ML4, PA1, AC/P, 41MP, TT4, LF4, 41MXP, AC/P1, 054, CV1689, CV1161, CV1458, SMALL SIGNAL, B5

The ML4 B4 based output triode, first introduced by Osram in 1929 is descended from the first of its type - the KL1 of 1926 and like its elder sibling it was primarily a professional and military type, little used in domestic applications.

It finds favour as a single valve phase splitter and as an inter-stage drive valve for output valves such as the PX4 and PX25 triodes.