IBM Pluggable Units
Pluggable units TR-56, D-11, IN-6, CF-1
IBM Pluggable Units
This is a project to document early IBM pluggable units
and an early training kit that uses them.
Two of these training kits have surfaced, one of them is in
collection, listed as "An unkown IBM vacuum tube treasure".
I now have one too, but Mark's is in better shape.
These are some of the first modular components
(or field replacable units) used in computers.
Each consists of (usually) one vacuum tube in a small chassis
consisting of the tube socket, two phenolic spacers and
a base with a 9-pin tube plug.
The spacers have 10 notches to hold component leads (wires) in place.
Resistors, capacitors and other components are wired between
the tube socket and the base.
Intermediate connections between components are made at the
spacers by bending the leads over to adjacent notches
and soldering to other leads.
Each unit has an insulated curved handle with an identifying code
stamped on the end.
The code consists of two letters and a number.
The two letters indicate what kind of circuit it is and the
number tells which variation.
Common letter codes are IN for inverter,
CF for cathode follower,
TR for trigger (flip-flop) and
D for diode.
Mark's training box came with this complement of modules:
- 1 CF-5
- 1 DS-1
- 1 DS-5
- 1 IN-5
- 2 IN-13
- 1 IN-34
- 1 PS-2
- 1 PS-25
- 1 TH-1
- 1 TR-1
- 6 TR-4
- 1 TR-6
- 1 TR-11
- 1 TR-31
The basic circuits are similar to those used in the
NORC built by IBM in the early 50's.
The logic levels are +10v and -25v.
This illustration is from Millman and Taub,
"Pulse and Digital Circuits", 1956 in the classic McGraw-Hill
Electrical and Electronic Engineering Series.
Pluggable units schematics
I once obtained a bag of IBM pluggable units
at an electronic surplus store.
Four of them are shown above.
I traced out the circuits and made individual schematics.
Mark Metzler has begun tracing his units, and I recently obtained
three more and traced them too.
Here are the drawings for the pluggable units in the
IBM 650. Note that these somewhat later units
are different, they have 10 pins at the base instead
of 9 and they use different supply voltages.
The supply voltages in the IBM 650 are indicated by numbers
in squares in the drawings. The voltages are as follows,
referenced to the number in the square.
- 1R. +250V for read
- 1W. +250V for write
- 2. +150V
- 3. +70V
- 4. -22V
- 5. -35V
- 6. +50V
- 7. -63V unregulated (protective bias)
- 8. -50V
- 9. -70V
- 10. -250V
- 11. +70V
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