Possible replacement = 1F5G. See also 1L5GU. Information from Stuart Irwin, Australia: The 1M5G and the 1L5G are two of a series of ruggedised valves produced by AWV for Australian conditions. The US and European battery valves then available often did not survive transport over the very bad country roads of the time. They also had good performance and longer life that the others but needed a higher filament current.
