SI - 235
Production of the 4-tube receiver of direct amplification "SI-235" (AC-net , Individual, 2-coil, 3-tube without kenotron, of 1935 make) was started in 1935 at the Sergo Ordzhonikidze Works in Moskow. Head designer of the set was P.A.Lokhvitsky. Its prototype was the WL-231 set made by the "Telefunken G.m.b.H." The purpose of its production was creation of rather a cheap mass radio capable to compete with the 5-tube receivers "EKL-34" and "E4S-4" which were put out at the time. The "SI-235" was the last model of a direct amplification set that was produced in the USSR in big lots. In the author's collection the set has the serial number 00255.
BASIC TECHNICAL DATA.
Set of tubes: SO-148, SO-124, SO-122, VO-202 (VO-230)
MW 200-545 m; LW 714-2000 m
Power output 0.6 W
Power consumption 40 W
Dimensions 340õ420õ215 mm
The set is assembled in a case made of plywood with black "chagrene" covering (there were some sets covered with artificial leather). The removable back cover made of veneer with ventilating holes is fastened with two screws and gives access to the chassis with the tubes installed in one row. Unscrewing of the right screw disconnects the net current.
The tubes zone is divided into 2 compartments by the screening partitions. In the left one the AF tubes (SO-124 and SO-122) are set; in the right one the RF tube (SO-148). The VO-230 rectifier is put on the output transformer. The switching of the net tension of 110-127-220 V is made by reseting of the jumpers. On the chassis there are terminals for an adapter, aerial and ground. On the front side there are the controls of the set. In the center we can see a small tuning handle. In the window sized 25x30 mm a lighted vertical moving scale is located. On the scale window there is a small lever of the fine tuning for the RF anode coil while receiving. On the plastic framing of the window there is a casted round emblem of the works in the center and with the enscription by circumference: "The Head Administration of the Low-Voltage Industry".The lower left knob is a volume control. The right one is the positive feedback level control. Between them we see the band selector lever. The loudspeaker is of the dynamic type, with a paper diaphragm. The output transformer is installed on the speaker.
The set is designed according to the structure of direct amplification 1-V-1 with a changeable positive feedback on using tubes of the indirect 4-volt heating. The RF amplifier on the tetrode SO-124 has the cap coupling with the aereal. A SO-124 tube works as the detector. The AF amplifier is built on SO-122 penthode. The set is fed from the simple rectifier with VO-230 kenotron. All the resistors are carbonic ("Kaminsky" type). Inside some of them capacitors are located. The filter caps are paper-made and combined in the block under the chassis. The tuning cap has 2 sections with cellulose filmed isolator. The trimmers are made from two plates divided by a film. They tune by stretching the plates with a screw.