Mullard–Philips tube designation
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In Europe, the principal method of numbering vacuum tubes ("thermionic valves") was the nomenclature used by Mullard in the UK, and in Europe by the parent company Philips and its subsidiaries in Germany (Valvo) and France (Dario), from 1934. This system allocated meaningful codes to tubes based on their function. This European common code system became the starting point for the Pro Electron naming scheme for active devices (including tubes and transistors).
The system allowed for cross-referencing with the American RETMA tube designation, the Marconi-Osram tube designation, and with military numbering systems such as common valve (CV) numbering in the United Kingdom and the Joint Army–Navy (JAN) tube designation in the US. European tube manufacturers agreed on the system, but in the UK MOV (Marconi-Osram Valve), Brimar (STC) and Mazda/Ediswan maintained their own systems. Most MOV tubes were cross-licensed copies of RCA types, with a British designation. For example an MOV X63 valve was the same as an RCA 6A8 tube. Brimar, which stood for "British Manufactured American Radio" (valves), used all American designations. Brimar/STC was a UK subsidiary of the American giant ITT (International Telephone and Telegraph).
Special quality tubes for military use were sometimes identified by placing the numerical part of the designation between the heater rating and the tube type. For example an EF80 manufactured as a special quality tube would be designated 'E80F'. The system was not universal as other special quality designation systems existed. For example, an EF91, in its special quality version was designated 'M8084' (the 'M' meant Military) as in this case the standard EF91 was derived from the M8084 military design.
Two or more elements in a single envelope were handled by adding letters after the heater identifier, in alphabetical order, so an ECH35 is a 6.3 volt heated triode plus a hexode with an octal base; a PABC80 is a noval 300mA series-heater combination of 3 low-power diodes (two sharing a common cathode), plus a triode.
Mullard initially handled semiconductor naming by using the "O" heater code (shifting "Cold Cathode" to a code of "Z"), but from 1966 the new Pro Electron standard codified the allocation of type numbers for solid-state active devices by using initial letters "A", "B" and "C" (rarely used heaters) for germanium, silicon and other semiconductor diodes and transistors. Other letters were allocated for for integrated circuits. Heater letters A, B, C, F, K, V and Y ceased to be allocated. This meant that most existing European valve type number allocations were compatible with the new system, but sometimes ambiguities could only be resolved by checking the digits in the name. For example, it might not immediately be obvious whether a (hypothetical) AD108 is a 4 volt power triode or a germanium power transistor; an AZ41 (still on sale in the 1970s[1]) might be thought to be a germanium Zener diode (although, with only 2 digits for the serial number, it was not really a valid Pro Electron designation). By the time of the introduction of the Pro Electron series most tube names started with either D, E, G, P or U, so confusion between the two systems was unlikely.
- 1st letter: Heater rating
- A 4V
- B 180mA AC/DC
- C 200mA AC/DC
- D 0.5–1.5V (normally 1.4V)
- E 6.3V AC
- F 12.6V car battery
- G 5V or miscellaneous
- H 150mA AC/DC
- I 20V
- K 2V DC
- L 450mA AC/DC
- O Cold cathode (by 1955 this also included semiconductors as these had no heater)
- P 300mA AC/DC
- T 7.4V; Misc.
- U 100mA AC/DC
- V 50mA AC/DC
- X 600mA AC/DC
- Y 450mA AC/DC
- Z Cold cathode
- Remaining letters: Type(s) of device(s)
- A diode (excluding rectifiers)
- AA double diode with separate cathodes (excluding rectifiers)
- B double diode with common cathode (excluding rectifiers)
- C Triode (excluding power and gasfilled triodes)
- D Power triode
- E Tetrode (excluding power valves)
- F Pentode (excluding power valves)
- H Hexode or Heptode (of the Hexode type)
- K Octode or Heptode (of the Octode type)
- L Output tetrode, beam tetrode or pentode
- M Tuning indicator
- N Gas filled triode or thyratron
- P Tube with secondary emission system
- Q Nonode (also called Enneode[2])
- S TV sync oscillator
- T Beam tube or miscellaneous
- W Gas rectifier
- X Gas fullwave rectifier
- Y Halfwave rectifier
- Z Fullwave rectifier
- Figures: Base type & serial number
- 1-9 Various side contacts, octals, specials (exceptions are ECH3G, ECH4G, EK2G, EL3G, KK2G which have octal bases)
- 10–19 8-pin German octal
- 20–29 Loctal B8G; some octal; some 8-way side contact (Exceptions are DAC21, DBC21, DCH21, DF21, DF22, DL21, DLL21, DM21 which have octal bases)
- 30–39 International Octal (IEC 67-I-5a)
- 40–49 Rimlok B8A
- 50–59 B9G; Loctal B8G; Octal; 3-pin glass; Disk-seal; German 10-pin with spigot; min. 4-pin; B26A; Magnoval B9D
- 60–69 B9G; some submins
- 70–79 Loctal Lorenz; wire submins
- 80–89 Noval B9A (9-pin; IEC 67-I-12a)
- 90–99 B7G (miniature 7-pin; IEC 67-I-10a)
- 100–109 B7G; Wermacht base; German PTT base
- 110–119 8-pin German octal; Rimlok B8A
- 130–139 Octal
- 150–159 German 10-pin with spigot; 10-pin glass with one big pin; Octal
- 160–169 Flat wire submins; 8-pin German octal
- 170–179 RFT 8-pin; RFT 11-pin all glass with one offset pin
- 180–189 Noval B9A
- 190–199 B7G
- 200–209 Decal B10B
- 230–239 Octal
- 270–279 RFT 11-pin all glass with one offset pin
- 280–289 Noval B9A
- 300–399 Octal
- 400–499 Rimlok B8A
- 500–529 Magnoval B9D; Novar
- 600–699 Flat wire-ended
- 700–799 Round wire-ended
- 800–899 Noval B9A
- 900–999 B7G
- 1000- Round wire-ended; special nuvistor
- 2000– Decal B10B
- 3000- Octal
- 5000- Magnoval B9D
- 8000- Noval B9A
For signal pentodes, an odd numerical identifier most often identified a variable transconductance (remote-cutoff) valve whereas an even number identified a 'high slope' (sharp-cutoff) valve.
