The LS50 is RF power pentode for aircraft use at frequencies in the VHF range. The anode dissipation is 40 Watts and in Class C the output power at the highest frequencies was 40 Watts and at lower frequencies the output could rise to 85 Watts.
The GU-50 is a post war Russian copy of this German valve.
The metal top is threaded to take a Bakelite handle. The valve plugged into a screened holder with a flap on the front panel. This allowed service in-situ.
The valve was tested and accepted at BAL716 and the other lettering indicates the government owners.
The serial number down the glass.
The anode with considerable surface area has a slot at the end of the grid axis that reveals the support for g3.
The solid hard glass pins fixed into a hard glass base. The central spigot covers the evacuation pip and has been cemented into place.
The wide glass tube envelope is 37 mm in diameter and, excluding the base pins, is 92 mm tall.
Reference: Data-sheet. Type LS50 was first introduced in 1941.