It would help to mention the series starts in 5 April 2002 issue 4166 and the electronics appears in 2003 Feb issue 4188 page 156.

It is built on vero board and the article says "no knowledge of electronics is required." then fails to explain what it is trying to do and even involves an oscilloscope in the testing. Poor presentation.
Get the parts from Maplins.

So what is it doing. In effect it is like windscreen wiper control. If you flick the switch you want the wipers to go on and do a full run not stop half way across the screen. This circuit is to make it do one rotation of the ball lifting archemedian screw so it has a start switch, a keep going circuit, and a stop switch. Armed with this knowledge you can go to a 15yr old schoolkid and have them make one usig a 555 timer chip as their GCSE project. They do that stuff at school these days but they will probably want to use a microprocessor.

Why not do it without electronics? The sparking on switch contacts and high starting current for little motors is bad for switches life expectancy. This system uses low current in the switch and might get 1 million cycles out of it.

It's simple enough, I think the original arrangement may have been over-complicated. What is needed is a mechanical brush and track arrangement on the screw so that if the motor is started the brush makes contact and the screw turns one revolution until it returns to a (small) gap in the track. The ball itself is used to short out two rails and provide power to the motor long enough for the brush to turn past the gap.

I think the reason for the electronics was that the ball didn't make contact reliably or for long enough for the brush to leave the gap, with the obvious consequence that no replacement ball would be driven from the top of the screw.

As has been said, the web is awash with simple, reliable 555 timer circuits*.

Also, might it not be better to power this device from the mains, transform it down to 12v, to save having the hassle and expense of those big batteries? But what do I know.

As long as you don't fear the return of the 3-day week and power rationing

Neil

*These days you could replace the 555 with a microcontroller at less cost. In fact the microcontroller could replace the entire clock and be more accurate, but I don't think that's the point… hence my personal preference would be for a totally electromechanical solution.

The "Painting by Numbers" approach to the electronics part of these articles was, I think, unfortunate.

However; the circuit is very simple and the devices used are robust.

If anyone is interested in following the circuit, rather than just assembling it; here are some recent NXP DataSheets for the chips.

HEF4528B

HEF4011B

Hope that helps

MichaelG.