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2N404 Projects

Some transistors classified as switching in the GE Transistor Manual 3ed include: 2N123, 2N167, 2N240, 2N393 – 2N398, 2N404, 2N425 – 2N450 and many others.  Elsewhere, these same transistors might be classified as binary, computer, digital or logic types.  The 2N404 seems to have been the best known to students and hobbyists.

IBM and others often applied their own numbering systems to switching transistors.  Many hobbyists first encountered switching transistors when buying industrial surplus logic and computer cards.  The transistors from such cards usually exhibited characteristics similar to 2N-series switching transistors

The most common digital hobby circuit seems to have been the astable multivibrator such as the variations found in Gernsback Library's Transistor Techniques.

Sylvania's Performance Tested Transistor Circuits contains typical applications.

As do General Electric publications.
Monostable multivibrators found application as timers and delays.

Bistable multivibrators saw less use.  See GE Transistor Manual 3ed, page 88.
Sylvania's Performance Tested Transistor Circuits contains a flip-flop composed counter.  Electronics Illustrated for January 1960 contains a detailed article on binary adding, subtracting, multiplying and dividing using Sylvania's counter.

More generally, a group of flip-flops (bistable multivibrators) working together were called a "register."  Typically, a register held data or an instruction long enough for logic circuits to decode or operate on the register contents.  A computer would contain such registers as a program counter (that pointed to the next instruction to be read and executed), an instruction register (that held an instructions being decoded by logic circuits), a memory buffer (which held the latest data retrieved from memory), an accumulator (which held data undergoing an arithmetic or logical operation), a condition register (which held the results of tests performed on data) and others.

Boolean algebra (computer logic) can be implemented in many technologies:  mechanical, hydraulic, relays, thermionic tubes, transistors and still more.  During the 1950s and 1960s many articles used vague approximations to practical circuits or gas tubes and relays.  The half dozen "logicians" Steven exchanged ideas with preferred to work with transistors.  This preference led to our getting most of our information from booklets and books.

Sylvania's Performance Tested Transistor Circuits booklet provides an example of a NOR (logical "or" followed by logical "not" or "invert") circuit.  This circuit is implemented in discrete diode-transistor logic (DTL).

General Electric's transistor manuals offer a resistor-transistor logic (RTL) NOR

In Design of Transistorized Circuits for Digital Computers Abraham Pressman provides worked examples producing DTL and RTL logic circuits.

Digital Equipment Corporation's Logic Handbook used some off-beat (to communications types) symbols.  But it is worth understanding.  DEC also provides System Module Schematics and the Computer Lab Workbook earlier editions of which served as prototypes for hobby logic laboratories.  DEC gave their users new editions each year.  So professionals and graduate students handed their copies down to technicians and undergraduates who handed their older copies down to hobbyists.

Transistor types 2N167, 2N229, 2N404 plus IBM and Polaris R212 may be purchased from the Transistor Museum Store.