Vox AC30 website updates
August 2022
30th August
A closer shot of the Model A organ power sections: on the left, the audio amplifier (30 watt) with its two EL34s; on the right the HT voltage and valve heater supply unit. Transformers were supplied by Haddon to Derek Underdown's specifications. Valves are a mixture of Brimar and Mullard. Audio output was driven to one or more external "tone cabinets", Jennings's name for speaker cabs. These came in a variety of sizes (the largest ones often as large as the organ itself) and contained arrays of speakers as required - from 18" bass drivers to Goodmans Midax and Trebax horns and anything in between.
Derek's 30 watt amplifier design, later taken up in the Vox AC2/30. In mid 1963, its bias circuit was reworked for the Vox AC50 mark 1.
The Power Pack circuit, as above, from the "Jennings Organ Company" service manual.
Work done by Derek in the 1950s paid dividends also in the 1960s. His experience was instrumental in the equipping and production of numerous Vox amplifiers and speaker cabs. Goodmans Midax horns, for instance, did not suddenly come into the picture in early 1964 as has sometimes been said. Derek knew them and had employed them years earlier.
29th August
Some notes on a note. Below, the info panel of a later version of OS/063, the repeat percussion circuit initially offered with certain off-shoots of the Vox Continental organ, here adjusted for incorporation in the Vox Guitar Organ. Just to say that the history of the Guitar Organ will be covered in Martin Kelly's forthcoming book on Vox Guitars - a truly eye-popping wealth of new material to come.
At any rate, one of the most distinctive features of OS/063 is its interstage transformers. Although no direct parallel has come to light so far, it should perhaps be said that certain "repeat percussion" circuits - sometimes termed "reiterators" - in Hammond organs also have them.
In terms of ruling possible "sources" out: the three (or more) repeat percussion circuits devised by Thomas Organ are very different. Nothing identifiably similar to JMI's seems to have been employed by Wurlitzer or Lowrey either. The search goes on.
To add that the person most likely to have been responsible for the JMI design is Alan Harding, who developed among other things the Vox wireless transmitter systems (1962-1967). Note though, as mentioned in the previous entry, that the sheet is signed off by Doug McDonald, a fellow member (with Alan) of the R&D team.
Detail of the info panel of OS/063, later recension, for the Vox Continental, Guitar Organ, and the Electric Accordion (released in August 1965).
28th August
A generator assembly (one octave) from the Jennings Model A organ from 1956. On top, the six ECC83s for the generation of the 12 notes of the octave, and on insulated bases, the variable mica capacitors for tuning ("tuning control trimmers"). On the underside, the capacitor and resistor arrays.
A fairly detailed guide to tuning Jennings organs was provided in the Service Manual by Derek Underdown, the introductory paragraphs of which are below.
A detail from the "Jennings Organ Company" Organ Service Manual, late 1950s.
27th August (3)
Returning to Vox Continentals for a moment, a note on the optional "Repeat Percussion" circuit. The JMI circuit diagram - OS/063 - was drawn out by Albert Hogben on 7th December 1964 and signed off by Doug McDonald of the R&D team. The earliest advert to mention the effect that has emerged so far is the "Precision in Sound" newspaper-format catalogue issued in September 1964 in the UK and not too much later (though in a slightly different form) in the USA.
There is no mention of the effect in the blue fold-out Continental brochure of 1964.
Detail of the info panel of OS/063.
Detail of the UK version of the "Precision in Sound" newspaper catalogue. The US version omits the Fender guitars and amplifiers offered by JMI in the UK.
27th August (2)
Corrected 3rd August - the" Model A" was in fact one of the first members of the "V-series", so the sheet below giving resistor and capacitor values is correct for it.
As a preliminary to pictures of one of the generator arrays in the Model A organ from 1956, a couple of sheets from an early "Jennings Organ Company" service manual. These were fairly lengthy loose-leaf books containing sets of pages on tuning, troubleshooting, as well as circuit diagrams for the various models of organ.
Below, a copy of OOS/001 - Oscillator no. 1 - which corresponds with the circuits in the Model A. The Oscillator no. 2 sheet is for the later "V-series" organs. Also, a detail from the list of capacitor and resistor values for the V-series generators, simply to show the general arrangement. The sheets for the earlier B-series are lacking.
