in the marking, which was usually a factory number of design, served for
division of the valves of the same category. According to this
system the valves models R-5, "Micro", MDS, PT-19, KT-2
were renominated as P-7, PT-2, ST-6, ST-19 and VT-14 (in Russian
In early 1930's
a series of economical glass valves
of 2 and 4V direct heating appeared (UB-107, UB-110, SB-154 etc.). The receivers using such valves were
battery-supplied. From 1935 the so-called 4-V "super"-series of glass valves with indirect heating appeared ,
which was installed in the AC-supply direct-amplification radios
(E4S, EKL) and in the first Soviet superheterodynes (TsRL). In 1931 the first
home penthode SO-113 of this series was produced.
The main drawback of this marking
system was that it defined the valves rather approximately. For
instance, one and the same valve could be referred to the category
of both receiving and amplifying valves. From the other side,
the valves that strongly differ from one another, such as triodes,
tetrodes with "cathode grid", tetrodes with a screening
grid, AF penthodes and both kinds of RF penthodes ("varimu"
and with short characteristics) were put into the same category
("C") of special valves. Produced in 1937 penthode model
SO-183 and a double diode-penthode SO-193 were also included in
the same category. Besides, the existing system of marking did
not make it possible to define if a given valve was used in a
battery radio or it had an indirect heating cathode.
In 1937 our electro-vacuum industry
started mass production of quite a new type of valves. There were
the tubes in metallic cases - 6A8, 6G7, 6J7, 6K7, 6L7, 6F5, 6F6,
6S5, 6X6, 5C4 (in Russian transcription) and also the glass electronic
optical tuning indicator 6E5 - similar to the contemporary American
tubes (6A8, 6Q7, 6J7, 6K7, 6L7, 6F5, 6F6, 6C5, 6H6, 5Z4, 6E5).
The metallic valve 6L6 (Russian AF power tetrode) and the glass
versions of the 5Z4 and 6L6 tubes were produced somewhat later
and still later the cheaper glass analogues of many other metallic
valves appeared. The marking system of all those valves was more
precise than that of 1929. The name of the valve was shorter and
its purpose and properties were defined more exactly.