Acorn
Teletext
Adapter
Here we can see the inside of the Acorn Teletext Adapter. The four red wheels at the back are connected to variable resistors which set the frequency of the four television stations.
It is an issue six board and from the date codes on the chips, it must have been made in mid to late 1984.
The board and metal plate at the front of the unit are the Adapter's power transformer. The board is marked as being made by St Ives Windings.
In addition to the 0v, +5v and +12v commonly found on BBC computer related equipment, there is also a lead going to a connector marked +40v.
The two largish chips mounted in holders running down the middle of the Adapter are an SAA5020 and an SAA5030. I am not sure of the exact function of these devices but they must be some form of teletext decoders similar to the SAA5050 found inside all BBC micros.
The Teletext Adapter apparently has 1K of memory for buffering a page of teletext but I am not sure where the memory chip or chips are to be found.