Electron tube SG4S (СГ4C) is a soviet voltage regulator. Stabilized voltage in the operating current range: 152,5±7,5V. Operating current: 5-30mA. Filling: argon-helium. SG4S is direct replacement for the similar types OD3A, OD3 or VR150/30 (technical parameters are close to identical, OD3 and VR150/30 do have another bulb shape). Service life guarantee: not less than 500 operating hours. Original enclosed datasheet is available for download. New old stock tubes. Made in the 60's.