A brochure on the brimistor, early 1960s
The brimistor was brought into the circuit of the Vox AC50 in late 1965 (certainly by 28th November) and is principally found in amps built at the Burndept works in Erith. See the overview on this page. Its purpose was to retard the main supply voltage for a short time to allow the heaters of the valves to warm up.
The Brimar Factory at Footscray, where the brimistors were made, was only a short distance from Erith.
The type of brimistor chosen was the CZ4. "CZ" indicated that wires for soldering on were provided. Brimistors were also sold in "fuse" format, with no wires.
The voltage / current curve of the C4 / CZ4 is given on this page.
The images will enlarge if clicked on.