. The Bell System technical journal . ipment have progressed, 254 THE BELL SYSTEM TECHNICAL JOURNAL, MARCH 1956 Table I—Transistor Characteristics Code No. Type and Filling Alpha Max. Ico at 28Vand 65°C Emitter ZenerVoltage at 20^=1 M1868M1887 p-n-p Oxygenn-p-n Vacuum .75 150 Ma100 Ma >735>735 considerable progress has been made in improving transistors of Table I summarizes the characteristics of these transistors. For directing and analyzing the pulses, the control employs semicon-ductor diode gate circuits. The semiconductor diodes used in thesecircuits are of t
. The Bell System technical journal . ipment have progressed, 254 THE BELL SYSTEM TECHNICAL JOURNAL, MARCH 1956 Table I—Transistor Characteristics Code No. Type and Filling Alpha Max. Ico at 28Vand 65°C Emitter ZenerVoltage at 20^=1 M1868M1887 p-n-p Oxygenn-p-n Vacuum .75 150 Ma100 Ma >735>735 considerable progress has been made in improving transistors of Table I summarizes the characteristics of these transistors. For directing and analyzing the pulses, the control employs semicon-ductor diode gate circuits. The semiconductor diodes used in thesecircuits are of the silicon alloy junction type,^^ Except for a few in the gas tube circuits most diodes have a breakdown voltagerequirement of 27v, a minimum forward current of 15 ma at 2v and amaximum reverse current at 22v of 2 X 10^^ amp. 4. new techniques employed The concentrator represents the first field application in Bell Systemtelephone switching systems which departs from current practices andtechniques. These include:. Fig. 2 — Transistor packages, (a) Diode unit, (b) Transistor counter, (c)Transistor amplifiers and bi-stable circuits, (d) Five trunk unit. REMOTE CONTROLLED LINE CONCENTRATOR 255 1. High speed pulsing (500 pulses per second) of information betweenswitching units. 2. The use of plug-in packages employing printed wiring and encap-sulation. (Fig. 2 shows a representative group of these units.) 3. Line scanning for supervision with a passive line circuit. In presentsystems each line is equipped with a relay circuit for detecting call orig-inations (service requests) and another relay (or switch magnet) forindicating the busy or idle condition of the line, as shown in Fig. 3(a).The line concentrator utilizes a circuit consisting of resistors and semi-conductor diodes in pulse gates to provide these same indications. Thiscircuit is shown in Fig. 3(b). Its operation is described later. The pulsesfor each line appear at a different time with respect to
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