The Vox AC50 Mark 2
Valve rectified, grey panel, twin channel, small and large box versions, 1964-1965
500-600 produced - JMI schematic OS/053
An early Mark 2 chassis - serial number 1411, with original link voltage selector. As indicated by the slider board, this chassis was sold in a large box.
Roy Orbison with "The Candymen" on stage at the high school gym in Eau Claire, Wisconsin: November 11, 1964. Note the AC50 and Foundation Bass cab at right.
Vox "Precision in Sound" newspaper format catalogue, late 1964. The first illustration of the new large box AC50 mark 2, though the blurb wrongly says that the amplifier has only two inputs. The amplifier section of the AC50 Super Twin (for guitar) represented in the catalogue is still in a small box.
The idea behind the AC50 Mark 2 was simple - to improve the tonal range of the amp: the "Normal" channel to serve both bass and guitar, and the new "Brilliant" channel solely for guitar.
The schematic (circuit diagram) is OS/053 - see this page. The AC50 is designated the "AC50/2", indicating in this case, the two channels delineated.
From late 1964 to early 1965 around 500-600 valve rectified AC50s were produced. One often finds higher estimates, but those generally neglect to take into account the fact that Vox gave its 50 watt Public Address amplifiers serial numbers in the same sequence. In early 1965, the new Mark 3, solid state rectified AC50, was introduced.
The design process was a relatively quick one. The general arrangement of the chassis - the disposition of the transformers, tag-boards, capacitors, and so on - was simply taken over from the AC50 mark 1.
Indeed, AC50 mark 2 chassis fit perfectly, albeit tightly, in small boxes designed for AC50 mark 1s. Around sixty grey panel twin channel AC50 Mark 2s were issued in this way in late 1964:
Serial number 1436. The AC50 mark 2 chassis in these small boxes could just as well have gone into a larger box - one chassis fits both.
Further examples can be found on this page.
The new AC50 speaker cabinet for guitar
The size of the new speaker cabinet for guitar had been worked out by the end of July 1964: the Beatles had two for their shows in Stockholm, but fitted with 2 x 15" speakers to cope with the power of the Vox AC80/100 amplifiers issued to John and George shortly before. Detailed photographs are available on the Vox AC100 website.
The Beatles, Isstadion, Stockholm, 27th July 1964. The amps are Vox AC80/100s, the cabs, large-box AC50 format but with 2 x 15" drivers.
The size of the speaker cabinets as devised for the AC50 mark 2, is noted in the advert below, from August 1964:
"A.C.50 SUPER-TWIN. A new 50 watt model with built in 'glass shattering' treble and full, deep tone bass. Speaker cabinet houses two 12" loudspeakers and one special metal top frequency horn. Dimensions 33" x 23" x 11 1/2". Amplifier section: four inputs, separate volume and tone controls, dimensions - 19" x 11" x 7 1/2"."
The AC50 amplifier described and pictured is apparently still the diamond input, Mark 1. Although Vox adverts and illustrations can often be a little out of step with production, it does seem as though the new AC50 speaker cabinets came out a short while in advance of the revised AC50 amplifier.
Below, Tony Hicks of the Hollies in Studio 2, Abbey Road, July or August 1964, with a cab and amp set very similar to the one outlined in the advert above:
Recording session for the album "In the Hollies Style", released in November '64. The number of diamonds on the grille cloth shows this is a large box AC50 speaker cabinet. Whether the amplifier box contained an AC50 Mark 1 (diamond input) amp, or a new twin channel AC50 mark 2 is unknown.
Manufacture of the AC50 Mark 2 amplifier
Early AC50 mark 2s were assembled by Triumph Electronics, 118-122 Brighton Road, Purley, under contract for Vox/JMI. On Triumph see this page.
For most of late 1964, finished chassis were transported in batches to 119 Dartford Road for final assembly ("making up"). Chassis were provided with wooden boxes, and the speaker and mains wires inside the amplifier soldered to the connectors on the back board. Back boards had the serial number plates attached.
Before the amp was sent out, serial numbers were noted in a ledger, along with details of the recipient (agent, shop, or person). These ledgers unfortunately perished in the 1990s.
In 1965, chassis will have been sent to the Vox / Burndept Electronics Works at Erith. The despatch department was on the top floor.
The main drive in late 1964 was to supply amps to the USA - to fulfil the requirements of the "Million Dollar" deal forged with Thomas Organ. A good number of the new AC50 mark 2s are likely have gone straight to the States.
The sense comes across from the surviving amps that JMI stockpiled several weeks' worth of output from Triumph to form sensibly large transatlantic shipments.
American adverts for the AC50 can be found towards the foot of this page. Below, a Thomas Organ service bulletin from December '64:
Below, some pictures of the 4th Teen Age Fair, California, April 1965. These are the earliest to show American bands with imported AC50s (rather than AC50s brought to the States by English bands):
The Bay Area leg of The Battle of the Bands, March 1965, Santa Ana - a prelude to the final in April. At left, a small box AC50 with new large speaker cabinet.
Above, The Challengers, a surf band, playing during an interlude in the competition, 16th April, 1965. Note on stage, the large box AC50 and AC80/100, plugged into their speaker cabinets (out of picture to the left), but not being used.
For more on the competition see this page on the Vox AC100 website.