Identifying components: Part Two

In this article, we will explore the identification of larger components than the ones used in effect builds. This article partly repeats the first one, as the principles of identification remain largely the same.

Electronics components are divided into two groups: passive and active. The naming is based on the part's function; for the purpose of this article, we will simply state the facts as they are. Passive components include resistors, capacitors, inductors, and transformers. Active components include tubes, diodes, transistors, and other semiconductors. Additionally, electromechanical parts such as switches and connectors are used in building. Tube amplifiers use a socket for each tube.

This article will focus on components used in tube amplifiers. We will cover what the components look like, how to interpret and read their markings, and where they are installed. The technical characteristics of the components are outside the scope of this article.

Resistors, Trimmers, and Potentiometers

Resistor symbols in circuit diagrams. The box represents the European practice, while the sawtooth represents the American practice. P1 and P2 represent the symbols for trimmers and potentiometers.
Various resistors from left to right: 1k 0.25W carbon film resistor, 1k 0.6W metal film resistor, 1M 0.5W carbon composition resistor, 2W metal film resistor, 10k 1W carbon film resistor, 100ohm 5W wire wound resistor, 1k 10W wire wound resistor.

Resistors used in tube amplifiers vary depending on the circuit and sometimes style preferences. Lower-power resistors are almost always marked with color bands. Depending on the type of resistor, the value is indicated with either three or four bands. A fourth or fifth band slightly separate from the others indicates the tolerance of the resistor, usually in percentage. Tolerance and the number of bands are somewhat linked; higher tolerance parts are not marked as precisely.

Power resistors are marked numerically. Some manufacturers may use the letter R instead of the Ω symbol, and in some cases, the unit symbol may be used as a decimal point, e.g., 0R22 = 0.22 ohms.

The first two (or three) bands indicate the first digits of the resistor's value, and the last band indicates the number of zeros. For example, red - violet - brown turns into the numbers 2 - 7 - 1 = 27 and one zero, which means 270 ohms. In metal film resistors, the numbers have three decimal places, so the corresponding metal film resistor is marked red - violet - black - black = 2 - 7 - 0 and zero zeros, meaning 270 ohms.

The multipliers for resistor values are:

• kilo (k) = ×1000

• mega (M) = ×1,000,000

Because reading and remembering color codes can sometimes be difficult, you can use online color code converters (search for "resistor color code") or use a multimeter. Most multimeters require you to select the measurement range, so choose according to the size of the resistor you are looking for in the component bin. However, we recommend learning the basics of color codes. For example, it's easier to find all the parts starting with a 2 if you first set aside all the parts marked with a red stripe.

Resistor markings on a PCB. At the top, the soldering points for a vertical resistor (one lead bent to align with the casing direction). Marking styles vary: either part numbers like R1, R2, or a specific value, such as 10kΩ.

If the kit uses a PCB, resistors will always have their symbol or a pattern corresponding to the part's shape printed on the board. Additionally, the part's designation or value will be printed on the board. The symbol for resistors is R (resistor). Resistors can be installed on the board either way. However, it's recommended to install them in the same orientation to make future repairs and error detection easier.

Adjustable resistors: Left to right: trimmer, 1kΩ 16mm linear potentiometer, 1MΩ 24mm logarithmic potentiometer, 16mm potentiometer for PCB mounting.

A special application of resistors is the adjustable resistor. These include trimmers, which are adjusted once, and potentiometers, which are designed for continuous adjustment, such as a volume control. An adjustable resistor has three pins. The outer pins are the ends of the resistive track, and between them is a resistive track that corresponds to the nominal value. The center pin is connected to a contact that moves along the track, changing the resistance depending on the position of the potentiometer.

Capacitors

Capacitor symbols. C1: Ceramic or plastic capacitor with no polarity. C2: Electrolytic capacitor (white box indicates the positive terminal). C3: Bipolar electrolytic.
Capacitors: From left to right: 10pF ceramic capacitor, 22pF Silver Mica, 47nF plastic film capacitor, 15nF PIO (Paper In Oil) capacitor, 220nF and 47nF plastic film capacitors, 100uF and 22uF axial / horizontally mounted electrolytic capacitors, and 32uF + 32uF can-type mounted capacitor.

