Vox AC30 website updates

July 2022

31st July

Just to make clear in relation to yesterday's entry that Burnham Engineering was contracted to manufacture the metalwork of the chassis alone. Assembly of the electronics - wiring, fitting of the hardware, and so on - was done at Dartford Road. This was in contrast to Westrex and Burndept, which respectively not only did their own metal fabrication, but also electronic and hardware assembly from start to finish.

30th July

From the register of new companies, a note of the incorporation of Burnham Engineering - properly speaking "Burnham Precision Engineering (Dartford) Limited". Lawson Road was a spur off Burnham Road.

As is well known, Burnham produced various runs of chassis for JMI, as well as casings for footswitches and effects. One way to spot a Burnham-made AC30 chassis - most AC30/4s and some early AC30/6s - is by the presence of circular holes for the slider board fixings. Westrex and Burndept-made chassis have square cut-outs for cage nuts.

Also to mention in passing that Burnham-made AC30 chassis generally only have four fixing points - two on the front lip and two on the back. Westrex and Burndept provided five (two at the front, three at the back).

A late TV Front AC30/4.

Serial number 5002.

26th July

Some notes further to yesterday's entry. In early 1959, Tom moved ownership of (re-registered) the trade marks held by "Jennings Musical Instruments Limited" to "Jennings Musical Industries Limited". The Patent Office records do not give a reason (common practice).

But he was clearly happy enough for "Jennings Musical Instruments Limited" to remain in the records while business went on (from the summer of 1956) under the name of "Jennings Musical Industries Limited". Re-registering was not expensive.

But why the change of name at all? It is reported anecdotally that Tom liked the parallel with EMI - "Electric and Musical Industries Limited". But EMI had been around since the 1930s. One possible motivation was the need and desire to expand - a new factory and a new name, as mentioned .

"Mechanical World and Engineering Record", February 1956.

The rebuilding did not go ahead (nor for that matter did at least two subsequent schemes), but the name of the company was easy enough to change. If one looks closely at the emblem illustrated in full in yesterday's entry, the words "Trade Mark" can clearly be seen. This was evidently purely a public rather than legal declaration. No trade mark for the name "Jennings Musical Industries Limited" or "JMI" exists in the Patent Office records, and the name does not appear (as mentioned above) at all until as a registrant in 1959.

30th June, 1956.

A second search through the names of all companies created in 1956 (16,895 in total) simply re-affirmed the results of previous searches: Tom did not register "Jennings Musical Industries Limited" in that year. Nor did he do so in previous years or years up to 1960.

The page on has been adjusted and will be updated shortly.

24th July

Currently the earliest known instance of Tom's use of "Jennings Musical Industries Limited" is 30th June, 1956. Up to that point "Jennings Musical Instruments Limited" had normally been the company referenced (alongside the "Jennings Organ Company" and "Jennings Accordion Company").

Searches through official records of company registrations have so far brought to light only two relevant notices in relation to Jennings: the formation of "Jennings Musical Instruments Limited" in 1949 (as noted ), and recently "Jennings Musical Industries (Sales) Limited" on 13th June, 1960.

30th June, 1956.

Published on 25th June, 1960.

The normal procedure in the registration of "Sales" companies was to issue one share each to two named subscribers (for the registration records) and to leave the naming of directors for a later time - the names generally submitted in correspondence. Robert Valentine, who worked for JMI between 1958 and 1963, thinks that Doreen Crossley and Anne McFarlane may have worked on the assembly lines. They will have supplied the names of the directors - Tom and Joan Jennings - to Companies House.

Quite what purpose "Jennings Musical Industries (Sales) Limited" served is not clear. The company remained on the Register through to 1975, though had presumably been dormant at least since 1968.

As for plain old "Jennings Musical Industries Limited", first used in 1956, it may be that this was simply the trading name of "Jennings Musical Instruments Limited" for a time. Trading names did not need to be registered at Companies House, though without registration there was no protection in law if someone decided to pirate it. More doubtless to come.

