When Mark enters the control cabinet there is a row of giant light bulbs shown along the back wall. These were not specially built props, but real bulbs of a type often used for studio set-lighting.
The alien device is actually the same prop used as the reactor in the Seaview. The various pipes and fittings are also the same.
The last episode of the series.
This is Production number 4723. It was the 23rd episode to be produced of the second season, but the 25th and last to be broadcast.