It's the output pentode of the new series of indirectly heated tubes for DC mains operation with standardized 180 mA heater current. Simultaneously it was the first indirectly heated output tube in continental Europe. It was available in 3 base versions.[Jacob Roschÿ, 2003-01-22]
Babani, International Radio Tube Encyclopaedia p. 254 & 255
Philips Bulletin Philips Österreich Preisliste Dezember 1931
Taschenbuch zum Röhren-Codex 1951
L'ABCDaire des lampes de TSF des jeunes années
