The sound is provided by a tape deck situated inside the dome (which also contains the circuitry for the timer and lights). The design seems to vary from ride to ride. Some (presumably earlier) models have cut down reel-to-reel tape decks while others have eight track cassette players fitted. It is more than likely that many of these have since been replaced by more modern alternatives.
The circuitry housed in the dome became very hot and this seems to have caused a number domes to become brittle, crack and shatter - leaving a hole in the top, exposing the electrics. This hole was often hidden by the creative addition of a flashing beacon. It is possible that later models had a beacon fitted as standard.
The soundtracks also varied. Some have sound effects taken from the Dalek movies, while others play the Doctor Who TV theme and/or produce a ranting Dalek voice. What the 'factory standard' tape was is unknown.
The original colour scheme is consistently red (pigmented fibreglass gel coat). However, may hours in the sunshine often bleached the colour to a mild pink, at which point the rides were often repainted in any of a multitude of colour schemes.
In collecting terms, these rides aren't for the feint-hearted. The cast metal frame/base that carries the motor takes two men to lift. The main carcase is 'all in one' from below the neck, down to and including the fender. The floor is reinforced, and the carcase is thickly laid up in fibreglass.
The basic GRP hemispheres are integral to the skirt but are then enhanced with spun aluminium covers (in two different sizes). Many of these covers have succumbed to small prying fingers as they are only held on with contact adhesive, which would have become soft under the warm summer sun. The slats are thick aluminium, but still managed to become snapped on some units.
Exactly how many of these rides were made is a matter of debate, though it is believed that they numbered between 35 and 50, manufactured in the UK somewhere between 1964 and 1967.