6C4P / 6U4P = EZ90 = 6Z31 tube. Dual channel kenotron
The 6C4P (6U4P) double kenotron with a common cathode has been designed for use as a low-power rectifier.Cathode: indirectly heated, oxide-coated.
Good quality, the Sound is nice!
All tubes new, military equipment and have "OTK" mark. Near equivalent: EZ90 and 6Z31 but have pinout different.
Cathode type: oxide, indirect heating
Envelope: glass, miniature
Mass, g: 15
Filament voltage, V: 6,3
Filament current, A: 0,54-0,66
Anode current, A: 0,15
Max.reverse anode voltage, kV: 1
All datasheets here.