This valve is labelled VT-31 as an American service code but was made as a UK VT31. The Mullard commercial equivalent is the SG250 and Ediswan use the Type designation ESG250. With the advent of the CV designations in 1941 the RAF VT31 became the CV1031.
The American VT-31 (commercial Type 31) is a triode on a UX4 base - quite different.
Our guess is mid 1930s for its design date. The output is probably in the low HF region.
The American VT-31 (commercial Type 31) is a triode on a UX4 base - quite different.
The lettering on the balloon is quite clear including the old stores code of 10E/8739.
Here at the anode end the two grids can be seen. Both are corroded as the vacuum is no longer present. In the centre are the ceramic supports for the top loop of the filament.
The corrosion on the anode and part way along the grids.
The connection end of the filament.
The balloon envelope is 160 mm in diameter and is 360 mm tall.