Jennings Organ Company, sheet OOS/001. The text at right reads: "These components (C1, C2, C3, C4, R1, R2, R3) vary in value from oscillator to oscillator. The full range being shown in the accompanying lists."
Jennings Organ Company, service manual, capacitor and resistor arrays for the V-series organ generators.
27th August
Further pictures of David's Jennings Model A organ. For a general view of the front, see below, entry for 22nd August (2).
The rear: lowest level at left, the power amplifier (sound), with two EL34s; at right the voltage supply amplifier - termed the "Power Pack" by JMI - providing the HT voltage and 6.3v lines for the valve heaters. In the centre, the 8 ranks of generators for the 8 octaves of the keyboard. The generators each have six ECC83 (12AX7) valves - Mullards and Brimars - to produce the twelve notes of the octave, one half of an ECC83 per note (ECC83s embody two completely separate triodes in a single glass envelope). At top, the rear of the tone/stops assembly.
The white bar above the opening for the volume pedals is a heater - a "damp chaser". The note generators of valve organs are particularly prone to environmental changes, quickly falling out of tune.
Details of a generator array to come.
26th August (2)
A few more shots of "square top" Vox Continentals. First, well known, Mike Smith of the Dave Clark Five at the Tottenham Royal, residency late January to early February 1964, filmed by the Pathe Newsreel Company. This organ is not seen again after the stint at Royal, a new one with slope top having taken its place by Spring '64.
It is likely that the "square top" provided for the residency was issued to Mike in late 1963, perhaps from the Artists' Loan Shed at Dartford Road.
A screengrab from the Pathe footage - Vox logo stuck on.
A detail of a promotional picture taken at the Royal. The logos are airbrushed onto the original photo.
Second, Patrick Dane and the Quiet Five - a promotional picture from a concert programme from autumn 1964. Although the quality of the shot is only so-so, one can nonetheless make out the square top and perspex music stand. It is not known when the band acquired the organ.
Patrick Dane and The Quiet Five.
26th August
Simple text entries have been created (for the time being) for four more AC30s with serial numbers in the low 15000s: 15043T, 15058T, 15068T, and 15206T (simply the wooden case with serial number plate attached).
25th August (2)
A couple of great details from pictures taken by Harry Hammond - Al Saxon of the "Overlanders" at a very early "square top" Vox Continental organ with perspex music stand, probably early 1963. The key features, setting this organ apart from later square tops, are: (1) lid latches on the front edge; (2) the plain case, no silver "string" inset at the edges; (3) the absence of any "Vox Continental" plaque; (4) the absence of white piping on the front lip of the orange top; (5) the "diving boot" volume pedal (see this page); (6) the two jack sockets on the underside of the organ - one a pass-through for the pedal.
As production proceeded, the elements noted above were adjusted/updated - some separately, others together.
The Tornados and Sounds Incorporated also had early Continentals - the Tornados one of the first (in late December 1962), Sounds Inc. probably shortly after the Overlanders.
As has been mentioned on one of the recent new pages, later in production the lid catches on the front edge were moved to the sides, necessitating the manufacture of stands with shorter horizontal bars.
25th August
Just to note in relation to the Vox Continental that Jennings had hit upon the convenience of a 49-note keyboard some years earlier - in the summer of 1958, the organ in view being the "Model H", designed for chapels and home use. That the Model H was a valve-driven model rather than transistor makes no difference insofar as the electro-mechanical key contact assembly is concerned. As has been mentioned, Kimber-Allen was Jennings's main keyboard contractor in early years; but it is certainly possible that Herrburger had been brought in by or in mid 1958.
In many respects, Tom Jennings and Derek Underdown got going with the Continental at just the right time. A few months later, the world of transistor organs began to expand exponentially - doubtless prompted in part by their lead. Below, an advert for the Harmonics "Solette" from February 1963, old-fashioned switches for stops, not really a "Beat Group" organ as such, but equipped nonetheless with a recognisably Continental-style perspex music stand; and a note from April 1963 signalling coming meetings of the "Electronic Organ Constructor's Society".
Published February 1963. There is an interesting thread on Harmonics of Bromley here.
Published April 1963.
24th August (2)
The page on the early Continental keyboard has now been started - available here. As ever, further material to follow.
