Dating mullard valves
Fleming's patents for the very first electronic valve. The manufacturer is important as well as the valve type, since valves with the same type number from different manufacturers may vary significantly. These books all contain full page sheets on each valve covered with at least one curve for each valve.
I have made a full table of manufacturer recommended substitutions with links to PDF data sheets, where available. The complete index has an ordered table of all the valves covered in these books with links to their data sheets as full page PDF files.
Each book also has short data on some obsolescent types, circuits, articles on construction and lists of valve sets for commercial radios and kits.
The This Cossor manual has interesting articles on: valve fundamentals; valve construction and valve types as well as full page descriptions with curves of sixty valve types.
Heater and cathode life was poor and good working specimens are uncommon.
I know this has been discussed here before, but I've misplaced my hard copy of how to decipher this. In the case of the 1st letter, ie 'B' for xf2 that's the factory code, xf1=Blackburn, xf2=Blackburn -or- Eindhoven, Holland.
There are acorns, nuvistors, electrometer tubes, barreters, time delay relays and laboratory and test samples. A timeline of the development of valves and broadcasting in the U. A history of Mullard with some pointers on dating the PM series valves. Some compilations have been found to be unreliable, particularly about equivalences.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 .A fairly large selection ( The gallery of optoelectronics contains all the vacuum and gas-filled valves used for display or light detection.Included are tuning indicators, photocells, flash tubes, a vidicon and a photomultiplier. Howe on the fiftieth anniversary of Fleming's invention of the first electronic valve.
In a separate cartouche there often is a two character alpha code which denotes manufacture date eg AA.