Sinclair kits

From: Scott Ware <>
Date: Wed Sep 3 10:31:23 1997

(Sorry for the message on a dead thread - i've been catching up on an
e-mail backlog.)

I ordered two of the ZX81 kits from Zebra Systems in January - one to
relive the ZX81 building experience (with a better soldering iron than I
had 15 years ago), and one to keep around in kit form. I received the
kits about 2 weeks after I placed the order.

The ZX81 kits from Zebra are early (issue 1) releases of the ZX81, and
include a UHF RF modulator. Video format is selectable between NTSC, PAL,
and SECAM by changing a few resistors. There are different connections
for the RF modulator marked marked USA, UK, and Fr on the board; however,
the assembly instructions say to ignore these and connect the modulator to
the UK and Fr connections. The RF output is approximately on UHF channel
33 in the US. In the Sinclair minimal cost tradition, the RF modulator is
not crystal controlled and the output frequency tends to drift - a
television tuner with adjustable fine tuning is a good thing to have.
Alternately, you can pick off composite video before the RF modulator and
use it to drive a monitor. Although the ZX81's video output is not
particularly well suited for driving a 75 or 300 Ohm load, the picture is
usable, and the addition of a single-transistor amplifier stage for
impedance matching can provide reasonable composite video output.

The supplied power supply has a 110 VAC input and outputs 9 VDC at 1A, so
finding a replacement power supply for your local AC line voltage
shouldn't be much of a problem.

Zebra (or the tech school that Zebra bought the kits from) supplies their
own instructions, which are geared towards assemblers in the US. The
Sinclair instructions are not included. Assemblers in countries that use
non-NTSC video standards will need to look at the schematic to determine
the correct positions of a few resistors. Fortunately, the schematic
diagram is included. The two books that are included with the kit ("BASIC
Basics" and "Basic Basics of Basic BASIC", or something like that) aren't
(in my opinion) useful for much other than pointing out some of the
peculiarities of Sinclair BASIC.

ZX81 kits were available in the USA by mail order ($149 kit, $199
assembled, IIRC) for about a year before Timex started selling assembled
T/S 1000 machines here. Some other Sinclair-branded machines were sold in
the US as well; I have US-spec ZX80, ZX81, and QL machines. The
machines (that I know of) that were sold by Timex are as follows:

Timex/Sinclair 1000 - 2K RAM version of the ZX81

Timex/Sinclair 1500 - 16K RAM version of the ZX81 in a rubber-key
Spectrum case

Timex/Sinclair 2068 - Enhanced 48K Spectrum with 3-voice sound, extended
video modes, some weird bank switching logic, a cartridge port, and a
joystick interface. Plastic keys and a space bar. Some of Timex's
improvements supposedly made their way into the 128K Spectrum.

There was also supposedly a Timex/Sinclair 2048 (not the same as the
Timex Computer 2048), which, I assume, was a 2068 with less memory or
fewer features.

Scott Ware            
Received on Wed Sep 03 1997 - 10:31:23 BST

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