Keyboard assembly swung up on its hinges. The board encompasses four octaves.
24th August
Some new details, particularly of the generator boards, added to the page on the Vox Continental's electronics. Also, a general shot of the power section and vibrato board showing the replaced zener diode in position. Shots of the original, which had slipped considerably in value over the years, are included on the page linked above.
Early Vox Continental power section and vibrato board
In late 1963 JMI phased the simple voltage selector switch (115v/230v) out, replacing it with a red plastic selector plug - of the type used in AC4s and Vox Domino amplifiers - positioned behind the mains transformer (i.e. to the right of where the switch is in the early Continental above). The vibrato board was lengthened to 15 tags. These changes had certainly been introduced by serial number TC1094, possibly before. Serial number TC1089 still has the simple two-way switch however.
23rd August
A page has now been started on the fixtures and fittings on and in the early Continental case - available here.
22nd August (2)
Thanks to David, a picture of one of the first Jennings Model A organs produced, serial number A2, probably first half of 1956, designed for use in churches and chapels. It was bought new by a gentleman in Corby, Northants and later went to Weldon Congregational Church. Further details and info to follow.
Jennings Model A organ, first half of 1956.
22nd August
Some new entries added to the page on AC30s with serial numbers in the 15000s - mostly Trebles and Basses. There are very few "Normals" in the 15000s. The most peculiar of those recently added is an AC30 Super Twin with serial number 15273T. Super Twins had long had their own sequence. It is not immediately clear why this amp should be among the 15000s (unless perhaps the plate is from some other source). Further entries to come.
21st August (2)
Just to say that a new page has been set up on the electronics of the Vox Continental organ from mid 1963. It's fairly bare bones at the moment but will doubtless grow section by section. The next page - on the keyboard assembly - may be a little while coming.
21st August
A small update and correction to the new page linked below: the Vox Continental organ in view was actually purchased on the Charing Cross Road c. 1966, not c. 1969 as stated initially. It was used by the band "Nelson's Column", which opened for many big names at university gigs in the late 1960s: Cream, The Yardbirds, Tyrannosaurus Rex, Chicken Shack, and so on. Thanks to Chris, the band's guitarist and custodian of the organ for many years, for the info.
20th August
The first of a small set of pages on a Vox Continental organ from late May / early June 1963 - probably one of the first fifty made - has now been set up here. But for a couple of note generators which need tweaking, it works very well indeed.
Component date codes and matters relating to assembly and production will come into view with the pages on the electronics.
16th August
A detail from an AC30 output transformer made for JMI by Woden but not used in production. A batch of these was acquired by Alan Vale from a former member of JMI staff. They had been painted black.
Printed by Woden with JMI part number "67344", dated "KT" = September 1962.
There are several points of interest. First the JMI part number "67344". Woden normally numbered its transformers in a fixed order for Jennings: power transformer, then output, then choke. The set will therefore (notionally) have been 67343, 67344, and 67345.
Second, the transformer is early. The date code "KT" indicates September 1962. The previous set of Wodens - 66309, 66310 and 66311 - had been been ordered by JMI for use by Burndept in the summer of '62 - earliest date code "HT" = August 1962.
Third, the secondaries of "67444" are of the simpler type internally, single wires only emerging for the common, 8ohm and 16ohm taps - in this respect identical to the later set of Wodens used in production amps (76852, 76853, and 76854). 66310 has paired wires, following a more complex internal structure.
That JMI should have been exploring a cheaper set of transformers at such an early juncture is interesting. A simpler internal structure meant a cheaper unit. The more expensive set - 66309, 66310, 66311 - presumably won out on other counts.
So far there is no indication that 67343, 67344, or 67345 made their way together or separately into production amps.
15th August
Thanks to Benjamin, a great shot of the Westrex inspection tag on an early AC30 Super Twin amplifier section. The serial number line was not filled in of course because Westrex simply assembled the chassis. Box and serial number plate were provided at Dartford Road.
Late 1961 / early 1962.
12th August (2)
Just to note that text entries have been created for two early copper panel AC30s on this page: serial number 4917N, and a Super Twin amplifier section without a plate. Pictures to be supplied in due course.