In capacitors, the capacitance unit is large, so values are always given with multipliers. These are pico (p), nano (n), and micro (µ / u). Since micro is typically the largest practical unit, the multipliers go as follows: 1uF = 1000nF = 1000000pF.

In amplifiers, three types of capacitors are most commonly used. Low capacitance capacitors are ceramic (10pF - 1nF) or silver mica types (1nF - 1uF) or plastic film capacitors (1nF - 1uF). Higher capacitances use electrolytic capacitors (1uF and above).

Capacitor value marking methods are varied. Ceramic capacitors use numbers to indicate their value. The first two numbers indicate the first two digits of the capacitance. The third number shows how many zeros follow. For example, 101 = 100pF, 102 = 1nF. Values under 100 use no multiplier, e.g., 10 = 10pF.

Plastic film capacitors indicate the value either in nano or micro units. The unit is not always marked; 100nF could be marked as 0.1, .1, or u1. The unit symbol "u" can also be used as a comma, e.g., 2u2 = 2.2uF. Generally, the smaller the part, the shorter the marking.

Electrolytic capacitors typically have the capacitance value printed in uF on the part itself.

All capacitors will also have a maximum voltage rating. There may be multiple capacitors with the same capacitance but different voltage ratings (e.g., 25V and 450V). Always follow the specified voltage rating. The voltage rating must always exceed the required voltage.

Capacitor markings on the PCB. On the left are solder points for ceramic and plastic film capacitors, in the middle are vertical electrolytic capacitors and on the right are horizontally mounted electrolytic capacitors. The terminals are marked with a + or - stripe. Horizontally mounted electrolytics have a groove marking the positive terminal side.

On the PCB and in the parts list, the symbol for capacitors is C. Capacitors are printed according to their shape, and electrolytics are marked with polarity. Ceramic and plastic capacitors can be installed either way. Electrolytic capacitors are marked with either a + or - stripe. Horizontally mounted capacitors have a groove marking the positive terminal side.

Diodes and LEDs

Diode symbol. D1: standard diode, center: LED. D2: Zener diode.
Diodes. From left: 1N4148 silicon diode, BAT42 Schottky diode, 1N34 Germanium diode, 1N4007 silicon diode, UF5408 Ultra Fast silicon diode. All cathodes (stripe on the casing) are up. On the right: two LEDs, 3mm and 5mm. Cathodes (-) are on the left.

Diodes allow current to flow in only one direction, so correct polarity must be followed during installation. Diodes have the negative terminal (cathode) marked with a ring. One type of diode is the LED, which, in addition to producing light, functions like a regular diode. The polarity of an LED can be identified either by the length of the leads (short lead marks the cathode), the bevel of the casing (bevel cathode), or the internal element shapes (larger triangle cathode).

The part marking is straightforward – the type marking of the part is printed on the side of the component. In some cases, the prefix may be omitted (e.g., 1N4007 becomes 4007).

Marking methods for diodes on a PCB. Left: vertical mounting, with anode and cathode markings.

The diode marking on the PCB is similar to resistors, with the exception of the polarity stripe, which is also printed on the part. The part marking for diodes is D, for LEDs it is LED. For vertical mounting, the polarity is marked A for anode and K for cathode. For LEDs, the print typically marks the beveled side of the casing.

Zener diodes are variations of standard diodes. The amount of forward voltage varies, so these diodes can be used to achieve a specific voltage.

Transistors, FETs, MOSFETs

Transistor circuit symbols. T1 and T2 are two different ways of drawing a transistor. T3 is a JFET, and T4 is the symbol for a MOSFET transistor.


Transistors have a specific function for each pin, so installing the part correctly is important. Depending on the type, the pinout can vary, but in kit builds, the part’s pinout corresponds to the PCB print.