21st July

The formal registration of Triumph Electronics as a company from a tightly-bound official register. Triumph did a good amount of contract work for JMI throughout the 1960s, principally assembling the chassis of the AC2/AC4, AC10, AC50, AC100, Vox metal-clad public address amplifiers, and the 7-series, though some "prototyping" was involved too. Quite where or how Derek or perhaps Dick met Geoff Johnson, the owner, is unrecorded - probably at a Trade Fair.

Whether the date of incorporation - 13th May 1960 - means that Triumph played little or no part in the development of the AC30 Twin is hard to say. Formal incorporation did not always align with start of business/trading.

William Barrington-Coupe, named as a Director along with Geoff, was a recording agent (mostly of classical music) and founder of the Delta Record Company. Unfortunately to prop up Delta's ailing finances, he began importing and selling radios from Hong Kong, and having neglected to pay tax, was caught and sentenced to jail.

Triumph later acquired 122 Brighton Road. Its premises were never large though. Amplifiers were assembled for JMI in the basement rooms. Other floors were set aside for adminstration and the rest of the business - the manufacture of precision electronic instrumentation for hospitals and universities.

20th July

Circuit diagram OS/013, drawn in November 1969, the earliest surviving sheet (so far) for the AC30 with integrated Top Boost: an image of the whole for orientation, and a larger detail of the Top Boost circuit itself.

A second copy of the sheet survives, not singed as this one is, but generally less distinct.

The original company name in the panel will have been "Vox Sound Equipment Limited". When "Vox Sound Limited" came into being in January 1970, many of the sheets were adjusted accordingly.

19th July

THE FIRST GREY PANEL CHASSIS WITH TOP BOOST CONTROLS IN PANEL - preliminary notes.

As part of the move to the new-style grey control panels, JMI handed production of Top Boost chassis over to Burndept. Burndept, as standard practice, stamped its chassis with numbers, indicating the voicing with a flash of paint and legend stamped in red. The colour for units with in-panel Top Boost was green, the legend "T/B Boost" (Treble/Bass Boost). See .

As mentioned yesterday, there was naturally some "cross-over" - at least one Burndept-made chassis was given a copper panel. By the same token, at least two Westrex-made units survive with a grey panel - AC30 Super Twin serial number 2673TB, and another serial number unknown.

AC30 Super Twin serial number 2763T, grey control panel, chassis assembled by Westrex, stamped "T.B." at left.

Serial number unknown. Chassis assembled by Westrex. Grey control panel with integrated Top Boost controls. As above, "T.B." stamped on the preamp upright. Note "165" in red crayon. The same writer wrote this and other numbers (119, 130) on various other JMI amplifiers.

Known early examples of Burndept-made Top Boost chassis, arranged below in order of chassis number, are:

unknown - Twin, chassis 3916. No component date codes visible.

2901TB - Super Twin, chassis 4476, Mullard capacitors with date codes "D3N", "A4N", "14N".

unknown - Twin, chassis 4530, Mullard caps with "14N" (1st quarter of 1964).

12411TB - Twin, chassis 4551, Mullards "A/64" and "14N".

11657TB - Twin, chassis 4616, Mullards "14N".

12019T - Twin, chassis 4630, Mullards "D3N", "A4N", "14N".

2739T - Super Twin, chassis 5214, Hunts cap. "WYT" = 10th week 1964, and main preamp filter = "WHT" 12th week 1964; three Mullards with "B4N" .

12405TB - Twin, external shots only.

This list could naturally be extended if Twins with serial numbers in the 13000s or higher and Super Twins with numbers in the 3000s and higher were to be included.

Evidence from grey panel AC30 Expanded Frequency is a little lacking at the moment. As noted elsewhere on this site, the new serial number sequence, which corresponds pretty much with introduction of grey panels, began at 500 and stretched into the low 600s before the model was deleted from the catalogue. The highest number known at present is 604 [* not 593 as previously stated]. See .

