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T-104 Multivibrator Integrated Early Computer Germanium Transistor Diode Circuits

OddMix.com - Transistor Technology Note - 080801 - Karl Nagy

Fig. 1 - T-104 Multivibrator module [6 KB]
Fig. 1 - T-104 Multivibrator module

Toward the end of 1955, RCA Corporation delivered to the U.S. Army Ordnance Tank and Automotive center in Detroit Michigan their first Bizmac/ENIAC System, at that time the smallest and largest digital data processing system ever made. The computing giant contained 32,000 vacuum tubes and 600,000 additional components and took three years of effort to design and build. It had an amazingly good uptime of 96%. In spite this demonstrated great reliability at least by tube technology standards, in about six years time the Bizmac was replaced by a smaller and yet more powerful design. Rapid progress at the time made obsolete every glamorous new machine in every five to six years time.

Newer computer designs demonstrated that it was most important to reduce the size and power consumption of the newer computing machines and their components. As a result of size reduction dual and miniature tubes were invented and used. Part reduction was difficult at best since each decade counter subassembly required a minimum of four flip-flop circuits, each having two single or one dual triode. The computer architect's excitement increased in earnest with the discovery and availability of the new solid state semiconductor devices.

Fig. 2 - T-104 Multivibrator schematics [7 KB]
Fig. 2 - T-104 Multivibrator schematics

Diodes and transistors has a great advantage over the electron tubes that they do not require power for a heater as semiconductors have no such component. Tubes usually require a few watts of power to keep their cathode hot enough for proper operation. When a machine uses thousands of vacuum tubes, the power and the extra heat dissipated added up in a hurry. And tubes require high voltages for their operation along with high voltage capacitors and other components. The Bizmac computer had a 18.75 ratio of tubes versus other components. Assuming two Watts power for each of the 32,000 vacuum tubes, Bizmac's filament heater circuits alone consumed about 64,000 Watts of power for each hour of operation! By comparison an average home uses about 1-3,000 Watt hours of electrical power each day.

The T-104 multi-vibrator made by Engineered Electronics Co Fig. 1. It's schematic shows that the T-104 circuit contained not less than two transistors, two diodes, four capacitors and ten resistors Fig. 2. In a single vacuum tube size metal container, it had a total of eighteen components, and the assembly could be inserted into a standard nine pin miniature tube socket. Every computer at the time used hundreds of multivibrators in their different parts.

                     Parts list for T-104 Multivibrator Circuit Assembly

                         Q1, Q2     - Transistor, 2N404, Germanium, PNP 
                         C1         - Capacitor 270 pF
                         C2, C3     - Capacitor 68 pF
                         C4         - Capacitor Electrolytic 22 uF, 6VDC
                         D1, D2     - Diode, 1N191, Germanium, Signal
                         R1, R5, R8 - Resistor 27 K, 0.25 W, CC
                         R2         - Resistor 12 K, 0.25 W, CC
                         R3         - Resistor 3.3 K, 0.25 W, CC
                         R4, R9     - Resistor 2.2 K, 0.25 W, CC
                         R6, R7     - Resistor 22 K, 0.25 W, CC
                         R9         - Resistor 2.2 K, 0.25 W, CC
                         R10        - Resistor 560, 0.25 W, CC
                         P1         - 9-Pin Miniature Tube Header with Case

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