28 Oct
2007
28 Oct
'07
1:08 p.m.
Subject: Indicator tubes for transistor logic machines.
From: "Bob Shannon" <bshannon at tiac.net>
Date: Sun, 28 Oct 2007 14:03:43 -0400
To: "General Discussion: On-Topic and Off-Topic Posts" <cctalk at
classiccmp.org>
Is anyone familiar with vacuum tube indicators used on transistor logic
machines?
I recently found a small rack filled with small transistor logic modules.
Each module holds a flip flop or two at most.
The modules are small PC boards with a metal frame and handle. Test points
give you the state of each transistor
on the module.
Several modules have some sort of visual indicator tube as well.
These tubes are not much larger than a standard NE-2 bulb, but they more
resemble subminiature vacuum tubes.
The tubes are marked 01037 J3, each had four leads. Two of these leads
shows a resistance of 9.8 Ohms, and
appears to be a low voltage filament. One is grounded, the other is
connected to a bus in the rack of logic.
There is no 'getter flash' inside the glass tube, so they may be some sort
of glow discharge tube.
Looking at the insides of each tube thee appears to be a very fine V style
filament and a grid-like structure, but
I see no clear anode or plate structures. There are two thin 'wires'
outside of the grid, one in front and one
behind the central grid-like / filament structure.
The logic itself is made from 2N414 transistors, mil-spec at one time,
covered in conformal coating. Markings
show this device came from the USAF Airborne Instrumentation Labs. I only
have a small part of some
larger system, but I would like to power this rack of logic up and see these
indicators in action.
There is something very familiar about these things. They remind me of
something I may have seen once
in a telephone switching application when I was in the USAF long ago.
Any idea what these things may be? I'll try to get a digital photo, but the
tubes are mounted under small
metal clips with short leads.
They are vacuum florescent indicators. the anode (part that will glow)
is +V applied around 16-40V range and the cathode (most minus voltage)
is formed by the two wires that are a filliment (heater to some). Some
flavors of these also have a grid between the heater and the anode and
act like a triode vacuum tube in that if the grid is sufficiently
negative compared to the cathode/heater the tube will not glow if it
is zero or positive (a few volts) the tube will glow. The transistors
are then not required to handle much voltage or current as 2n414 was
a low power alloy junction germainium (Vce of -20V and Pd of 150mW) so
it could not switch much current or voltage. Any display used had to
be operatble with less than 20V (more like 15or less) and only a few
milliamps.
I've also seen several such racks and displays down in RI. Basically
the system is built of standard logic elements available in the late
50s early 60s and an element could be a gate or Flip flop and likely
not many gates and only one FF to a card. Voltages were typically low
in the less than 15V range. The cards rarely were a complete
computer but more like a sequencer or other fixed logic system that was
designed for a specific use.
Use care powering that as power supplies may have bad caps, and wires
may be cut/shorted.
Allison