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Thread: Why was Sinclair selling UK model ZX81s in the USA?

  1. #1

    Default Why was Sinclair selling UK model ZX81s in the USA?

    When you look on U.S. eBay there's usually about a 50/50 mix of U.S. and UK Sinclair ZX81s for sale (from North American sellers). Maybe some of the UK models were personally brought over by British expats, but that can't possibly be the case for all of them, especially since many of the UK models are bundled together with a U.S. power supply, U.S. RAM expansion module ("ZX81 USA" printed on the back), and U.S. literature. That was the case with my ZX81 that I got on eBay a few years ago -- the computer itself is a UK model but everything else is from the USA, as shown in this video.

    Just a little clarification: in addition to being rebranded and sold by Timex in the USA as the Timex-Sinclair 1000, the ZX81 was also sold via mail order from Sinclair Research in Nashua, NH. The U.S. model is distinguished from the UK model by having a channel 2/3 switch underneath for its RF modulator, whose output jack is towards the rear of the case, while the UK model's RF output is closer to the other jacks. The U.S. model also has the New Line button marked as Enter and the Rubout button marked as Delete. And on the bottom it has "ZX81 USA" printed on it, with an FCC ID.

    Now here's the smoking gun: a UK model ZX81, in the original box, with the original shipping label, showing it being shipped from Sinclair Research in New Hampshire to a U.S. customer:
    https://www.ebay.com/itm/112994034031

    So the question is, does anybody know why Sinclair was selling UK ZX81s in the USA? The closest thing I've come up with is a letter I saw of Sinclair explaining to a U.S. customer who had bought a ZX81 kit that they had run out of kits and had instead shipped them a fully assembled machine at no extra charge. So is it also possible that during this time of peak demand for ZX81s, Sinclair was also selling UK models to U.S. customers as a substitution?

    Back in the day of manually tuned TVs, it was no big deal to use a UK ZX81 with a U.S. TV set, because the UK channel 36 (which virtually all British computers use) matches up with U.S. UHF channel 34, and with an adjustment of the V-Hold knob, you can get an old TV to sync up to the 50 Hz refresh rate instead of the 60 Hz used by U.S. TV signals. (In this case the difference in color subcarrier frequency between PAL and NTSC is irrelevant because the ZX81 is of course black & white.)

    So that's my theory of what was going on -- but I'd love to hear from anyone who either has proof of it, or an alternate explanation. Did anyone here in the USA or Canada order a ZX81 from Sinclair Research back in the day and get a UK model? Or know anyone else who did?
    Last edited by vwestlife; May 18th, 2018 at 02:25 PM.

  2. #2
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    American Express was selling them through the card statement* before Timex made the agreement to sell them and Timex sold ZX81s for about 6 months before finally getting the TS 1000 ready. Of course, by then, the system was no longer competitive and local schools got flooded with unsold stock.

    * Wikipedia states the rate of total US sales as 15 thousand a month in January 1982.
    Last edited by krebizfan; May 16th, 2018 at 05:15 PM.

  3. #3
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    The TS-1000 was not a rebranded ZX-81. It was a different machine with an NTSC ULA, 2k of RAM, a U.S. power supploy and the other differences you pointed out. I worked for Zebra Systems who sold them and supported them with add-on items.

    Do you think current owners would want reproductions of the old Zebra add-ons like the joystick adapter and keyboard beeper? Or, possibly even a Votrax SC-01 Voice Synthesizer board?
    -----[ Al ]-----

    3 - TRS-80 Model I, TRS-80 Model 4D, LNW-80 Model I, Coco, 3 - Coco 2, Coco 3, 2 - Tano Dragon 64, C64, C64c, C128, 2 - Atari 800XL,
    Atari 520-ST, Atari Mega-2 ST, Amiga 1000, TS-1000, TS-2068, ZX-Spectrum, IBM 5150, 2 - Apple ][gs, Laser 128, and a butt load of Macs and Intel PCs.

  4. #4

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    For those of you that want to use a RAM expansion on one of these, I can tell you about some magic stuff. As a demonstration as to how well it worked, I'd have it running code and take the unit and drop it to the table from about 1.5 feet. I recall that before the magic stuff, if I accidentally bumped it, even while sitting on the table it would crash the program.
    Anyway, you need to get some DC-4 from an electrical shop ( or McMaster-Carr ). You put a little on the connector pins.
    Dwight

  5. #5

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    Quote Originally Posted by Al Hartman View Post
    The TS-1000 was not a rebranded ZX-81. It was a different machine with an NTSC ULA, 2k of RAM, a U.S. power supploy and the other differences you pointed out. I worked for Zebra Systems who sold them and supported them with add-on items.

    Do you think current owners would want reproductions of the old Zebra add-ons like the joystick adapter and keyboard beeper? Or, possibly even a Votrax SC-01 Voice Synthesizer board?
    joystick adapter, yes

  6. #6

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    Quote Originally Posted by Al Hartman View Post
    The TS-1000 was not a rebranded ZX-81. It was a different machine with an NTSC ULA, 2k of RAM, a U.S. power supploy and the other differences you pointed out.
    Interesting. Are there any compatibility issues between the two?

  7. #7

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    Quote Originally Posted by Al Hartman View Post
    The TS-1000 was not a rebranded ZX-81. It was a different machine with an NTSC ULA, 2k of RAM, a U.S. power supploy and the other differences you pointed out. I worked for Zebra Systems who sold them and supported them with add-on items.
    Wouldn't the U.S. model ZX81 have the NTSC ULA as well? I know the TS1000 has 2K of RAM instead of 1K, but I thought that was the only real difference between it and a U.S. ZX81.

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    There was only one ULA which handled both NTSC and PAL. The difference between the two is a resistor attached to a specific pin on the ULA to force 60 Hz video operation and a different modulator.

    http://blog.tynemouthsoftware.co.uk/...video-mod.html shows how add a switch to change the TS1000 from NTSC to PAL.

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