12th August
The notes on Alan Pyne assembled last month have now been collected together in a more logical order on this page. Further examples of amplifiers will be added in due course, but kept to reasonable numbers as there are a good few around. So far, no example of a keyboard with a Pyne sticker has come to light though. Perhaps in time - keyboards were one of his specialities.
11th August
A detail from the JMI pricelist of early 1964. The Jennings Church Organs are still there, along with three models of Univox, the pedal units, and the Vox Continental. The Thomas section is now the largest though, a consequence of the deal that Tom and Joe Benaron of Thomas struck at the NAMM show in Chicago, July 1963. JMI would be "exclusive" distributors of Thomas organs in the UK. According to Rodney Angell, who worked in the Jennings Organ division from c. 1965-1968, one of the tacit conditions of the arrangement was that JMI had to reduce production of its own console organs.
JMI pricelist, early 1964 - printer's runner has "2/64".
10th August
Fibreboard case for the legs.
Vox Continental serial number TC1549, made at the Dartford Road works a few months before production was moved to Erith.
9th August
Below, a couple of details of the lid of a Vox Continental organ from late May / early June 1963. The latest date stamp on the electronic assemblies is 8th May 1963. The circuit does not include a change noted on the circuit diagram, 29th May.
It seemed worth putting the pics up for a couple of reasons. First, the original strap handle (now gone) was of the type initially fitted to AC30 Super Twins - either leather or black PVC with metal end clasps, 9 1/2 inches from centre to centre. Where AC30s are concerned, one begins to see the new SBU handles replacing the old strap handles at around the time this Continental was ready for sale - see this page.
Second, there do not seem to be any other images of Continental lids with early handles on the web. The cases for sets of Continental Z-legs were by nature too thin for new SBU handles, so either had luggage handles or small plastic strap handles.
Above, detail, Vox Continental, late May 1963.
Vox Continental, c. 1965
In terms of early pictures, the closest one gets to a Continental lidded up is this shot of the "Beat Chics", said have been taken on the 18th July, 1964.
8th August
Thanks to Glyn, pics of AC30 Super Twin serial number 11077, recently sold - a really nice amp. Chassis assembled by Westrex, latest visible date code October 1963. Date of the Celestions unknown. The serial number plate has "AMPLIFIER" at its head rather than "VOX AMPLIFIER". There is a strong likelihood that this amp was in the hands of its first owner by late December '63. Further pics on this page.
AC30 Super Twin serial number 11077N.
6th August
Recently sold on ebay in Germany, the plate from AC30 serial number 4800N (the "8" mis-stamped at first pass), a late black panel amp (AC30/6).
5th August
Thanks to Mark, pictures of AC30 serial number 6873N, probably mid 1963, the original footswitch still present. The amp, as can be seen, has been well used and is still in superb working order.
AC30 serial number 6873.
4th August
A correction added to the page on AC4s: one of the first mentions of the model came in a JMI pricelist of October 1961: the "A.C.4. Normal" at £19 and 19 shillings (19 guineas). The other amounts noted are the hire purchase terms: the initial deposit of £2.0.0, then twelve instalments of £1 15 shillings and 5 pence.
October 1961.
For most of 1962, the AC4 was regularly mentioned not by name but as a "2 Watt" amplifier. The AC2 on the other hand, just to mix things up, is termed a "4 Watt" amplifier in late 1960 and early 1961. A JMI catalogue of 1961 issued by "Musicland" (the Jennings shop in Bexleyheath) ups the ante, giving the AC2's power as a massive "6 Watts".
3rd August
A new page has been started on early AC4s, late 1961 [rather than 1962 as previously stated] - 1963. The amps in view all have beige/fawn vinyl. There is naturally some overlap with the page on the AC2, the AC4's predecessor.
From late 1961 through to the summer / autumn of 1963 around 800 beige-covered AC4s were produced, in rough outline serial numbers 2200 to 3000. One of the key changes was the introduction in early 1963 (probably Spring) of a mains transformer with selectable voltage: 110v / 230v. Tom clearly had the American market in view. He went to the NAMM show in Chicago for the first time in June '63.
The control panel of AC4 serial number 2974.
1st August
Two new pages have been set in motion: one on Burnham Engineering, the other on Westrex. Both are likely to grow, the one on Westrex more in relation to 1963/1964, the one on Burnham in relation to earlier days (the late 1950s).
Updates for October and November 2020.