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View Full Version : Got my SWTPC TVT II TV Typewriter today!



falter
December 16th, 2013, 04:07 PM
My TVT II arrived today. Wow. This thing is neat. Easily the oldest computing item I have right now. And slightly different than the other TVT II's I've seen online. One of the ICs is white ceramic, there are a couple of empty spaces on that same PCB where others have a couple of chips, and the keyboard appears to be a slightly different model than what was commonly used. Still amazing to have something like this in my possession of years of reading about 'build it yourself PCs'. Now if only a real Don Lancaster TVT would show up. But I have a feeling that would be a LOT more money. :) I don't know if I dare power it up. There are no broken wires or anything. However what I assume is the video feed wire has a little earphone-style connector on it. Not sure exactly how it interfaces with a TV or monitor? (or did old monitors have that sort of jack instead of/in addition to an RCA jack?

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falter
December 16th, 2013, 04:08 PM
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Chuck(G)
December 16th, 2013, 04:20 PM
The board with the blank spaces is the serial board, with a UART--if memory serves, it's the GI (AY-xxxx) equivalent of a TR1602. Unlike the UARTs that you're used to, this one requires a 16x clock to be jumpered in. Without the extra ICs, ISTR that you can get 2400 bps only. Adding the extra components, which include the rather uncommon SN7497 rate multiplier, you can get several other frequencies.

There was no jack supplied with the kit--you supplied your own. It's composite BW video; nothing special.

The 6 chips on the memory board should be 2102 (1kx8 ) RAM. They run very hot. They were supplied with the kit stuck into foam and wrapped with aluminum foil.

The TVT was comparatively easy to build, compared to the MITS 8800.

falter
December 16th, 2013, 04:51 PM
The board with the blank spaces is the serial board, with a UART--if memory serves, it's the GI (AY-xxxx) equivalent of a TR1602. Unlike the UARTs that you're used to, this one requires a 16x clock to be jHaven't foundd in. Without the extra ICs, ISTR that you can get 2400 bps only. Adding the extra components, which include the rather uncommon SN7497 rate multiplier, you can get several other frequencies.

There was no jack supplied with the kit--you supplied your own. It's composite BW video; nothing special.

The 6 chips on the memory board should be 2102 (1kx8 ) RAM. They run very hot. They were supplied with the kit stuck into foam and wrapped with aluminum foil.

The TVT was comparatively easy to build, compared to the MITS 8800.

Thanks! So I could probably just purchase an adapter then. I'd like to get one of those small 70s monochrome monitors for it and my Apple II.. saw one in a picture with a TVT II that displayed a cool blue color.

I'm still not clear on the exact relationship between SWTPC and Don Lancaster.. I know the TVT II was a different design.. but we're the original TV typewriter boards also made by SWTPC? Or did people completely fab their own? Havent found a clear answer yet.

Chuck(G)
December 16th, 2013, 05:24 PM
Don Lancaster (still around; check tinaja.com) authored a number of hobbyist-grade DIY books. The TVT was described in detail in a Radio Electronics article, and simultaneously offered for sale as a kit, by SWTP. Mine was the original CT1024, built from a kit in 1975.

I used a 60's portable Zenith TV (tubes in it, not transistors) and just tapped into the video section. Problem was that it was a hot-chassis model, so you had to be careful how you plugged it in. I used it for quite a while.

A couple of modifications I (and others) made to our kits was to change the 2 pages of 512 (16x32) characters to 1 page of 16x64. Another change was to decode received data and create control sequences to clear the screen and move the cursor. I actually got WordStar 0.9 to run on the thing. The supplied keyboard was awful. I took an old RCA Spectra 70 EBCDIC keyboard and reworked it to supply ASCII. It was a beaut--used sealed reed George Risk keyswitches.

For $275, the SWTP kit (you could buy complete kits or just the bare PCBs0, was a pretty good deal.

falter
December 16th, 2013, 05:31 PM
Don Lancaster (still around; check tinaja.com) authored a number of hobbyist-grade DIY books. The TVT was described in detail in a Radio Electronics article, and simultaneously offered for sale as a kit, by SWTP. Mine was the original CT1024, built from a kit in 1975.

I used a 60's portable Zenith TV (tubes in it, not transistors) and just tapped into the video section. Problem was that it was a hot-chassis model, so you had to be careful how you plugged it in. I used it for quite a while.

