UPDATES: August - December
The identity, or rather "type", of the Goodmans speaker used in certain Vox SDL cabs in 1966 is now known: it was the 241H/1214/15, a driver apparently originally developed for Selmer. Images of the cabs are gathered on this page.
Earlier versions had five hexagonal bolts on top and a slightly different label, with cutouts in the relevant places:
Below, the light version of the same driver - the 241/1214/15 - note the smaller magnet. The number on the paper label on the rubber ring around the magnet is probably the stock part (either 03560 or 63560).
The Stones playing Cleveland Public Auditorium, 3rd November, 1964. Photos by George Shuba. Bill has his AC80/100 and two Foundation Bass cabs. The one behind Keith has Bill's AC50 on top, as spare, in its black (?) cover, no logo.
Small inset picture added below of a diamond-input AC50 with a maroon cover.
26th December (2)
Further info and notes on amp and speaker covers in 1964 to accompany/augment the posts below:
Sylvie Vartan with The Beatles, photo session at the Olympia Theatre, Paris, January 1964. Note the covers of the backup AC30 cab and amp - brown for the former, red/maroon for the latter.
Covers for an AC80/100 and 2 x 15" cab; a mark 1 AC50 and Foundation Bass cab; and a set of LS40 PA columns survive in the same brown.
Old pics, though still useful, of red/maroon covers for a reverb unit and AC30 head. Maroon was also used for some AC50 and T60 heads and LS40 PA cols.
In re. AC100 SDLs, no cover seems to have been provided for the 4 x 12" cab - only for the amp section.
If one sees an AC100 cab with a cover it is likely either to be from a Super Beatle, fitting snugly to the cab itself, and with slits down the sides to allow the pivot wheel to protrude through; or it is from a Supreme, fitting over the trolley, but with a late logo - the letters "VOX" surrounded by an ovoid in white.
Illustrative pics to follow.
The baggage car sequence from "A Hard Day's Night" - shot in mid March 1964. Covers for the AC50 amp and cab, probably black given their intensity.
Above, Cherry Rowlands with The Beatles backstage at Scarborough, 9th August 1964. Click for a larger image. At John Lennon's foot, one of the early AC50s in its cover (no logo). Picture from Alamy.
Added below, pictures of the AC30 to which the red cover with cursive VOX logo belongs.
Revisiting Vox covers with cursive logos:
Paul's first AC80/100 in Abbey Road studios - note the logo on its cover. Detail from a picture, probably taken prior to or during the "Baby's in Black" session, published in Beatles Book monthly.
An AC30 cover in red. The amp has brown grille cloth, charcoal tolex and a copper control panel.
Correction: this is not a Foundation Bass cab cover, but a single speaker AC10 cover. The AC10 was probably from early 1964, thin-edged box, brown grille cloth, serial number in the mid 4000s,
To date no examples of AC50 covers with such logos have come to light (though that is not to say none exist) - only plain green and brown so far.
Serial number 1034
A diamond input AC50 mark 1 from the second quarter of 1964.
It has been known for some time that an AC100 belonging to, or at least used by, The Beatles survives in Florida - possibly one of the ones used in the UK winter tour, 1965. The owner: likely still to be Barry Gibb of the Bee Gees.
Above, a grab from the page of Billboard Magazine in which the details are disclosed. Click as ever for a larger image. The page can be viewed on Google Books
The piece, by Chuck Taylor, is entitled "The Bee Gees. Four Decades of Success" in Billboard Magazine, issue for March 24th, 2001.
THE BEE GEES, 35 YEARS OF MUSIC
[QUESTION] "You also got something else from the Beatles that is used on the title track and first single from your new album, "This is Where I Came In".
MAURICE: (Smiling, nodding) "That's right. The guitar I play on the track - but not on the video - of "This is Where I Came In" is an acoustic Gibson Monarch. Years ago, what I got for my 21st birthday was a movie camera from Ringo [Starr] and a guitar from George [Harrison] and a Monarch guitar from John [Lennon]".
"The one from George is the 12-string Rickenbacker, the  Shea Stadium [concert] one, which he also used on recordings."
"What also happened was, when the Beatles stopped touring in the 1960s, we ended up with their equipment: the Vox amps and the microphones and stuff like that they used when they toured round Britain!"
"Barry ended up with John's Vox amps, and Vince Melouney ended up with George's amps. I had the bass speaker with the bass amp on top that was Paul's. So we had all this stuff, and it all went away gradually. But we stil have the Vox amp that Barry had that was John's."
20th December (2)
A better picture of Los Brincos c. 1965 with their three AC100s. The trolley of the bass cab is effectively two halves of an SDL trolley cut down.
