Indicator tubes for transistor logic machines.

Date: Sun, 28 Oct 2007 14:03:43 -0400 From: Bob Shannon <bshannon at tiac.net> Reply-To: "General Discussion: On-Topic and Off-Topic Posts" <cctalk at classiccmp.org> To: "General Discussion: On-Topic and Off-Topic Posts" <cctalk at classiccmp.org> Subject: Indicator tubes for transistor logic machines. 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.