940's) filled an entire room yet the power of one of those computers is only a fraction of what is possible with microchips available today.

Valves have a high failure rate as, like an incandescent light bulb, it is the inrush current that flows when a device is turned on that can kill a valve so if the equipment is left on the valves should last longer. To make replacing valves easier they are usually socketed which gives a unique look when they are mounted on top of equipment. Back in the day valve equipment would use point-to-point wiring and you will find that some valve sockets have an extra, middle pin to use as you please (e.g., to use as a common ground point).

Another disadvantage of the vacuum tube is that it is made of glass and so has to be handled with more care than a modern component, such as the transistor. Valves generally are more difficult to use than other components because of the multiple voltages involved which are typically a low voltage supply for the heater (~6V) and a very high (100V or more) supply for the anode voltage. One way to get the high voltage for valve equipment is to simply rectify the mains which in consequence means the circuit can be powered from AC or DC. A much safer method is to use a low voltage AC input for the heater (the heater can use AC or DC) then stepped up and rectified for the anode voltage.

Valves are also inefficient compared to modern components such as transistors as they waste power in the heater, which needs time to warm up. Because of the heater some valves glow when they are on and this can be an indicator if a valve is working, however, some tubes don't glow much at all.

You may like to check out the Valve Projects page.

All content of this and related pages is copyright (c) James S. 2007-2024