2 colour television with 2 CRTs

Forum for discussion of electronic television. Generally, stuff to do with CRTs and not using mechanical displays.

2 colour television with 2 CRTs

Postby aussie_bloke » Sat Feb 15, 2020 11:00 pm

It's been a long while since I posted here. In the past few months I have been working on building a two CRT two colour television system and have successfully got it working and thought I'd share it with you all. This project is not exactly NBTV but the two colour principle is loosely related to Baird's later experiment with colour television with his Telechrome 2 colour tube system and more so related to a RCA two colour system developed alongside their triniscope 3 colour system in the late 40s. My system is a modern equivalent of the RCA two colour system and using same colours which are orange-red and blue-green.

RCA.jpg
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I originally was going to use two oscilloscope tubes but thought it was more feasible to use two near identical small B&W TVs with identical tubes as they're already working TVs and I only just need to input the two video signals to each. Fortunately I do indeed have two small B&W TV sets from the early 2000s with identical tubes and so I scrapped the plastic bodies, mounted the tubes onto custom made mounts and positioned them at 90 degrees to each other. I placed yellow and red gel filters over one set and blue and green filters over the other. I put a semi transparent mirror (piece of glass with window tint) between the tubes positioned at 45 degrees. I mounted the system onto a big wooden board.

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I initially thought I could simply output RGB from a DVD player just using R and G to the composite video inputs of the two TVs but found it was not as easy as that. The DVD player's outputs are Y, Pr, Pb and only Y has a sync pulse. I was able to still test the system using two DVD players with two DVDs of still images in orange-red on ond DVD and blue-green on the other DVD and the system did display them successfully. At first I was getting a mirror image of the reflected CRT (the blue green CRT) and so I thought "dahhhh Troy you need to reverse the picture" so I reversed the horizontal coil leads and and that fixed that issue.

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So I had to build a colour matrix board that will take YPrPb and output each as primary colour video with sync and so I looked at Richard Diehl's triniscope colour project http://www.labguysworld.com/TinyTriniscope_001.htm and build the matrix board he designed http://www.labguysworld.com/YUV2RGB_Matrix.htm but with a slight modification which is to place a trimpot at the outputs of green and blue to mix them and adjust the mixing of the two colours.

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So I built the circuit and it initially had a number of problems mostly caused by a chip that was the right number but wrong brand which there were differences in minimum voltage. After putting the right chip in and getting the matrix board operational it I was successful in getting the two colour TV system to work. I had to then get the mirror and CRTs aligned as best as possible so I adjusted the height and size of the scan on both sets to get a close match as well as positioning the translucent mirror and securing it with blutack. I also adjusted the brightness/contrast controls on both TVs to get the best looking two colour picture and also adjusting the trimpot on the matrix board to get the best looking mix of green and blue. I ended up with a lovely looking two colour picture on the two colour TV and am pleased with it!

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2ctv overview.avi
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Now that it's working I need to neaten things up. Firstly I will need to make this system run off one power source as I'm using two 12V power jacks for the 2 TVs and a +-5V power supply for the matrix circuit, this is really cumbersome so will need to make a power supply that will supply 12V 1A to both TVs and 1 AC lead going to that and the transformer feeding the +-5V supply. Then I will need to get a proper half mirror and properly fasten it rather than use trusty blutack. And then make a cabinet around the system.

Anyways I've made video logs of my construction of this 2 colour TV system which can be viewed on my YouTube channel in my playlist here https://www.youtube.com/watch?v=dGQdmsc ... oM6Trdr4Tl and also here is a video recording of the 2 colour set in operation displaying some clips from a Countdown episode https://www.youtube.com/watch?v=hmQep3VzbYk .
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Re: 2 colour television with 2 CRTs

Postby Steve Anderson » Sun Feb 16, 2020 2:41 pm

Some time ago (years) I knocked up a RGB-YUV matrix...

viewtopic.php?f=10&t=1541&hilit=RGB&start=15

With some juggling around it could be reversed to provide YUV-RGB, or with suitable tweaks Y, Cb, Cr or Y, Pb Pr to RGB.

Nothing amiss with Labguys version, just this is somewhat simpler, though arguably not as good. Looking back at my version now, I would make some minor changes...

Although my discrete RGB-YUV version used 5v TTL inputs it's OK with analogue inputs, the gains would need some adjustment though. I'd also replace the three Darlington output stages with something like MPSA13/14s and remove R219, R234 & R244...that saves six components. The BF199s could be replaced quite happily by BC548s or 2N2222s...easier to get a hold of...

Steve A.

Looking through the drawings related to this I did change the output Darlingtons to MPSA14s and adjusted the gains for 3v3 inputs. There is no reason that it couldn't handle standard analogue inputs levels around 1v with some tweaks.

It would still need some clamping arrangement, an LM1881 sync-extractor, unless the source is DC-coupled (unlikely).
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Re: 2 colour television with 2 CRTs

Postby M3DVQ » Sun Feb 16, 2020 11:34 pm

This is a bit late, but doesn't the player give RGB on the SCART output?
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Re: 2 colour television with 2 CRTs

Postby Steve Anderson » Mon Feb 17, 2020 4:49 pm

Some players do, some don't. Also instead of RGB it can also be a colour-difference signal, YUV and the like. Plus most players outside Europe don't have a SCART connector, only the RCA/Phono outputs.

As per audio and the DIN connector, only for Europe generally, thankfully (I hope) long gone...

I do have a DVD player here with a SCART connector, (a Pioneer imported from Hong Kong) the pins allocated for RGB/YUV aren't connected to anything internally...I have looked...

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