The Who at the Richmond Jazz Festival, 6th August 1965. Pete Townsend has four AC100 SDLs daisy-chained, and John Entwistle has two AC100 amps driving four 2x15" cabs. Photos from left of stage show that there are another two AC100 SDLs behind Pete's four, presumably "just in case". See the page on the wonderful ukrockfestivals site.
Note the covers on the two AC100s at back of stage. They're slipped on only so far as the lower corner protectors. Surviving AC100 covers fit extremely closely - one has to lever them gently over the protectors on the lower corners of the amp cabinet.
Flyer from the festival.
For pics of The Who on stage in Copenhagen, September 1965, with six AC100s - two each for Pete and John, and two spares - see further down this page.
Serial number 249, early 1965, recently sold on ebay. The amp is now registered here.
Serial no. 859 still exists in excellent condition. Thanks to Robert for the info. Pics on this page.
Two letters from the appendix of the Thomas Organ Vox service manual of 1967. The first indicates that some AC100s (actually AC80/100s) at least had found their way to the States by early December 1964. See the entry for the 30th May, below.
An American Super Beatle trolley, in many respects similar to UK-made AC100 trolleys. However, the castors have "hoods", and an open-work circle surrounds the swivel fixing points instead of a closed one, as below:
12th November (2)
A cab that sold on ebay in 2014. In need of some attention but structurally sound, and with its original trolley. No speakers are present however. The rectangular Cannon XLR connector suggests mid 1965 in terms of date.
A cab that appeared on ebay earlier this year. In spite of the US Super Beatle trolley, it is certainly English - note the backboards and the Cannon XLR connector. The original grille cloth has probably been replaced with Thomas Organ cloth. No scrim is visible behind it.
At least one Midax horn survives. The speakers, which are later replacements, are Vox-branded Celestion lightweight ceramics - G12S - probably from a PA speaker column from 1966. The presence of the rectangular Cannon XLR indicates that the cab is earlier - pre mid 1965, when round Amphenols came in.
Serial number 796 (an AC100 Mk 2 from the last quarter of 1965) now known to exist (in Italy). Thanks to Tommaso for the info. Pics to follow.
An early solid state rectified (non-brimistor) AC50 that popped up on ebay in the summer of 2016, baffle and back board absent. Probably from late summer 1965. Chassis number 934. Pot codes "GM" = June 1965.
Two things of particular note - the preamp valves branded VOX and with Thomas Organ part numbers, and the presence of a Werth Surgistor (a sort of brimistor surrogate) under the lip of the preamp by the voltage selector - bottom right hand picture of the four above, far right.
The amp was clearly serviced at some point in the later 1960s at a Thomas Organ Vox service centre and fitted with a surgistor-brimistor in accordance with the latest AC50 schematic.
The same seller (in Kansas) also had an AC100 "100W Amplifier" (early fixed bias, no brimistor), produced in the late summer of 1965. That amp had a Werth Surgistor fitted later too. It may be that the AC50 and AC100 were purchased at the same time and serviced at the same time a few years later.
That both amps were produced for export is clear from the presence of a grey 0.01uf 500v Radiospares "snubber" capacitor (not represented on the schematics) at their mains switches (positioned to the left of the choke in the AC50). The same capacitor (again not on the schematic) is also found on T60 amps designated for export to the USA.
This entry has also been posted on the AC50 site.
AC100 serial number in the low 500s, currently in the UK. The amp came with a Thomas Organ service parts list, and set of schematics, one unrecorded elsewhere. For further pics of the amp, see this page, and for the late hitherto unique schematic, see here.
Three old ones (one in a US trolley)
Below, pictures of Gene Vincent on stage with "The Londoners" at the Empire Pool, Wembley, 20th November 1964. Note: the thick-edged AC80/100 (no corner protectors) and SDL cab, the thin-edged AC80/100 on the drum riser, the early AC50 large-box trolley with a "basket-top" rather than parallel bars, and the Rickenbacker 325 belonging to the guitarist far right(a thing known for some time to Rickenbacker afficiandos).
Click for a larger image
A tantalising pic found through Google Images, scooped up from somewhere on ebay at some time. Grille cloth on both amp and cab looks old (rather than reissue), and the cab has the right sort of logo for its potential date (wooden block with letters individually fastened). But without further pics, the set could simply be a well-made repro.
Pictures of a set of five matched RCA-branded Mullard XF2s posted here. These were the sort of valves that could be purchased in the USA to serve as replacements when the original EL34s that were supplied with AC80/100s and AC100s gave out.
1st October (4)
An early Foundation Bass cab in smooth grey tolex registered here.
