Can anyone ID this thing or give me any info?
It's a directly heated triode for battery operation, I think.
The 'M.E.C. TEST' label colouring reminds me of GEC/Osram
labels but that may be just coincidence. Does anyone know
what MEC test is? I thought this might be a hearing aid
valve, but most of the later wired in ones were pentodes
ISTR and all the examples of early thermionic hearing aids
I can find on the web use wire ended valves - DF5x series
or U.S. equivalents. The base is not B4/British 4 pin but
a much smaller thing.
It arrived in a box of junk from a radio rally/ham fest.