DEC Precision CRT Display Type 30 Reproduction

[MICHAEL GARDI]

When Oscar Vermeulen released his PiDP-8/I reproduction I knew that I had to have one. When I got mine assembled I thought it would be cool to connect to it through a "period-ish" terminal so I created a 2:3 Scale VT100 Reproduction. Now Obsolescence Guaranteed has released their new PiDP-1 Replica. While I wait for mine I thought I would make a 2:3 scale DEC Precision CRT Display Type 30 Reproduction to go with it.

I started a project blog over on Hackaday to record my progress. So far I've just outlined my design thoughts there but I have started putting together a prototype. 

I could use a little help. If anyone in this Group has access to a Type 30 a few photos with rulers placed in the foreground would go a long way producing and more accurate reproduction. The numerous photos available online fall a little short because they lack scale and because of parallax introduced distortions.

Thanks

Mike  

[Matheus Ferro Costa]

Why 2/3 ? Make it a full fledged full size

I was investigating rewirings in regular crts to behave like a vector display. Some crts could fit inside the case, unfortunately not a green one. Monochrome crts in theory don't have shafow masks but recoating one don't seem easy

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[Bryce Jeannotte]

I like the direction you are going with this. What were you thinking of using for the filter? Acrylic or something else? 

[MICHAEL GARDI]

Thanks Bryce. I was thinking something like this might work: https://a.co/d/7y5EqFP

Mike

[MICHAEL GARDI]

Well my main reason for going 2:3 is that I believe the PiDP-1 is 2:3 scale as well. Just trying to be consistent. A CRT would be nice but I don’t have budget or the EE skills to pull it off. I also hope to make a Type 30 reproduction that would be relatively easy for others to copy. (I will make and Instructable when I am done with all my plans and design files.)

Mike

[Glenn Babecki]

Michael,

Much like yourself, I was thinking of creating a standalone Type 30 display replica rather than embed the flat panel display in the PiDP-1 speaker panel.  Your Hackaday project prompted me to search for either original equipment dimensions or images to obtain scale information.  I couldn't find any mechanical engineering drawings, like an Illustrated Parts Breakdown (IPB) document and I haven't come across a related document number to pursue the search further.  I suspect such documents are out in the "wild" but haven't been scanned and placed in any online archives.

I'm sure you've scoured the Internet in search of revealing pictures of the Type 30 display, but I came across one that has some potentially useful artifacts for scaling.

https://www.computerhistory.org/pdp-1/929c912b55dbaf61f368648268c713e7/

This picture is interesting on two counts:  first, the photo is a fairly head-on view of the display thus minimizing the parallax distortion and second, there are collections of fan-fold paper tape on the display desk in various orientations.  Given that the fan-fold paper tape section is 11 inches long, it appears to be the next best thing to a ruler; just short an inch. 😉  There is one paper tape that is laying horizontal on the desk which also minimizes the parallax relative to the display face.  I haven't done the exercise but I bet the paper tape would provide a pretty good scale to get some better measurements of the overall display front.  Using the paper tape to measure the supposed 16 inch CRT surface should either confirm or deny the viability of this approach.

Additionally, I could swear that I came across another Type 30 recreation project, but I'll be darned if I can find it again.  I seem to recall the designer also used a small-ish TFT LCD display (presumably with an HDMI interface) and constructed an enclosure out of plastic, fiberboard, or some similar material.  I could probably find a 10 inch LCD display which would be roughly the desired 2:3 scale for the PiDP family.  I was thinking it might also be possible to repurpose an older, slightly larger (13 inch?) laptop LCD display, assuming I could find a suitable LCD controller.  However, this might be more work than just finding a roughly 10 inch display.

Just a few thoughts.

Regards,

Glenn

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[Matthias Barthel]

I found this screen at AliExpress:

https://a.aliexpress.com/_Eyz1Yno

It works fine with my raspberry, i take a test as a second screen on the raspi to display the crt output on the round display.

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[MICHAEL GARDI]

Hey Glenn,

Yes I did a lot of searching and I ended up with a picture similar to the one you found except yours is better as it is more "head-on". I brought the image into Fusion 360 and calibrated it using the 16" circular opening for the CRT which I assumed is correct. With the calibrated photo as a background I traced out the hex case walls and created the following model. 

I don't have a good side image yet so I just did the "face" for now. Even at 2:3 scale the case is 16" x 14" with about a 10" opening. If I do the sides I might not have any room to to put the reproduction. I'm in the process of printing the case, screen mask, and a frame to hold the 10" 4:3 aspect ratio LCD panel I found. It will go together like this:

I don't think a round screen is required for this project because the "active" area of the original Type 30 is a 9.5" square which is only about 6" scaled. The 10" panel I am using is only half an inch shy of this so a pretty close fit. I am hoping that placing a translucent black or green plastic sheet between the display and the screen mask will hide that fact that there is a rectangular screen behind the round cutout.

Mike

[Whit Turner]

Instead of Aliexpress, just look at the Waveshare 5" model here - it is widely available: https://www.waveshare.com/5inch-1080x1080-lcd.htm

Not exactly 2/3 scale but it would be a good alternative.

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[Glenn Babecki]

Mike,

I'm glad the photo worked out for the scaling.  I've come across a lot of repeat images too, but that particular one jumped out at me for the combination of usable features in the scene. 👍

I definitely agree a round screen isn't required for the reasons you cited.  It's great that a roughly 10" display accommodates the scaled 6" aperture.

The sides of the Type 30 case are tapered towards the rear of the display, but clearly a desktop reproduction doesn't have to be that deep.  The taper to the case is pretty slick (kind of in a Star Trek sort of fashion), but the space would be wasted on the lack of innards to the display elements.  In fact if you make a "flat panel" version as your design appear to be, then there wouldn't really be much for the side of the display housing anyway.

I use Onshape and as I recall there isn't a good way of importing a fully parametric model from Fusion360.  Perhaps when you work out the layout you could share at least an export of your design.  The preferred Onshape import format is Parasolid B-rep (.x_t or .x_b) from v10.0 to v37.0.  However, SOLIDWORKS (.sldprt) 1999 to 2025 and Inventor 9 up to 2026 are good alternatives.

My PiDP-1 order fulfillment caught me off guard and is supposedly arriving tomorrow!  I've got a bunch of things to clear off my plate before I can start construction so it's going to be a busy fall.

Nice work on the display this far, so crack on!

Glenn

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[Oscar Vermeulen]

This is exciting! I wanted to do this too, but did not get around to it. My idea was to make the sides of the case from white PCB panels, soldered together. I added the Kicad project (unfinished) in case anyone wants to take that idea further.

Kicad project attached, for whoever wants to do whatever with this.A 7" HDMI should fit inside, just about, explaining why the front is slightly wider than tall. The HDMI comes out of the side, which is why I got depressed about the idea :-)

 

[Bryce Jeannotte]

Mike, 

I printed a 2/3 scale VT-100 and it was about 4" deep. I found this to work very well. I did add some fishing weights (I am not sure if they are lead any more) to the bottom of the display and the unit is quite stable. 

Bryce.