1st October (3)
Charlie Watts on stage at the Hara Arena, Daytona, Nov. 13th 1964. Beside him Bill's AC80/100. Note the controls, all set to 1 o'clock. Picture from the Daytona daily news site.
The rear of the amp, with its two speaker outputs side by side, is seen in pics from the Long Beach concert (below) on 1st Nov. 1964. A set of pics from the concert here.
1st October (2)
AC100 serial no. 1994 currently on Reverb with two cabs
From the early days of ebay, a single pic of a Foundation Bass cab cover with cursive Vox logo - probably from 1964. Not many of these around.
Mullard BY100 rectifier diodes, used in AC100s from 1964-1967, in their original packet.
Two cathode bias amps side by side - late Westrex on the left, late Burndept on the right.
Advertised on marktplaats.nl a little while ago, a late AC100 and a cab from the first half of 1966. Note the square corners to the backboards on the amp (a serial number therefore in the high 1900s), and the Amphenol speaker connector on the cab - the Celestions though still have terminals on the struts, rather than in between.
The Who in Copenhagen, 25th September 1965, with six AC100s (two spares on the drum riser). These were the new fixed bias "100W Amplifiers" - one can tell by the two screws on the top edge of the backboard. Cathode biased amps had only one.
Entry from thewhothismonth site: - "The 10th (October 1965) finds The Who at Stockholm airport in Sweden to begin their two-day tour. Unfortunately, their equipment has been flown to Gothenburg for their second stop so the band is forced to borrow instruments from their opening acts The Moonjacks and The Mascots for their show at Johanneshovs Isstadion in Stockholm [at least one AC100]. The next night they rejoin their equipment to play two shows at the Cirkus Lorensbergs".
A quick update on the 2x15". There are of course no date codes on early 15" Celestions as the gasket is felt.
Cone code is 32 751/002. Note that 39 751/002 and 40 751/002 have been reported on late 60s/early 70s units - on this page of an excellent thread on Celestions of all sorts.
The cab measures 12" deep, 19" wide (the same width as a thin-edged AC80/100), and stands 36" high. The outer edges of the speakers sit tight up against the handle recesses. Eight screws on the baffle hold the Celestions in - washer, nut, grip washer, then a second nut. The impedance of each is 16ohms, the pair wired in parallel for a total of 8ohms.
A nice brown-front 2x15" cab from late 1964, blue Celestion 1074s having given way to silver ("poly grey") T1108s and T1109s. Date codes of the speakers will be posted in the coming days.
Note that the grille cloth of AC80/100s, with which these cabs were conventionally paired, changed from brown to black at around serial number 230, in late 1964. The bass cabs page has now been updated.
A new picture page added on a late Westrex-made AC80/100.
The well-known aerial shot of the Beatles on stage at the Isstadion, Stockholm, 27th July 1964, John and George with their new AC80/100s and special AC50 cabs. One of the early AC50 amps is present on the drum-riser as back-up.
Page on Foundation Bass cabs tidied and updated.
Pictures from the Stones' second US tour, winter 1964, the first from Long Beach (1st Nov. 1964), the second from an unknown venue. Note Bill Wyman's amp - cathode biased, two Cannon XLR outputs low down on the back panel. Also note that his cab has carrying insets in the sides - the earliest datable instance so far of this new style. Earlier Foundation Bass cabs had flat sides - see this page for examples.
More from KRLA Beat Magazine - 24th July 1965 - the publicity picture taken in 1964 of the Stones with what was probably Bill Wyman's first thin-edged AC80/100. The KRLA magazine archive is online here.
Denis Payton of the Dave Clark Five on stage at the Carousel Theater, West Covina, California, 27th June 1966 - photo published in the 23rd July issue of KRLA mag. In the background an AC100 and one of the band's new 7120 cabs. This is the first dateable instance of a non-Beatles 7120 cab.
Pictures taken a few months later show that the band had four. Given that the DC5 summer tour began in early June 1966, it seems likely that the cabs were delivered to them in late May.
Royal Variety Performance, winter 1966. The four 7120 cabs and trolleys together on stage with four AC100s
Picture of Keith Relf of the Yardbirds with an AC100 to his left published in KRLA Beat Magazine, 5th Feb. 1966
The Yardbirds, Paris 30th May, 1967, with three AC100s.
A detail from a pic. of the Stones playing at Wigan, November 25th, 1963. Note on the left the early Vox LS40 speaker with its unusual fixing for the chrome stand. Normally one would see a round handwheel.
Most pages now updated. AC80/100 serial number 236 (black panel) and what is likely to be its original cab and trolley pictured here. The cab unfortunately lacks its original horns and speakers; the amp's electronics have been redone by a tech.