Cabinets, part 2a
AC100 cabinets - 4 x 12s with Midax Horns
The Beatles in San Francisco, 19th August 1964 - the first date on the US late summer tour.
The large AC100 cabinets - the ones we perhaps associate most with the Beatles - were designed and constructed (initially) for John Lennon and George Harrison in August 1964 to replace the large box AC50 cabinets that the two Beatles had used with their new AC80/100 amps in Stockholm on 28th July.
The Beatles in Stockholm, 28th July 1964. See also page 3.
As Jim Elyea has made clear (J. Elyea, Vox Amplifiers. The JMI Years, p. 447, 588-589), the basic form of the new cabs seems to have been arrived at largely thanks to Henry Glass, the driving force behind "GlaRev", the company that made cabinets for Vox. Effectively they were to be the size of two AC30 cabinets stacked one on top of the other. But since Goodmans Midax mid-range horns were envisaged too, the format in reality, was more akin to two small-box AC50s on top of each other, with increased depth so as not to require cut-outs for the horns in the back panels.
Above, the Beatles with their small-box AC50s at the Washington Coliseum, February 1964. One can see the circular cut-out for the horn in the back of John's cab. The design process was something of an ad hoc business. Take a standard AC30 cab, modify its appearance, alter the backboard, and make a cut-out for the horn both front (ie. on the baffle) AND back. Without the hole at back, the AC30 cab was not deep enough for the Midax.
Celestion T530 speakers ("Celestion blues") were rated at 15 watts apiece. The semi-closed backboard probably brought their overall handling up to 35-40 watts - not really enough for an AC50. The horn, rated at 25 watts, gave the cab further protection - 60 watts handling in total. With its upper mid-range frequency "lift", the Midax was clearly to the benefit of an amp that could produce a considerable amount of bass. AC50 amplifiers sold by Vox for bass had exactly the same circuitry as those sold for guitar. See the Vox AC50 website for further info.
Below, shots of two Midax horns. Further info is given on this page.
On the left, the older of the two, still with its screw terminals in place (as used in AC100 cabs). In the middle and on the right, a later example with solder lugs. Both have a "flat" finish. Still later models have a textured coating.
AC100 cabinet and speakers
The new cabinet, constructed out of good baltic plywood, as all early Vox cabs were, was 40 inches high, 27 1/2 inches wide, and 11 1/2 inches deep, allowing plenty of room for the horns; and it sat in a handsome chrome-plated swivel trolley, as in the pictures below. Castors were furniture castors made by Shepherd, still available today.
Left and far right, a Mark 1 - so-called simply for convenience (never termed in this way by Vox) - trolley and cabinet discovered in Denver by Mitch Colby. Note the rectangular "basket" on top. Centre left, an advert for the AC100 Super Deluxe from early 1965. Centre right, Lennon larking around with a cabinet and trolley.
The basic construction and layout can probably best be judged from the hulks of later cabinets that appear from time to time on ebay.
On the left and in the centre, the remains of an American Super Beatle cab. In terms of layout, Super Beatle cabs followed their model, the AC100, though this one (being a late example), has a particle board (chip board) baffle. On the right, an earlier Super Beatle cab, with a birch ply baffle, and hooded castors on its swivel trolley.
Almost as if to reflect the solution arrived at for the format (two small-box AC50 boxes one atop the other), the cabinet was divided by interior shelf, separating the two sets of speakers and horns from each another. The speakers chosen by Denney were the new 8 ohm Celestion 1088 alnicos, painted silver, and with doping around the edge of the cone to allow a greater power handling, 20-25W each probably being their maximum. Where the AC80/100 was concerned, this was certainly enough.
Pictures of early T1088s in an AC30 cabinet. Note that the terminals are still on the struts of the frame. In early to mid '66, the terminals were moved to a small board between the struts. For more on the T1088, see this page.
The internal wiring of the new cabs was the now familar series/parallel arrangement, but one must not forget that all this was still very new in 1964; and the presence of horns (and the capacitors needed to protect them from the full power of the amp, especially the low frequencies) necessarily added extra complexity. But the Vox solution as usual was surpassingly elegant.
