The GU-50 (Cyrillic: ГУ-50) is a power pentode intended for 50 Watt output when operated as a linear RF amplifier at frequencies up to 120 MHz. The design and build quality was for Russian mobile military equipment. The knob, or handle, on the top and moulded glass key allow for rapid replacement in the field.
The GU-50 is a Soviet made copy of the German Telefunken LS-50 power pentode.
Currently (2014) this valve has been used in hi-fi audio amplifiers, both in single-ended and push-pull designs. The base is a non standard design.
The aluminium cap and handle are electrically isolated from the valve itself. This view is looking along the length of the grids with the suppressor grid support visible through the gaps in the anode. The side flanges with the stitched seam is placed in the centre of the working face for best heat removal.
The working face of the anode. The glass key can be seen on the right. Various forms of valve holder were made including metal cylinders with lids to cover the top handle.
The all glass construction the evacuation tube would be located at the top of the envelope. The glass locating key is clearly visible in this image.
The top of the valve with aluminium cap and plastic knob or handle.
The wide glass tube envelope is 40 mm in diameter, and excluding the base pins is 93 mm tall.
References: Datasheet & wikipedia. Type GU-50 was first introduced in 1971.