18th July

COPPER PANEL CHASSIS WITH TOP BOOST CONTROLS IN PANEL (2): As mentioned yesterday, Westrex alone originally produced these chassis. Burndept concentrated on Normal, Bass, and Treble runs.

Corresponding with the introduction of grey panels, Burndept took over the assembly of chassis with integrated Boost controls too. Seemingly there is at least one "cross-over" amp though - produced by Burndept (chassis number 4690) but with a copper panel.

The number of copper panel chassis made: 100 has for years been the estimate most often quoted and the figure regularly cited when an amp comes up for sale ("only 100 made!"); 500 has also been supposed, but that seems to be based on at least one wrong hypothesis. 500 in any case would be almost one in four AC30s during the period concerned.

Serial numbers are of no particular help. In terms of known survivors (for which photographs are to hand), the figures are:

AC30X: 17.

AC30 Super Twin: 5.

AC30 Twin: 10 (updated) - this includes photos (Jan. 1964) of three issued to The Shadows; and photos of two (April 1964) issued to the Rolling Stones.

Chassis not in their original box: 3.

Where Super Twin amplifier sections with such chassis are concerned we have: - serial numbers 10346, 2583TB, 2690 (not designated Top Boost on its plate however), and an amplifier issued with a pair of Line Source 40 public address speakers. It may be that AC30 public address sets of this sort were not uncommon. A chassis currently in a Super Twin box with a serial plate bearing the number 12897 does not belong (ie. was not sent out from factory) in it.

Additionally - a chassis also figures in AC30 Twin serial number 12397 (no voicing designated on the plate). The chassis now in the Super Twin box with serial number 2592TB does not belong there. The box has Top Boost controls on its back panel.

The question of how many chassis were made remains though. Perhaps around 100 is correct. But there may well have been more.

Note that as far as can be determined all copper panel chassis with integral Top Boost controls have 50R bias resistors.

17th July

Some notes preliminary to a new page (or pages) on AC30s with Top Boost controls integrated in their control panels (the AC30TB) - copper and grey.

COPPER PANEL CHASSIS WITH TOP BOOST CONTROLS IN PANEL (1) These were made by Westrex. Components for the most part have date codes from summer 1963 ("UF" to "UH" - June to August). Manufacture took place either in very late 1963 or early 1964. The "Expanded Frequency" AC30 (AC30X), which normally incorporated such chassis, was advertised for the first time in February 1964.

In terms of serial numbers, the lowest that have come to light so far are 10346 and 10348.

Detail of AC30 Super Twin serial number 10346. The Top Boost controls (Treble and Bass) are the two to the left of the Tone Cut (furthest right).

Detail of the underchassis of AC30 Twin serial number 10348. Westrex marked these chassis with an "X" in a circle. This one has year of manufacture: - "64".

No JMI circuit diagram is currently known for the AC30TB. The earliest we have is OS/013 (two copies only), drawn up either in January or November 1969 by "Vox Sound Equipment Limited". One of the copies is marked "Serial number 9619. Modified". 9619 is a JMI number, not part of a sequence ever used by VSEL.

Wallets of circuit diagrams supplied to repairmen by JMI generally only had sheets for the AC30 Normal, Treble, and Bass, along with OS/010 for the *add-on* Top Boost circuit.

Serial number 11913 - an AC30X - is the highest number encountered to date for a copper panel with integral Top Boost controls. Sales of the AC30X were fairly slow, so it evidently took a while for stock to move from Dartford Road. Serial numbers were generally assigned at point of despatch.

16th July (2) and (3)

12th August The entry on Alan Pyne, with some additions, has now been set up on a page of its own - .

16th July

AC30 Super Twin serial number 5645, the highest number encountered for a Super Twin so far. The next earliest is 5600.

The amp below, fairly extensively renovated, has an Albion mains transformer and a Woden output with the date code "BZ" = February 1968.

