Four pin XLR mains socket - Amphenol 91-859. Three pin XLR speaker socket - Amphenol 91-855.
Amphenol connectors replaced Cannon hardware at some point mid-production of the "100W Amplifier", i.e. the fixed bias AC100 without the brimistor. Power sockets were 4-pin and marked with a red dot (which seems to have been exclusively done for Vox - presumably Thomas Organ helped in the US). The earliest amp that has so far come to light with a circular Amphenol XLR on its back panel is serial no. 531.
XLR mains connector - Amphenol 91-858 - latching, blue and white.
XLR speaker connector - Amphenol 91-854.
Above, Amphenol brochures advertising "Qwik" connectors - used by Vox for AC50s and AC100s from mid 1965. The Allied Industries pricelist gives the cost in dollars for various bulk orders. It seems likely that JMI acquired these connectors via the Amphenol factory in Whitstable (Thanet Way, Kent, CT5 3JF), which had been set up in 1961. Whitstable is an hour's drive away from Dartford along the Kent coast.
"Flight International" magazine, July 1964. Advertisement for Amphenol - the new factory at Whitstable, on the Kent Coast, around 40 miles from the Vox Works at Erith.
Amphenol connectors were first adopted by Vox in mid 1965. Up to that point Cannons had been used.
It may be that Amphenols were suggested by Thomas Organ, which was in mid '65 in the process of setting up its own line of amplifiers - the solid state "Super Beatle" (fitted with Amphenol speaker connectors) - and so on.
Well to note too that Burndept Electronics, with whom Vox shared the Erith Works, had long been involved in avionics - notably in the mid 60s the Midas flight recorder, which raised doubts from the first.
The Observer, 22nd November, 1964. Prophetic words.