Transistors. From left: 2N3906, center: two power transistors, BD139 and BD243. On the right: STW11NK100Z power MOSFET.

Markings on transistors are clear, with the type designation printed on the side of the casing.

Various transistor marking styles on a PCB. On the lower right, the marking for a power transistor. The white line indicates the side of the part where a possible heatsink will be attached. This is usually the bare metal side.

The transistor part marking on the PCB is T (or in some cases Q). The installation of transistors on the PCB follows the direction of the casing shape and the PCB print. In some cases, the same PCB may be used for different types of parts (e.g., a silicon transistor replaced by a germanium transistor), so the builder must determine the correct installation direction separately. Note: Some ICs, such as 78Lnn series regulators, are packaged the same as transistors, and their installation on the PCB follows the same rules.

Tubes and Tube Sockets

There are different types of tubes depending on their purpose and electrical characteristics. Most amplifier tubes are either nine-pin noval-based tubes (for preamps) or octal-based tubes (for power stages) and rectifiers. This is a rough generalization, as in reality, preamp tubes can be found on octal bases, and rectifiers and power tubes can be found on noval bases. In octal-based tubes, some of the pins are omitted if they are not electrically needed.

Tubes and sockets. On the left, a noval-base preamp tube and its socket. On the right, an octal-base power tube and its matching socket.

In addition to these two common amplifier types, there are tubes and sockets ranging from four contacts to over ten.

Tubes and sockets usually have markings for the pin numbering. Octal-base tubes have a guide pin in the center of the tube/socket, which has a groove. In noval-base tubes, the tenth pin position is empty. Always install and wire the socket according to these guides.

Transformers and Chokes

Different transformers. On the left, two power transformers, one with wires and the other with solder terminals. On the right, a ring-core transformer. Always check the color code of the wires in the documentation provided with the transformer.

All tube amplifiers use transformers and almost all use chokes. Transformers are used to convert the AC voltage to a level suitable for tubes, as well as in impedance matching from the power stage to the speaker. Chokes are used to improve the power supply filtering.

Transformers are either built into a square metal case or a round laminated metal core (toroidal). Chokes are always housed in metal cases.

The wiring method varies by manufacturer. Some transformers have numbered solder tabs, while others have short wires (30-50 cm). In this case, identification is done according to the insulation color of the wires.

Other Components Used in Circuits

In addition to the parts mentioned above, circuits may use coils, opto-isolators, rectifier bridges, etc. The part listings for these components often match the English name of the part and indicate the correct orientation according to the silk screen print compared to the housing markings or notches.

Mechanical Parts - Switches, Jacks

Switches. On the left, an SPDT toggle switch, DPDT toggle switch, 3PDT foot switch, and a DPST toggle switch for AC power.

There are different types of switches. A basic switch could be called a standard on-off switch (abbreviated SPST). This has exactly one function: power is either on or off. Since there are two positions, it is natural to use a toggle switch, on-on (abbreviated SPDT). In this type of switch, there are three terminals. The middle terminal connects the signal to one of the two outer terminals.

These toggle switches can be installed mechanically in parallel with multiple positions. Switches typically have between two and four positions (DPDT, 3PDT, 4PDT). Foot switches often have three positions. A switch with nine terminals total must be installed carefully to avoid wiring errors, such as turning the switch 90 degrees.

Terminology: The abbreviations tell both the number of poles and the number of throws. S=single, D=double. SPDT=Single Pole, Double Throw, one switch, two positions. 3PDT=three switches, two positions.

6.3mm jacks. On the left, a plastic-cased mono jack. Pictured from the back: mono jack, mono jack with switch, and stereo jack.

There are also different types of jacks. In effects, mono or stereo jacks are typically used. A mono jack has two terminals, one for the signal (tip) connected to the plug. A stereo jack has three terminals.

In open-type jacks, the ground or housing terminal can be identified as it is directly connected to the center shell used to mount the jack to the chassis.