In terms of the wider picture, a little over 3000 Super Twins and Super Reverb Twins were produced following the introduction of the new serial number sequence (beginning at 2500) - probably around twice as many Super Twins as Super Reverbs.

The point at which the new sequence came into play is hard to pin down accurately at present - early 1964 seems most likely given the appearance of amps fairly early on with Top Boost integrated in their control panels. But some of the chassis and speaker cabinets seem older - serial number 2501 for instance has TCC capacitors dated December 1962; and the speaker cabinet of serial number 2599 contains speakers dated June '63.

AC30 Super Twin serial number 5645.

15th July (2)

Added to the new page on - Note in the image below that the holes for the end handles lie just inside the lines of piping. Simply good luck? Or were the channels for the piping arranged (when the split-front cabs were being designed in late 1960) in such a way as to allow room for the fixing points? The handles were purchased by JMI "off the shelf". No point putting the piping in only to find that four screw holes punctured it.

Serial number unknown, late 1962 / early 1963.

15th July

A page has now been started on on AC30 cabinets, for the time being in the period late 1960-1964. The picture will be extended forward to 1968 (probably not too much to add) and back to the 1950s in due course.

The standard form of logo.

14th July

A detail from an extremely well-thumbed copy of the JMI fold-out "Precision in Sound" catalogue from the autumn of 1963, Hank Marvin and The Shadows on the front. This is the first instance, where catalogues are concerned, of an AC30 with new SBU plastic handles.

Amps with new-style handles appear some months earlier though in promotional photos taken for JMI by Dezo Hoffman and others (in late June '63). The earliest non-promotional glimpse encountered so far is 11th May, The Rolling Stones at the Battersea Park Fair - picture (entry for 28th Nov.).

Autumn 1963.

11th July

Recently come to light, Vox AC30 Top Boost Reverb serial number 1285, assembled in Hastings/St-Leonards-on-Sea late 1972 / early 1973, the highest number to date, very close to end of days for the original incarnation of "Vox Sound Limited".

VSL AC30 TBR serial number 1285. The highest number previously was 1237.

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10th July

There is now a new page on the . As ever, this will be expanded as time goes on. Simply to note in passing that in 1964, several AC30 Treble chassis were fitted with add-on Top Boost units - presumably for further levels of cutting brightness.

Below, a detail of the Top Boost assembly of AC30 serial number 6948 to show the date code on the pot - "KK" = November 1963. At present, this is the earliest assembly with some indication of date to have been pictured. The units in AC30 Super Twin serial numbers 5311 and 5329, and a third, serial number unknown, are likely to be earlier still however.

Serial number 6948. The white control knobs were also used on certain models of Vox guitar.

9th July

Surprisingly few early AC30 Twins with factory-fitted Top Boost units on their back panels survive: serial numbers 4995 (?), 5080 (?), 6948, and a handful of others through to 1964, the point at which it became possible to buy an AC30 with the controls integrated in the control panel.

One of the main pots in serial number 6948 has the date code "AK" = January 1963; the pots in the Top Boost add-on - "KK" = November 1963. It is likely that the amp was later returned to factory for the fitting.

AC30 Twins issued to bands in 1963 all tend to have back-panel Top Boost: - those given to The Beatles, Shadows, Rolling Stones, and so on.

At present, the earliest securely dated instance of a Twin with factory Top Boost on its back panel is George Harrison's first AC30, Cavern Club, Liverpool, 22nd August, 1962.

The serial number of the amp is likely to have been in the 5000s. One of the knobs is already missing.

AC30 Super Twins with back-panel Top Boost are slightly more plentiful - the add-on unit was originally designed for the model. One does need to tread carefully though. There are quite a lot of home-made and repro units around. A shortlist of amps with original fittings will be posted shortly.

8th July

A new page has been started on the . At present, the earliest Twin to have been given a factory-supplied (probably factory-fitted) unit seems to be AC30 serial number 6948. A shortlist of other Twins to follow.

