Differences between Pro Electron and earlier valve-naming conventions

• Unlike the tube naming convention, if there are two transistors in a single envelope, the type letter was never repeated - so a dual NPN RF transistor might get a type "BFM505" rather than something like "BFF505" for instance.
• Although some of the most popular devices conform to a pattern of serial numbers that identified package type and polarity, many do not.
• The letters assigned for the second character of transistor and diode type numbers differ in several ways, e.g.
  • "B" tends to be used for dual varicap diodes
  • "L" in the context of transistors designates RF power (transmitting) transistors; for valves it meant a high-power pentode tube (the usual choice for power RF)
  • "Z" is used for semiconductor Zener diodes instead of (full-wave) rectifier valves (tubes).

Frequently used first letters in European active devices

• • A Germanium (or any semiconductor with junctions in a material with a band gap of 0.6 to 1.0eV)
  • B Silicon (or band gap of 1.0 to 1.3eV)
  • C III-V semiconductors with a band gap of 1.3eV or more, like gallium arsenide in LEDs
  • D may be...
    • Semiconductors with a band gap less than 0.6eV, such as indium antimonide in infrared detectors (rarely used), or
    • (Mullard–Philips) 1.4V (or less) filament tubes
  • E (Mullard–Philips) tubes with a 6.3V heater
  • F Digital integrated circuits
  • P (Mullard–Philips) tubes for a 300mA series heater supply
  • R Devices without junctions, e.g. cadmium sulfide in a photoresistor
  • S Solitary digital integrated circuits
  • T Linear integrated circuits
  • U may be...
    • (Mullard–Philips) tubes for a 100mA series heater supply, or
    • Mixed digital/analogue integrated circuits

The first letter gives the semiconductor type

(see above)

The second letter denotes the intended use

The serial number

Following these two letters is a 3- or 4-digit serial number (or another letter then digits), assigned by Pro Electron. It is not always merely a sequence number; there is sometimes information conveyed in the number:

• In early devices only, the serial number often indicated the case/package type (e.g. AF114-7 for TO-5 case, while AF124-7 were TO-72 versions of the same transistors); modern surface-mount devices often begin with "8",
• early silicon transistors followed the convention of using a middle digit of 0-5 for NPN and 6-9 for PNP.
• the last digit often indicated a particular specification or application grouping, e.g. the AF117 and AF127 were similar IF amplifier devices in different cases; the BC109, BC149, BC169 and BC549 are similar low-noise transistors).
• some modern devices use letters, such as "B" to indicate HBT bipolar transistors.^[1]

Suffixes and version specifiers

Suffixes may be used, letters or perhaps blocks of digits delimited by "/" or "-" from the serial number, often without fixed meanings but some of the more common conventions are:

• for small-signal transistors "A" to "C" often means low to high h_FE, such as in: BC549C^[2]),
• numeric suffixes may be used as an alternative way to show h_FE (e.g. BC327-25), or voltage rating (e.g. BUK854-800A^[3]).
• for voltage reference diodes letters show the tolerance ("A","B","C","D","E" indicate 1%/2%/5%/10*/20%) and may be followed by the V_z value, e.g. 6V8 for 6.8 Volts or 18V for 18 volts.
• "R" can mean "reverse polarity".

Examples of suffixes and manufacturers' extensions to the basic sequence number include:

Note: A BC546 might only be marked "C546" by some manufacturers, thus possibly creating confusion with JIS abbreviated markings, because a transistor marked "C546" might also be a 2SC546.

Short summary of the most common semiconductor diode and transistor designations:

      BC549C
     / |--- \___ variant (A,B,C for transistors implies low, medium or high gain)
    /  |   \____ serial number (at least 3 digits or letter and 2 digits)
   /  device type:
A=Ge     A=Signal diode
B=Si     C=LF low-power transistor
         D=LF Power transistor
         F=RF transistor (or FET) 
         P=Photosensitive transistor etc.
         T=Triac or thyristor
         Y=Rectifier diode
         Z=Zener diode

Usage in the Eastern Bloc

Poland, Hungary, Romania, and Cuba mostly used Pro Electron designations for discrete semiconductors just like Western Europe. Starting in 1971, in Poland the letter "P" was inserted, e.g. BUY54 became BUYP54.^[4] Kombinat Mikroelektronik Erfurt (KME) in East Germany and Tesla (Czechoslovak company) used designations derived from the Pro Electron scheme. In particular, the first letter specifying the material differed while the second letter followed the table above (with the few exceptions for KME noted below).^[5]

Examples: GD241C - Germanium power transistor from KME; MB111 - optoisolator from KME; KD503 - Silicon power transistor from Tesla; LQ100 - LED from Tesla.

Digital logic families

The combination of first letter and second letter is assigned to a specific manufacturer.^[1]

   FCH171
  //  \ \__ serial number (including temperature range)
 //    \___ H=gate ("Combinatorial circuit"), J=flip-flop, K=monostable, L=level shifter, Q=RAM, R=ROM, Y=miscellaneous etc.
FC=DTL by Philips[9] / Mullard[8]
FD=dynamic PMOS by Philips[9] / Mullard[8]
FE=PMOS by Philips[9] / Mullard[8]
FH=TTL by Philips[9] (SUHL II series)
FJ=TTL by Philips[9] / Mullard[8] (7400 series)
FK=E2CL by Philips[9]
FL=TTL by Siemens (7400 series)[10]
FN=ECL by Telefunken[11]
FP=HTL by Telefunken[11][12]
FQ=DTL by SGS-ATES[13][14]
FS=SECL by Telefunken[11]
FY=ECL by Siemens[10]
FZ=HTL by Siemens[10]
GD=PMOS by Siemens (MEM1000 series)[15]
GH=ECL by Philips[16]
GJ=TTL by Mullard (74H00 series)[8]
GR=interface devices by Mullard (7500 series)[8]
GT=TTL by Mullard (74S00 series)[8]

Unfortunately the serial number does not specify the same type of gate in each family, e.g. while an FJH131 is a quadruple 2-input NAND gate (like the 7400), an FCH131 is a dual 4-input NAND gate,^[8] and an FLH131 is an 8-input NAND gate (equivalent to 7430).^[10] To lessen the confusion at least for the 7400 series, at some point manufacturers included the well-known 7400 series designation both in their literature and on the integrated circuits themselves.