The VS10G is a high speed counting tube and was developed in about 1950.
By using a beam of electrons that were controlled by a powerful static magnetic field and dynamic electric fields, speeds of 1 MHz or more were possible.
The trade name Trochotron is derived from the shape of the spiral beam of electrons within the electric and magnetic fields. The central glass valve is surrounded by a powerful ring magnet cemented into place. The plastic base ring and top dome are cosmetic.
These valves are very sensitive to distortions in their internal magnetic fields and this warning was typical of all Beam-X tubes.
The envelope is 42 mm in diameter, and excluding the B26A base pins is 75 mm tall.
Reference: Data-sheet. Type VS10G was first introduced in 1950.