VOX AC100 - UPDATES AND NEW INFO
December 2018
30th December (3)
The new index page for the JMI documents:
Click to go to the index page. Captioned links are given to the items that have been posted so far.
30th December (2)
The documents from 1961 and 1962 are now being assembled on pages of their own:
Introduction and amplifier pricelists here.
Guitars and hire purchase details here.
Illustrated catalogues and coloured flyers to follow.
30th December
1962 - the pricelist following the phasing out of the AC30/4. The AC30/6 (AC30 Twin) is now 115 guineas. See the first entry for 29th Dec., below.
29th December (2)
Below, a TCC (Telegraph Condenser Company) folder of technical bulletins from 1962, just arrived. Green TCC micromite electrolytics were used in AC100s from early 1965 through to 1966.
Again, values are given both for "Peak Working Volts" and "Surge Volts".
A 32uf 350v TCC micromite in AC80/100 no. 392.
29th December
One of the documents encompassed in a batch sent out in November 1961 in response to an enquiry - see the Jennings form letter below, 16th December.
Various new things are in train: the add-on tone circuit; the AC10 and AC15 twin; the AC30 super twin; and the discontinuation of the AC30/4.
The pricelist corresponding to the announcement. Note that the AC30 (six input) twin is 100 guineas.
28th December
Some more screengrabs from the BBC documentary on Screaming Lord Sutch and the Savages, filmed in late 1964, produced and aired in 1965. Shots of Ricky Fenson, the group's bassist, putting the AC80/100 in the Commer van after a gig.
27th December
Some notes on Paul McCartney's 2x15" brown-fronted speaker cabinet, used through to the end of the USA autumn tour, 1964:
A detail of amp and speaker cabinet, Washington Coliseum, 11th February, 1964. In the sliver below, one can just see the BASS flag of the cab.
Just visible, the BA of the BASS runner.
Amp and cab on stage, New York, Carnegie Hall, 12th February, 1964.
Adelaide, 12th June, 1964. The cab's BASS runner has gone.
Las Vegas, 20th August, 1964, detail of the speaker cabinet with Paul's second brown-fronted amp.
Not Las Vegas, but Forest Hills, 28th August.
Above, Toronto, Maple Leaf Gardens, 7th September, '64. At some point before the autumn tour of the States, the cab evidently had a new connector fitted - a rectangular Cannon. The original circular Cannon can be seen below, backstage at Versailles, 14th Feb., '64.
The mark left by a drip underneath the handle/recess can also be made out in the photo above.
19th December
New Musical Express, 1st May, 1964. Vox advert for the Poll Winners Concert. The images were first used as an ensemble in the Vox advert for the Dave Clark Five in February '64. Note that the "A.C. 50" is actually a T60.
New Musical Express, 16th April, 1965. Poll Winners Concert ad.
18th December
A note on AC100 output transformer connections - 8 and 15 ohm. Below, schemas of the three main types: early cathode bias (copper and black panel amps); later cathode bias (grey panel amps); fixed bias ("100W Amplifier" and AC100/2).
The output terminal block of serial number 392, later cathode biased.
In the schemas above, the position and colour of the wires from the transformers are given in their most common order. In all types of AC100, however, one sometimes finds the common in the centre. The output transformers of early cathode biased amps have more complex windings (resulting in pairs of wires feeding into the terminal block).
AC100 Super Deluxe (SDL) speaker cabinets; 2 x 15" bass units; and the majority of Foundation Bass cabs had an impedance of 8 ohms, naturally requiring the output connections to be set for 8 ohms on the amplifier too.
By early 1965, a 470 ohm resistor was introduced across the 8 ohm tap to help guard against open circuits.
Detail from the "100W Amplifier" circuit of late summer 1965. L/S is "loudspeaker".
Effectively, when no speaker cabinet is connected, the 470 ohm resistor provides a load that the amplifier cannot "drive" - a sort of surrogate if you like (impedance is not identical with resistance) for a 470 ohm cab, not quite a dead short, but close. The protection afforded by the resistor is necessarily short term - enough to give time for a switch off following the discovery that no speaker cabinet is attached - but it is protection nonetheless. Hiwatt used a similar resistor over its jack socket ouputs.
