Valves used by the British military Armed Services were marked with a CV or common valve name which was defined by the Inter-Service Technical Valve Committee in 1941. Often, below the CV number, a two part alpha code of the form KB/xx or JB/xx will be seen which gives the devices manufacturing specification and qualification . For the first part of the alpha code, the K designates a valve manufactured to specification K1001 or K1006; similarly a J designates a valve manufactured to a JAN or MIL spec. The second letter of the first part of the alpha code describes the qualification approval the valve type has, a B denotes qualification by a UK authority, a U denotes US qualification, a D denotes Australian qualification and an X denotes Director of Electronics Research and Development (DERAD) approval.
The second part of the alpha code identifies the factory that manufactured the device, the most commonly seen codes and their corresponding manufacturers are:-
| A | Mullard, Blackburn, pre Jan 1951 |
| A | Thorn, Tottenham, pre April 1964 |
| AB | Sylvania-Thorn, Enfield |
| AC | Brimar - Thorn-AEI, Footscray |
| AD | Brimar - Thorn-AEI , Rochester |
| B | Edison Swan, Baldock, pre Sept 1945 |
| BA | AEI, Woolwich |
| BC | Joseph Lucas, Birmingham |
| C | Edison Swan, Ponders End, pre Sept 1951 |
| CC | Cathodeon, Cambridge |
| CE | 20th Century Electronics, pre March 1957 |
| CF | 20th Century Electronics, New Addington |
| CN | Pye Industrial Electronics |
| CO | Newmarket transistors, Newmarket |
| CS | Cathodeon, Southend |
| D | Mullard Radio Valve Co., Mitcham |
| DA | Mullard Radio Valve Co., Blackburn |
| DB | Mullard Radio Valve Co., Salford |
| DC | Mullard Radio Valve Co., Whyteleafe |
| DE | Mullard Radio Valve Co., Fleetwood |
| DF | Mullard Radio Valve Co., Waddon |
| DG | Associated Semiconductor Manufacturers, Southampton |
| DH | Societe Anonyme Philips, Brive, France |
| DJ | Wiener Radio Werke, Abbeygasse 1, Vienna |
| DK | Philips GMBH, 140 Ebentalstrasse, Klangenfurt |
| DL | NV Philips Gloeilampenfabrieken, Nijmegen |
| DM | NV Philips, Stakskanaal, Holland |
| DN | La Radiotechnique, Caen, France |
| DP | Valvo GMBH, Hamburg, Germany |
| DQ | Philips SpA, Milan, Italy |
| DR | Philips AG, Zurich, Switzerland |
| E | Thorn-AEI, Brimsdown |
| EA | Edison Swan, Ponders End |
| EB | Edison Swan, Gateshead |
| EC | Edison Swan, Tottenham |
| EN | Thorn-AEI, Sunderland |
| F | STC, Paignton |
| FB | STC, Footscray |
| FC | STC, Lorenz,. Esslingen, Germany |
| FD | STC, Rochester |
| FDA | Alexandria, NSW, Australia |
| FE | STC, Oldway (Additional to Paignton factory 'F') |
| FF | STC, Harlow |
| G | Ericsson, Beeston |
| GA | (Ericsson), AB Svenska Elektronror, Stockholm, Sweden |
| H | Hivac, Harrow |
| HC | Hivac, Chesham |
| HR | Hivac, Ruislip |
| J | STC, Crewkerne, pre Jan 1946 |
| J | Radar Electronic Equipment |
| JA | SGS Fairchild, Ruislip |
| JB | SGS Fairchild, Agrate, Milan, Italy |
| JD | Elliott Bros. (London) Ltd, Borehamwood |
| JE | Elliott-Litton, Borehamwood |
| JK | La Radio Technique, Suresne, Paris, France |
| JN | International Rectifier Co., (GB) Ltd, Oxted |
| JQ | Associated transistors, Ruislip |
