Together with the "B4N"-set a universal 2-tube receiver 0-V-2 of "PL-2"- type was produced. It could operate as both one- or two-tubed. Besides, in its construction usual "micro"-tubes and two-grid tubes of MDS-2 type could be used, the latter working on low anode voltage.

In all the above-mentioned receivers tubes of direct heating were installed. The output of radio model "DLS-2" was the first attempt to make net-supplied receivers. It is a device with a crystal detector combined with a 2-tube audio amp and a vacuum rectifier. It works using UO-3 tubes of direct heating. The output of tubes with indirect heating was the beginning of a new era in development of radiotechnics because then the problem of complete sourcing of radios from AC net was solved.

Among the first receivers of this type one can mention radio "E4S-2" of Orjonikidze Works ("Screened 4-tube AC-sourced") constructed by E.N.Genishta and radio "EKL-4" of Kozitsky Works (Leningrad). In both new tetrode tubes were applied. The further improvement of the former became radios "E4S-3" and "E4S-4" and of the latter - radio of "EKL-34" type. All those AC receivers were assembled according to the structure of direct amplification 1-V-2 using 4-volt glass tubes of indirect heating types SO-124 and SO-118. A triode UO-104 of direct heating was used in audio output. Those receivers enjoyed a wide spread among urban listeners. Just to mention also radios "5NR-3" and "RP-8" with the schematics similar to the above. The "U4S-1" set of Ukrainian make was also known.

In 1934 the Orjonikidze Works produced a battery-supply receiver "BI-234" ("Battery Individual") which gained a wide popularity among the rural listeners. A similar radio named "RPK-9" was later produced by Leningrad "Radist" Works. The difference was  in their outlook.. The peculiarity of the set was that it could work using not a full set of tubes. Depending on their quantity the set could be switched on in the configurations 1-V-1, 1-V-0, 0-V-1 or 0-V-0. The mode of reception was set by replacement of the bridges. Its modifications are known to be the "RPK-10" and "RPK-11" .

In 1935 the same Orjonikidze Works produced a new AC-radio "SI-235" ("AC-supply Individual" - constructed by P.A.Lokhvitsky), wich soon became the most numerous receiver among the urban listeners of the USSR. With this radio the era or direct amplification receivers ends. They were followed by multi-band superheterodynes - the ancestors of modern radio receiving systems.

In 1930's  the output of cheap crystal radios continued. Among them there were the  "DV" , "P-8" and some others.

BT

B4N

E4S-2 with "Rekord"   speaker

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