Pictures from Jim Elyea's book. On the left, the terminal block and capacitors in his Mark 1 cabinet. Note the use of two core mains cable! The capacitors are large GPO style 4uf affairs (two in parallel to give the required 2uf). On the right, the wiring system laid out diagramatically. In contrast to later wiring schemes, the Midax horns have their own mini-circuit - by far the best way of arranging things - but labour-intensive in production terms.
The Beatles received their new 4 x 12 cabs at the Futurist Theatre in Scarborough, on the north east coast of England. The picture on the left below records the event (repeated from this page).
Denney drove up from Kent with his wife Dolly, and Alan Harding, one of the Vox engineers. The cabs travelled separately in a van, probably with a new thin-edged AC80/100 for Paul McCartney. Speaking of the trolleys, Dave Petersen says (Dave Petersen and Dick Denney, The Vox Story, 1993, pp. 54-55):
"These were first fitted to The Beatles' AC100s prior to their 1965 (sic) U.S. tour, and on a pre-tour "warm-up" concert Scarborough, where the stage had a slight forward slope, it only took the opening number to start a general forward movement of the bass cabinets. This could have gathered quite some momentum by the time it reached the front of the stage, but fortunately Denney, who was usually along at Beatles' concerts, was able to take a grasp of the trolley and spent the next two numbers kneeling behind the cabinet until some blocks were found. Braking castors were fitted from then on."
Note however, that Paul's trolley already had brakes (pictures below), and that to judge from later pictures, AC80/100 and AC100 trolleys never to have had them. But the intention, nonetheless, may have been present in Denney's mind after the Scarborough concert. In the US tour of August and September 1964, the need for brakes was obviated by the removal or loss of the castors themselves.
The Beatles and Mal Evans backstage at Scarborough with Cherry Rowland in 1964. In the first two pics Paul's trolley and AC80/100 is visible on the right, already with brakes. John's foot is probably on another AC80/100 in cover, beside which sits a large box AC50? Pictures from the Mirrorpix photo archive. Right, a repro trolley, illustr. J. Elyea, Vox Amplifiers, p. 306.
The Beatles used their cabs and basket-topped trolleys through to April 1965. By the time we see the band on tour again in Summer 1965, they have a new set with parallel bars on the trolley tops.
2nd November 1964, Queen's Hall, Belfast. One can still see the rectangular "basket" for the amp on George's trolley.
One of the many wonderful pictures taken at the Palais des Sports, Paris, 20th June 1965. Parallel bars for the trolleys.
Quite how many of these early basket-topped trolleys and Mark 1 cabs were made and sold is difficult to say. But they were certainly provided by Vox for major bands and events:
Gene Vincent and The Londoners on stage at the Empire Pool, Wembley, 20th November 1964. The eagle-eyed will have noted that the AC100 (actually AC80/100) on the trolley is in a thick-edged box without corner protectors. A further AC80/100 in a thin-edged box sits on the drum riser.
Above, the Kinks on the BBC also in December 1964. This set of amps was also used by the Yardbirds (with Eric Clapton).
For other pictures from 1964, see this page. As far as surviving units go, however, Mitch Colby's may be the only one - a rare bird indeed.
Later changes (1965 - 1967)
As has been mentioned, a new style of trolley and cabinet was released in 1965 - called for the sake of convenience, the Mark 2. The trolley had parallel bars on top instead of the squared-off basket, and the cabinet had a simplified mode of wiring. These, one suspects, were measures to help reduce production costs and to make production itself easier. For a selection of surviving cabs - click here
Above, the original cab of serial no. 392, produced in April 1965. Note the capacitors now next to the horns.
Click for a larger downloadable image
The wiring schematic. Also available with notes on this page.
Further pages will cover the use of AC100s by the Beatles and other bands from 1965 - 1970, including of all people, The Beach Boys (below). Note that the cabs are swung almost parallel to the floor in the trolleys.