| JT | Microwave Associates Ltd, Luton |
| K | Electronic Tubes, High Wycombe |
| L | CSF, Levallois-Perret (Seine), Paris, France |
| L | MOV Highgrove pre Oct 1951 |
| LB | CSF, St. Egreve, Grenoble, Isere, France |
| M | Gramophone Co., Hayes |
| MA | EMI research labs, Hayes |
| MB | EMI research labs, Ruislip |
| ME | EMI, Hayes |
| MR | EMI (Valve Division), Ruislip |
| MT | EMI, Treorchy |
| N | Nore Electric, Southend |
| N | STC, Footscray, pre August 1951 |
| NP | Texas Instruments, Dallas Road, Bedford |
| NQ | Texas Instuments, Bedford |
| NR | Texas Instruments, Nice, France |
| O | Rank Cintel, Lower Sydenham |
| OR | Rank Cintel, Rotunda |
| OS | Rank Cintel, Sidcup |
| P | Philips, Eindhoven, Holland |
| P | GEC, Shaw, pre August 1948 |
| PA | Philips Teleindustri, Stockholm, Sweden |
| PDA | Philips, Hendon, Australia |
| Q | English Electric Valve Co., Chelmsford |
| QB | Marconi Wireless Telegraphy Co., Great Baddow |
| QC | Marconi Wireless Telegraphy Co., Chelmsford |
| QD | English Electric Valve Co., Stafford |
| QE | English Electric Valve Co., Kidsgrove |
| QF | English Electric Valve Co., Nelson Research Labs, Hixon |
| R | Ferranti, Moston |
| R | Ferranti, Gem Mill Oldham, pre July 1947 |
| RA | Ferranti, Edinburgh |
| RB | Ferranti, Dundee |
| RC | Ferranti, Chadderton, Oldham |
| S | AEI, Rugby |
| SA | AEI, Lutterworth |
| SB | AEI, Lincoln |
| SC | CFTH, Usine de Joinville, Seine, france |
| SD | SESCO, Rue de L'Amiral, Mouchez, Paris, France |
| SDA | Amalgamated Wireless, Australia |
| SF | CFTH, Rue Mario-Nikis, Paris, France |
| SL | AEI, Leicester |
| SP | AEI, Peterborough |
| T | British Tungsram, Tottenham |
| U | MOV, Bulmer, pre Oct 1945 |
| U | Nucleonic and Radiological, Stratford |
| V | Cossor, Highbury, pre Sept 1945 |
| V | Gilbert Photoelectrics |
| VA | Westinghouse, Chippenham |
| VF | MCP Electronics, Alperton |
| VL | Hughes Internations (UK) Ltd., Glenrothes |
| VR | Brush Rothermell Crystal Co., Hythe |
| W |
GEC, Hirst Labs, Wembley ASM Ltd |
| WB | GEC, Coventry |
| WD | Claude General Neon Lights, Wembley |
| WE | ASM Ltd, Hazel Grove |
| WF | ASM Ltd, Broadstone |
| X | MOV, Springvale, pre Oct 1951 |
| Y | MOV, Moray, pre April 1945 |
| YA | Leigh Electronics, Havant |
| YC | Semiconductors Ltd., Cheney Manor, Swindon |
| YD | Semiconductors Ltd., Towcester |
| Z | MO Valve Company, Hammersmith |
| ZA | MOV, Gateshead, pre March 1957 |
| ZB | MOV, Perivale |
| ZC | MOV, Springvale, pre August 1957 |
| ZD | MOV, Dover, pre Dec 1956 |
| ZE | Osram GEC Lamp Works, MXT Dept, pre March 1957 |
In a separate cartouche there often is a two character alpha code which denotes manufacture date eg AA. The first letter denotes the year and uses the entire alphabet except for I and O and started in 1945. Hence an A denotes 1945 and Z denotes 1969. In a similar fashion the second letter denotes the month of manufacture with A denoting January and M denoting December.
An additional system of dating is also used which records the date of valve labelling, this dating system utilises a four digit numeric code in which the first two integers denote year and the second two integers the week of the year. Hence 6712 would denote March 1967.