>So is that what you're going to do for us, alank2? :)
Absolutely. One lamp with hopefully the original driver or something similar to see what it does!
I also found this:
Which shows a circuit, but isn't the same as the PDP-8/I, though it may give a hint.
I emailed the guy with good front panel pics to see if he could tell us the components used.
The rise time is 30.5 milliseconds and the fall time is 68.5 milliseconds.
I'll have to try measuring some of the LED's on the PiDP-8 tomorrow or when I get a chance.
FWIW, the 8/L used bulbs, transistor drivers (base fed from TTL), +10v, and the pull-downs from bulb to GND were 1K 1/4w 5% CC. When not running, the bulbs were discernible (you could tell that the machine was on from a few yards away – even if you could ignore the fan noise!), although inter-bulb brightness variation was quite noticeable with all in the nominal off-state – with some bulbs appearing to be fully “off” and others merely dim to a varying degree.
We actively programmed from the front panel so a bad-bulb was a real problem. I cut my baby-teeth (this was in 1972) on that machine with bulb replacement …
Response time on TTL-high was hardly an issue; improving bulb life most definitely was. It was non-trivial to extract the front panel, and then carefully desolder bulbs. Never lost a pad that I can recall, but I’m sure that I lifted a few :-<.
Had much fun adding home-brew external 28Kw static memory (2102-arrays) + controller to that basic 4Kw core machine. Since the 8/L is essentially a no-frills 8/I it was possible to directly leverage the 8/I design documentation, which I certainly did (and was very thankful for having it!). In retrospect I’m rather amazed that it worked out so well; it was the first time I ever took a soldering iron to a computer …
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