Brand : Siemens (& Halske, -Schuckert Werke SSW, Electrogeräte); Berlin, München 

Power/Output Triode 

Bi = 373_Triode = PTT100 = 3S22 = R115_Radiotechnique

Similar tube  KL70505

Other base   Bi/904 ; BiII

Other base and other heater:   Bi-spez ; BiIV

Multiple differences or of other kind:   REN904

Socket EU-Telephone 7-pin (G7K)

Filament heater Vf 4 Volt / If 1.1 Ampere / Indirect / Specified voltage AC/DC

Weitverkehrsröhre (Poströhre)