At one point in the '70s - '80s at least some of the Reading steel MUs were given a very interesting speedometer - a small black metal box with two large blue plasma numerals in it. Highly interesting to see this very small but very high-tech for its time device in what appeared to be an otherwise-unmodified engineer's position.

Does anyone here have details of the history of this system or its components? Has any of the equipment survived?

remember that led displays were already in hand held calculators and Nixie Tubes even before then especially on early computers.

I am a great fan of older display technologies.

These are notable for being actual blue-green gas plasma numbers, and were also notable for being fairly large (over 2" high, as I recall, but never measured them) now-familiar seven-segment numbers. (I am particularly fond of the blue plasma displays as they were used on my favorite Olivetti ET200-series typewriters in the early '80s)

They were installed in a very small surface-mounted box where they could easily, and clearly, be seen. I meant to look underneath and see what they used for sender/encoders, but never did (and always thought I could go back and check when I had the time). I never saw that particular technology used on any other locomotive or car, and of course the world changed to LCDs and then dot-addressable color computer screens quickly thereafter.

I wondered how long the displays would last as it had to be in a bit of rough environment, heat/cold, shock. Any of the cars preserved?

That's what I'm trying to find out ... if any of the surviving cars still have the gas-plasma display, or better yet the whole system, still installed.

These gas plasma displays were actually heavy-walled vacuum tubes with fused grids inside, and were very durable and tolerant of low and high temperature. Even if the caps in the circuitry have gone bad, the 'expensive' part of the system would not likely be damaged. GM and Ford used this technology for many of their 'electronic dashboards' in the '80s and I find when these "fail" it's because of the HV supply to the tubes making them go dim, not because the displays themselves are bad, or the actual display logic and addressing to them is bad.

Now, this was just two digits in a box (no need for two-and-a-half, let alone three, on a Reading MU in the services it would be running by then!) and I remember them flickering a bit so the drive may have been multiplexed like contemporary LED segment displays.

Note: this was NOT the red 'hockey puck' as seen here:


After all these years, this was still one of the coolest pieces of elegant design 'in context' I can remember.

[If it helps, this was on one of the official "retirement" trips for the green Reading MU fleet, a trip to Doylestown in the mid-Seventies (as I recall, after the famous use of GG1-hauled MUs during the strike then)