History of the British Radio Valve to 1940 p. 150 & 200
Wireless World (The), London (WW, 79)
Babani, International Radio Tube Encyclopaedia
Taschenbuch zum Röhren-Codex 1948/49
TP4_Mullard: Telefunken Werkstattbuch
Wolfgang Bauer
Just Qvigstad
TP4_Mullard: My schematic collection.
Pier Antonio Aluffi