A communications scrambler, converting messages into A-line pulse codes. The converter on Fosforon was constantly manned by three technicians. The TP crystal, essential to its functioning, was located within a high voltage area: Avon referred to 250,000 volts flowing through the circuitry. Avon sabotaged the converter so that Tynus could draw a spare crystal from the stores, allowing Avon to take the original. The sabotage effects could be attributed to a fire started by Tynus. Avon ultimately destroyed the converter after removing the crystal, hoping its absence would not be missed.