Mullard–Philips tube designation


In Europe, the principal method of numbering vacuum tubes was the nomenclature used by the Philips company and its subsidiaries Mullard in the UK, Valvo in Germany, Radiotechnique in France, and Amperex in the United States, from 1934 on. Adhering manufacturers include AEG, CdL, CIFTE, EdiSwan, Lorenz, MBLE, RCA, RFT, Siemens, Telefunken, Tesla, Toshiba, Tungsram, and Unitra . This system allocated meaningful codes to tubes based on their function and became the starting point for the Pro Electron naming scheme for active devices.

Nomenclature systems

The system allowed for cross-referencing with the American RETMA tube designation, the Marconi-Osram tube designation, and with military numbering systems such as civilian valve numbering in the United Kingdom and the Joint Army–Navy tube designation in the US.
European tube manufacturers agreed on the system, but in the UK, MOV, STC/Brimar 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", used all American designations. STC/Brimar was a UK subsidiary of the American giant ITT.
Special quality tubes were sometimes identified by placing the numerical part of the designation between the heater rating and the tube type. The special quality could be anything, from rugged designs for military and industrial use, through devices with exceptionally low noise and microphony, to designs primarily optimised for long life without cathode poisoning when used for switching in a digital computer. For example, an ECC81 manufactured as a special quality tube would usually be designated 'E81CC'. The system was not universal as other special quality designation systems existed. An EF91 in its special quality version was designated 'M8083' as in this case the standard EF91 was derived from the M8083 military design. Also, the SQ tube was not always designed for the same tasks or given the same Maximum Ratings 6.3V dual triodes.
It was the usual practice for power transformers to have a 5 volt insulated winding for rectifier filaments, and a 6.3 volt winding for all the other heaters; virtually all valves with 5V filament are rectifiers with cathode connected to heater, in practice full-wave, e.g. GZ34. For lower-voltage lower-power requirements, rectifiers with 6.3V heaters and insulated cathodes such as the EZ80 were used, connected to the common filament supply. There is no special nomenclature for EHT rectifiers for cathode-ray tubes; the EY51 and EY86 were rated at 17kV with an average current of 350 microamps. The GY501 is another example. In practice most "xY" half-wave rectifiers are EHT types; but there are plenty of exceptions.

Symbol definitions

  • 1st letter: Heater rating
  • Remaining letters: Type of device
  • * All except special-quality "Z" cold cathode tubes:
  • **A Low-current diode
  • **AA Low-current double diode with separate cathodes
  • **B Low-current double diode with common cathode
  • **C Small-signal vacuum triode
  • **D Power triode
  • **E Small-signal tetrode
  • **F Small-signal pentode
  • **H Hexode or Pentagrid converters of the Hexode type. Also Hexodes that have an additional suppressor grid making them a Heptode of the octode type but that do not operate on the pentagrid principle.
  • **K Octode which is always a Pentagrid converter. Also a Heptode of the octode type and which operates on the pentagrid principle.
  • **L Power tetrode, beam tetrode or power pentode
  • **M Tuning indicator
  • **N Gas-filled triode or thyratron
  • **P Tube designed for secondary emission
  • **Q Nonode
  • **S TV sync oscillator
  • **T beam tube, or miscellaneous
  • **W Gas-filled halfwave rectifier
  • **X Gas-filled fullwave rectifier
  • **Y Halfwave rectifier
  • **Z Fullwave rectifier
  • '''Numbers: Base type and serial number'''

Single-digit numbers

The first types assigned using this sequence were less systematic and sometimes would append the US "G" and/or "GT" suffixes for octal base versions, although the base type was not always knowable from just the type number:
  • KK2 was a pinch-type valve fitted with an American 7-pin base.
  • Sometimes special versions were made with US bases with no change in the type number, but
  • in the case of Octal (IO) often a "G" would be appended to the type number; examples are ECH3G, ECH4G, EK2G, EK2G/GT, EL3G, EL3NG, KF3G, KK2G and KL4G.
  • EBF2Gm EBF2GT/G and EBF35 had International Octal bases but European base connection sequences.
  • Versions without the pinch at the top and/or with a metal screen might have "N" appended, and letters "A", "B" or "X" would sometimes be used for variants. The AL2X differs from the AL2 in connecting the control grid to pin 6 instead of the top cap. EL33, EL33A and EL33B are octal power pentodes differing only in whether metallization shielding is connected to pin 1 or 8.
  • The AL3, AL4, EL3N and EL3NG have identical characteristics to the EL33, EL33A and EL33B but with different heater voltages and/or bases; the CL4 and CL33 are lower voltage and lower power devices that are only somewhat similar to the EL33 and PL33.

Historical progression

The older Philips system

Prior to 1934, Phillips numbers were based on a sequence of one letter to indicate filament current range, followed by one or two digits for the filament voltage, then two digits that gave either the amplification factor or a code beginning with 41 to indicate tetrodes, pentodes and so on. Examples are:
  • A409
  • B2043
  • C243N.

Single-digit numerical sequences

An example of this format is "CL4". This format was used from 1934, when many European-specific bases existed. These bases included 5- and 8-pin side-contact, and 4- to 7-pin alternatives to incompatible US base types. At this time there was pressure to produce devices compatible with wider markets, and so several versions of the same device might be produced with different bases, yet sometimes no change in type number.

Double-digit numerical sequences

An example of this designation format is "EL33A". After about 1938 the digits gave a more consistent definition of the base type. During the 1950s, most often two devices that shared the same number and all but the first letter of the name would be very similar except for heater voltage/current. During this time older filament voltage and current "families" were abandoned, so a device name beginning with "A", "B", "C" or "K" and ending in two or more digits is very unlikely to be part of this naming scheme. For example, the "KT61" is not a 2 Volt-filament beam tube within the Philips naming system, but a "kinkless tetrode" within the Marconi/EMI naming scheme.

Triple-digit numerical sequences

Examples of this format are "PL302" and "EF183". From about the start of the 1960s an extra digit was needed for new devices. Either a digit 1 was inserted before the 8 or other base-defining digit, or a three-digit sequence was used. For example, a PL500 is a power pentode in a Magnoval base.

Four-digit numerical sequences

Numbering using four digits were never issued under the Mullard-Philips scheme. They were obtained from the successor scheme, Pro Electron.

Semiconductors

Mullard initially handled semiconductor naming by using the "O" heater code. The second letter broadly indicated the type of device, roughly following the tube designation, without indicating the semiconductor material:
  • A low-power semiconductor diode, e.g. OA7
  • C transistor, e.g. OC26
  • Y rectifier diode, e.g. OY110
From 1966 the new Pro Electron standard codified type numbers for solid-state active devices using initial letters "A", "B" and "C" for germanium, silicon and other semiconductors. Other letters were allocated for integrated circuits. Heater letters A, B, C, F, K, V and Y ceased to be allocated for electron tube devices.
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 AD108 is a 4 volt power triode or a germanium power transistor; an AZ41 might be thought to be a germanium Zener diode. 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.