European Pro-Electron system

Transistors, diodes and similar devices were originally treated as zero-filament voltage thermionic devices and given numbers prefixed OA and OC. Today they are defined by two letters followed by a serial number (three figures or one letter and two figures). The serial number is manufacturer-dependent. The initial two letters define the device function as follows:

FIRST LETTER: Indicates the semiconductor material used:

A - Germanium
B - Silicon
C - Compound materials such as gallium arsenide
D - Compound materials such as indium antimonide
R - Compound materials such as cadmium sulphide

SECOND LETTER: Indicates the general device function:

A - Detection, high-speed or mixer diode
B - Variable capacitance diode
C - Transistor for AF (not power) applications
D - Transistor for AF power applications
E - Tunnel diode
F - Transistor for RF (not power) applications
G - Miscellaneous devices
L - Transistor for RF power applications
N - Photo-coupler
P - Radiation sensitive device (such as photo diode etc.)
Q - Radiation generating device (such as light emitting diode)
R - Controlling or switching device (not power) such as thyristor
S - Transistor for switching (not power) applications
T - Controlling or switching power device
U - Transistor for power switching
X - Multiple diode (such as varactor)
Y - Rectifier, booster or efficiency diode
Z - Voltage reference, voltage regulator or transient suppressor diode

NORTH AMERICAN (JEDEC) SYSTEM

The Joint Electronic Device Engineering Council devised a system using a numeral, the letter N and a registration number of two, three or four digits. The first numeral indicates the number of diode junctions; 1 = diode, 2 = transistor, 3= FET. The prefix JAN (joint army/navy) indicates a military specification variant of the transistor.

JAPANESE SYSTEM

Japanese transistors are numbered in series commending 2S and one more letter, then two, three or four figures. The series are 2SA, 2SB, 2SC, 2SD (including both germanium and silicon devices). A= p-n-p, radio frequency applications; B = p-n-p, audio frequency, C = n-p-n, RF and D = p-n-p, AF The 2SJ and 2SK series are all FETs.

Note that the first two characters (e.g. 2S) are normally omitted on device markings, so a 2SC438 transistor will normally be marked C438.

SOVIET SYSTEM

A code of one letter and three digits is used; the letter D denotes a diode and P denotes a transistor.

For Germanium diodes, 1-100 are point-contact types, 301-400 are junction types, 401-600 are mixers, 601-800 are video types and 1001 and above are rectifier stacks. For silicon diodes, 101-200 are point-contact types, 201-300 are junction types and 801-900 are zener diodes.

Transistors are numbered P1-100 germanium LP/LF, P101-200 silicon LP/LF, P201-300 germanium HP/LF, P301-400 silicon HP/LF, P401-500 germanium LP/HF, P501-600 silicon LP/HF, P601-700 germanium HP/HF and P701-800 silicon HP/HF. LP is low power, below 0.25W, HP is high power greater than 0.25W. LF is low frequency up to 5MHz, HF is high frequency above 5MHz.

BRITISH GOVERNMENT TRANSISTORS

Transistors used by the armed services and the Post Office were also numbered in the CV (common valve) series. Some Post Office types were numbered PO1, PO2, etc.

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