Re: [PiDP-11] Inconsistant LED color

[Bert Driehuis]

Can't speak about your batch of course, but the LEDs of mine match the color of my memories of the PDP8/e of yore (the PDP11/23 I maintained later was of the boring panelless generation, so the LED's aren't as burned into my psyche as the PDP8 was).

Capturing LEDs is always difficult. Maybe try an old fashioned digital camera? Or see if your phone app has a pro mode in which you can influence the exposure?

Cheers,

Bert

On Wed, 8 Oct 2025 at 22:29, Phillip Porch, MD <ppp...@gmail.com> wrote:

I noticed when testing the LEDs that some were a pretty bright white while others were less bright to my eye and had a yellowish color. Did anyone else see this? It looks OK kind of like some of the incandescent  lights of old were not exactly the same. I tried to take a picture but They all appear white. Maybe if I take it with a strong light, the LEDs wont be so blown out on the photograph.

This isn't really a problem as far as I am concerned but an observation. It is like there were 2 lots of LEDs with different whites one being slightly yellow.

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[Phillip Porch, MD]

Bert, I too grew up on a PDP8/e when I was in college. I’ll try and use a pro app to post a photo. I have been offered more LEDs but I’m fine with what I have. It brings back memories. I can almost remember the program I had to key in with switches. I think it was the rim loader to load in the bin loader from paper tape. Ahhhh the old days. 

[terri-...@glaver.org]

Oddly, I don't see the original post that was quoted here. Anyway...

The red of my PiDP-11s seems accurate. I'll have to bring one of mine on a trip to the LSSM and check against the 11/70s there.

I never saw the actual lamps of a KA10 front panel (I was dialing in from a TIP hundreds of miles away. My PiDP-10 kit has LEDs from 2 different batches (confirmed by Oscar/CEDS) intermixed. I haven't decided if I want to do a wholesale replacement or not. I'm leaning toward not, as the actual KA10s had their lamps changed over time as the originals burned out. There's also a KA10 with red LEDs in its front panel. This was apparently done "back in the day" as management got tired of having to take the system down to replace burned-out lamps.