A couple of modifications I (and others) made to our kits was to change the 2 pages of 512 (16x32) characters to 1 page of 16x64. Another change was to decode received data and create control sequences to clear the screen and move the cursor. I actually got WordStar 0.9 to run on the thing. The supplied keyboard was awful. I took an old RCA Spectra 70 EBCDIC keyboard and reworked it to supply ASCII. It was a beaut--used sealed reed George Risk keyswitches.

For $275, the SWTP kit (you could buy complete kits or just the bare PCBs0, was a pretty good deal.

Cool! Did you keep yours? I was reading through one of the articles and they had these PCB 'templates'.. I'm assuming there's a way to create your own PCBs from those if you wanted to? Or am I misunderstanding what those were for?

Chuck(G)
December 16th, 2013, 05:52 PM
No, I gave a some of the remaining parts away a few years ago. Compared to regular professional terminals, the TVT was pretty awful. I picked up another single-board terminal a couple of years later that had 24x80 display. I may still have the serial card from mine, I don't know.

No, you could make your own PCBs from their plains. Those who elected not to do it that way, just wire-wrapped up a board.

falter
December 21st, 2013, 06:24 PM
I adapted the connector on the end and tried plugging into my Apple iii monitor. But what I get is distorted video that is basically like a tv with the vertical hold not set properly. I can at times briefly make out a solid block.. 20x20 characters or so of ? Marks. Chuck to your recollection were these units designed to be hooked up to a standard monitor, or are they supposed to go thru an RF modulator to a tv?

Chuck(G)
December 21st, 2013, 07:00 PM
I used a standard (TV) monitor with mine--no modulator. Have you checked the documentation?

It might be a DC level issue--try coupling the video through, say, an 0.1 uF ceramic cap.

falter
December 22nd, 2013, 12:20 PM
I used a standard (TV) monitor with mine--no modulator. Have you checked the documentation?

It might be a DC level issue--try coupling the video through, say, an 0.1 uF ceramic cap.

Yes.. I made some adjustments to the trimmer resistors and was able to see the garbage it was displaying a bit more clearly.. but I cannot get it to give me a nice solid background. Has a giant black spot in the middle if run off my Commodore 1701.

Here's a video. I think I've got a whole bunch of issues. It's gratifying to see some text.. not really sure where to begin looking to get the screen itself into proper alignment so that I can start figuring out which circuits/chips aren't working.

You can kind of see in the video it occasionally will blurt out a line. It's not very legible in the video but it appears to be some kind of machine language statement. Comes and goes. The rest is just those vertical characters, or the occasional flash of all ? marks.

http://www.youtube.com/watch?v=1a3QUAikGp4

Chuck(G)
December 22nd, 2013, 01:52 PM
Looks like a hum bar to me. Perhaps your PSU filter capacitor has dried out? That would hardly be surprising.

platis
December 22nd, 2013, 04:49 PM
Very nice item! Hope you work out the issues! Do I understand things correct when I say it's no cpu/mcu in tv typewriter? It's all done with TTL/CMOS logic?

Chuck(G)
December 22nd, 2013, 06:12 PM
Very nice item! Hope you work out the issues! Do I understand things correct when I say it's no cpu/mcu in tv typewriter? It's all done with TTL/CMOS logic?

Exactly so. Not the first instance of this by any means--and no CMOS. Just some MOS (PMOS) devices.

MikeS
December 22nd, 2013, 07:00 PM
Exactly so. Not the first instance of this by any means.Fer sure; I've got the remnants of a CDC terminal that pretty well fills a substantial desk; no CPUs, (E)(P)ROMs, LSI etc. at all. Lots of diodes though... ;-)

@ OP: Lancaster published several books about TVTs:

TV Typewriter Cookbook,
The Cheap Video Cookbook,
and
Son of Cheap Video (includes "You can now add a complete video display system to your KIM-1 ... for a total cost of $7 and using only five cheapie integrated circuits."

Don't know if they're on line anywhere but might even be worth buying if you're interested in TVTs.

platis
December 23rd, 2013, 02:28 PM
I looked though the " TV Typewriter cookbook" today! Very interesting I must say! A good history lesson and for me a bridge between old teletype stuff and more modern computer terminals(vt52, vt100), great! You also get a glimse of semicoductors of the day and their pros and cons, it happened a lot in the seventies! It also very interesting what you can do without microcontrollers, today you use such for everything!

Chuck(G)
December 23rd, 2013, 04:44 PM
It's pretty amazing what can be done with a PROM and a latch. Finite state machine (http://cs.smith.edu/dftwiki/images/4/49/ROMBasedSequencer.pdf)

The floppy controller in the Apple II is little more than that--a shift register, PROM and some random logic.