In late 1964 everything changed. The Beatles went on tour in the USA with a full complement of AC80/100s; Jennings Musical Industries won an order for a substantial amount of equipment from The Thomas Organ Co., based in Sepulveda, California.
From "Beat Instrumental" magazine no. 18, October 1964. The "Million Dollar" contract, signed at the British Music Trade Fair in late August while the Beatles were touring.
It was probably not long after the signing of this deal that Vox made plans to move production of the AC80/100 from Westrex in West London, to the Burndept factory at Erith, where AC30s were already in production.
Above, the facility on West Street, Erith owned by Burndept Electronics and shared with Vox.
Westrex, which made the AC80/100 throughout 1964, was evidently not geared up for volume manufacturing.
However, the Burndept factory seems to have taken some time to get going. AC80/100s only started rolling off its line in appreciable numbers in March 1965.
Piece on Tom Jennings from "Beat Instrumental no. 19, November 1964.
"We first supplied The Beatles with Vox equipment three years ago and we are still doing so. When they went to America for the first time they did a show at the famous Hollywood Bowl and found that their 50 watt amps just couldn't pierce the screams of the audience, so, they asked us to produce something even more powerful. The results are their present 100 watt monsters."
"The Beatles' tours of the States created a terrific demand for our equipment and led to our contract with the Thomas Organ Company to supply them with five million dollars worth each year."
In relation to The Beatles in the USA, Jennings presumably meant 50 watt amps at the Washington Coliseum, not the Hollywood Bowl. "Five million dollars worth each year" probably encompasses a degree of hyperbole.
But strange to say, in early 1965 there was a definite "famine" of AC80/100s. Very few bands are seen with them. There was certainly a promotional set of amps on hand at the BBC (British Broadcasting Co.) for use on "Top of the Pops" and similar shows, but apparently very little in the shops, or available for export
Above the Kinks playing on "Top of the Pops" in November 1964. The same set of amps was also used by the Yardbirds in December.
At the NME Pollwinner's concert in April 1965, only Paul McCartney had an AC80/100 (his first amp, reboxed). Everyone else used AC50s.
The earliest dateable pictures to have come to light so far of US bands with AC80/100s are those of the Byrds and Paul Revere and the Raiders at the CBS promotional show in July of that year.
The Byrds live on stage at a CBS Sales Conference on 5th July 1965, shortly after "Tambourine Man" went to number one in the U.S. All three guitarists are plugged in. The AC100s must, at this date, be cathode biased (AC80/100s). This is the earliest dateable picture that has come to light so far of an American band using, on stage in the USA, AC100 SDLs that did not belong to the Beatles or any other English band.
For a pic of the Raiders on that day see this VoxShowroom page (though the amps are not AC100 Mark 2s as implied there). At a concert in Phoenix in 1965, date unknown, the Byrds had just the AC50 and two Foundation cabs - see this page.