The Brimistor (Brimar Resistor)
14-10-65 Brimistor added.
Above, serial no. 6023 - the brimistor can be seen at the front of the chassis on two standoffs to the right of the mains transformer. For further pictures, see this page.
Serial no. 4282 - no brimistor - and no holes for the standoffs or the feed-through for the underchassis wiring. Pot codes for this amp are "GM" = July 1965. For further pictures see this page.
The Brimistor was added by Vox to solid state rectified AC50s (and AC100s) as a means of delaying the inrush current when the amp was first switched on - an attempt to mimick the "slow start" provided by the GZ34 valve rectifier - the idea being that the heaters of the output valves had time to warm up before the rest of the circuit rose to operating levels.
Implentation evidently ran from around the date registered on the schematic until the end of JMI.
Whether the brimistor really worked as intended is a moot point - but the idea at any rate was a good one.