When a speaker cabinet is connected, the 470 ohm resistor lies in parallel with the 8 ohm load of the cab. The effect of the resistor then becomes negligible. The product of the two resistances (one technically an impedance) in parallel is a little over 7.8 ohms.
16th December (2)
A little more on tags - see the entry below, 15th December. A number of Scandinavian countries had laws in the 1960s and 1970s that made voltage selectors illegal. The selectors were consequently removed and the mains input hardwired for 225v. Ingeniously, the black and gold tags were sometimes used to fill the hole.
An AC50 from late 1965 / early 1966.
16th December
A note relating to early Jennings Musical Industries, not really germane to anything here, but interesting for process. Pictures of a largish trove of early Jennings catalogues, flyers and brochures, some not available elsewhere (web or in print), may follow.
A good selection of catalogues, flyers and pricelists accompanied this letter, sent to the enquirer, who lived in Scarborough, in November 1961. A further batch was forwarded in 1962.
Five Jennings Musical Industries patent applications, 1955-1963 - inventions of Les Hills and Derek Underdown for organ and guitar elements - can be found here.
A further two are: organ note generation (Les Hills, 1953); and electrical oscillation generator (Les Hills and Derek Underdown, 1951).
Use the menu at the side of those patent pages to find copies of the original documents and drawings. Various dates are recorded - of submission, deposition, approval.
Les Hills, the genius behind the T60 amplifier and numerous organ circuits, continued working and innovating for Vox through to "Vox Sound Equipment Limited" days - see the patent for a polyphonic keyboard voicing, January 1969, on the Vox Supreme website.
15th December
Scarce these days, but by no means unique, a couple of JMI tags for English-made equipment, on the left the early style (to the last third of 1964), on the right the style that followed (last third of 1964 to 1968). The one on the left, originally attached to AC50 no. 1101, will have been the type accompanying copper panelled AC80/100s (thanks to Martin for pointing that out).
AC50 no. 1101, diamond input, second third of 1964. The amp is gone, but shop price tag, JMI guarantee, envelope and tag survive.
A number of the later style tags are still on or with the amps they were issued with:
Above, AC50 no. 5619, from 1966.
Defiant no. 1102, from April 1967. Thanks to Paul for these pictures.
The tag was presumably redesigned - a third style/type - in the summer of 1968 to omit "JMI". The succeeding companies were "Vox Sound Equipment Limited" (summer 1968 to early 1970) and "Vox Sound Limited" (summer 1970 to early 1973).
A "Vox Sound Limited" Supreme (1972). Picture from donkey's years ago. Presumably the tag simply has VOX.
There is I think a late AC100 in Germany also with a tag, but the picture has decided not to let itself be found for the time being.
9th December
A better version now of the Vox advert following the NME Poll Winners Concert, May 1967 - the line-up was mainly new solid state Vox Supremes and Super Foundation Bass amps. The Queen's award for Industry had been awarded in April 1967 - see this page.
NME magazine, 13th May 1967. All the bands on the bill used the equipment supplied by Jennings (there are small pictures throughout the 13th May issue). In the quadrants of the circle going clockwise: Dusty Springfield at the NME Concert, 1965; equipment on stage, also 1965; the Beatles with a 7120, Abbey Road, April 1966; Cliff Richard at the 1967 concert.
8th December
A better version (below) of the Vox advert following the NME Poll Winners Concert, May 1966, now posted on at the Empire Pool, Wembley page.
NME magazine, 13th May, 1966. The AC100 is still the picture (four were supplied by Jennings for the concert). The glimpses of The Beatles, Stones, and Dusty Springfield are from the NME Poll Winners, 1965. Pictures from the '65 concert were also used for promotional purposes in the States.
2nd December
A new page begun on the equipment supplied by JMI for events at the Empire Pool, Wembley, 1964-1968.
The main front of the Empire Pool, 1st July 1967, fans arriving for the Monkees - equipment supplied by Vox.
A second page illustrating the equipment supplied to smaller venues and events to follow.