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Thread: Repro SCELBI interfaced with Popular Electronics Scopewriter and ASCII keyboard

  1. Default Repro SCELBI interfaced with Popular Electronics Scopewriter and ASCII keyboard

    This is something that was done back in the day and I felt that I had to recreate this combination of devices. I also have a little 256 byte monitor hacked together. The monitor supports reading and writing memory and executing programs through normal keyboard input. These add ons turn the SCELBI 8H into a machine that approaches practical usefulness. More details can be found on my blog.

    http://www.willegal.net/blog/

    Regards,
    Mike Willegal

  2. #2
    Join Date
    Jun 2014
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    Thanks for this Mike. it inspires me to build my scelbi soon.

    Len
    Spread the joy of Vintage Addiction

    -->www.chronworks.com/<--->www.i8008.net/<--

  3. #3
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    Oct 2017
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    Very nice, nothing like an analog X-Y display. Too bad analog scopes are getting older and AFAIK aren't being made anymore. That output on a digital scope looks bad (I've tried).

    I've build a Spacewar display for my PiDP8 and used a (fairly rare cheap) Tek 604 display in great shape for it. It's far better in resolution and linearity than my in rather good shape 464 (which is a relative of your 465). Being a few inches larger helps. I have a few Tek 620's with dubious aging tubes and/or bad switching transistors, but the working ones were noticeably better than the 464.

    You always read about projects involving converting a CRT TV to an XY display, but few have actually done it (and lived, apparently). And then, I wonder about the frequency response and linearity.

  4. Default

    The Scopewriter is not, strictly speaking, an X-Y display, as it only draws in the X axis. This makes it a vastly simpler solution than some others, at the cost of supporting only one line of output.

    The SCELBI CRT interface does draw characters in an X-Y fashion. It is interesting in that it does this with two OP-AMP integrator circuits, one for X, one for Y. The main problem I have with my Tek465 in this application is that the Z input is capacitor coupled and reacts a bit slower than would be optimal for the SCELBI CRT interface. The thing I like about the Tek 465, is that when something goes wrong, it seems to be quite repairable, and as it is 40 years old, I do have an occasional issue with it. I agree that many other scopes have better display resolution.

    regards,
    Mike Willegal

    Quote Originally Posted by Slob View Post
    Very nice, nothing like an analog X-Y display. Too bad analog scopes are getting older and AFAIK aren't being made anymore. That output on a digital scope looks bad (I've tried).

    I've build a Spacewar display for my PiDP8 and used a (fairly rare cheap) Tek 604 display in great shape for it. It's far better in resolution and linearity than my in rather good shape 464 (which is a relative of your 465). Being a few inches larger helps. I have a few Tek 620's with dubious aging tubes and/or bad switching transistors, but the working ones were noticeably better than the 464.

    You always read about projects involving converting a CRT TV to an XY display, but few have actually done it (and lived, apparently). And then, I wonder about the frequency response and linearity.

  5. #5
    Join Date
    Oct 2017
    Location
    Kentucky USA
    Posts
    24

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    I bought a broken 464 as a parts source for my good one. Then I repaired it. Diode bridges, of all things. These were among the last TEK oscilloscopes without (for the most part) unobtanium semiconductors.

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