Variable-mu / remote-cutoff pentode. R (Russian: Р) – Double pentode or double tetrode. G (Russian: Г) – Combined triode-diode. B (Russian: Б) – Combined diode-pentode. F (Russian: Ф) – Combined triode-pentode. I (Russian: И) – Combined triode-hexode, triode-heptode or triode-octode. A (Russian: А) – Pentagrid converter. V (Russian: В) – Vacuum tube with secondary emission. L (Russian: Л) – Nonode. Ye (Russian: Е) – Magic eye tube (e.g. used as a tuning indicator). U (Russian: У) – Power triode (was soon deprecated). The 3rd element is a number – a series designator that differentiates between different devices of the same type. The 4th element denotes vacuum tube construction (base, envelope): P (Russian: П) – Small 9-pin or 7-pin glass envelope (22.5 or 19 mm in diameter). R (Russian: Р) – Subminiature glass envelope with a diameter up to 5 mm A (Russian: А) – Subminiature glass envelope (5 to 8 mm in diameter) with flexible leads. B (Russian: Б) – Subminiature glass envelope (8 to 10.2 mm in diameter) with flexible leads. G (Russian: Г) – Glass envelope (greater than 10.2 mm in diameter) S (Russian: С) – Glass envelope (greater than 22.5 mm in diameter), typically with an octal base. N (Russian: Н) – Nuvistor. K (Russian: К) – Metal-ceramic envelope. D (Russian: Д) – Glass-metal envelope with disc connections (for UHF operation). J (Russian: Ж) – Acorn tube For all-metal tubes the 4th element is omitted. The 5th element is optional. It consists of a dash ("-") followed by a single character or a combination of characters and denotes special characteristics (if any) of the tube: V (Russian: В) – Increased reliability and mechanical ruggedness (such as low susceptibility to noise and microphonics). R (Russian: Р) – Even better than V. Ye (Russian: Е) – Extended service life. D (Russian: Д) – Exceptionally long service life. I (Russian: И) – Optimised for "pulsed" (i.e. switching) mode of operation. K (Russian: К) – Vibration-resistant For instance, -YeV (Russian: -ЕВ) added after 6N2P (i.e. 6Н2П-ЕВ) signifies that this variant of the 6N2P has extended service life and low noise and microphonics. More often than not this means actual differences in internal construction of the tube compared to the "basic" type, but sometimes designators like -V and -I simply mean that the tube was specially selected for those characteristics from the regular-quality production at the factory. The new designation convention was