7th July

Some illustrative extracts from JMI OS/002 for "Amplifier Model A.C.1" - the AC1/15, first circuit. The original diagram for the amplifier is dated 4th April 1958 but un-numbered.

OS/002, dated 10th November, 1958, is an update and revision. The voicing of the input stage is modified (more treble), and among other things, plate voltages added for the EL84s.

Something very strange is going on with the HT voltage though: 400v before the choke; 340v after it (!); and 300v after the output transformer (!). The principal question is why start with an HT of 400v if the intention was to provide 300v for the EL84s and around 200v for the preamp - assuming that 400v after rectification is indeed correct?

One answer might be that the transformer was actually designed for a different application - a Jennings organ power pack perhaps - and that Dick and Derek felt obliged to find a use for unused stock. But that remains to be seen.

Date of the revised sheet, signed off by Derek Underdown.

Information panel with sheet number.

Upper right, detail.

OS/002 has been known for some time but laying hands on an original sheet has taken a while. This copy came with the wallet illustrated in yesterday's entry.

The nature of the changes to the preamp should help in the dating of any early (relatively unrestored) AC1/15s that turn up. The page on first circuit AC1/15s will be updated shortly.

6th July

Below, a shot of a wallet of circuit diagrams, one of five currently known. These were issued by JMI to its engineers and sometimes sent out to repair shops. Twelve sheets survive in this one.

One of the sheets encompassed is OS/010 - the Top Boost circuit drawn out by John Bell in December 1961.

It always pays to look closely at these diagrams as it is clear that different versions were printed up, some for general circulation, others not.

It turns out that at least four versions of OS/010 were issued: (1) as originally drawn by Bell in December 1961; (2) as contained in the wallet pictured above; (3) an adjusted copy of (2) embodied in the Thomas Organ amplifier service manual; and (4) the one currently in circulation on the web. No copy of (1) has so far come to light.

(2) OS/010 from the wallet. The HT voltage is given as 230v. An addition of 19th June, 1963, is signalled, but there is no note of what it was. There is no legend inside the panel, top right.

(3) Thomas Organ, sent to the States in late 1964. "OS/010" is re-written; HT voltage is 230v; reference to the AC30/6 and circuit diagram A/026 has been added at the foot of the panel, top right.

(4) The version common on the web. HT voltage is given as 320v. The substance of the addition of 19th June, 1963, is itemised: "Voltages and Pin Nos added". The legend "Vox Top Boost Mod" was added in the 1990s (the identity of the writer is known).

5th July

An interesting advert from November 1971 - the Vox shop in Gees Court (off Oxford Street) selling off storage-soiled goods. The AC30s were a real bargain.

At this point, production was divided between Hastings/St-Leonards-on-Sea (the Birch-Stolec factory) and the E.M.E. works in Italy (probably the new purpose-built complex at Montecassiano). E.M.E, which stands for "Elettronica Musicale Europea", a venture set in motion by Tom Jennings, Joe Benaron, and Enrico Uncini (of Eko), not only supplied neighbouring European countries with AC30s in the period 1968-1972, but acted as distributor for the "Vox Sound Limited" solid state amps built in England.

Most of the AC30s sold in England in 1971 will have been made in Sussex though. Batches are only likely to have been brought over from Italy when the occasion demanded.

27th November, 1971. A page on the Vox Discotape (Discotheque) can be found on the .

4th July (2)

Ported over from the Vox AC50 website. Pictures show that the new AC50 amplifiers issued to The Beatles in time for their Christmas concerts at the Finsbury Park Astoria (24th December, 1963 to 11th January, 1964) were initially accompanied by AC30 Super Twin speaker cabinets. Whether these were closed or semi-open back is unknown at present. At some point during the concerts - probably in the first days of 1964 - new speaker cabinets were supplied. These were the ones taken to France and America later in January and in February 1964 - full cloth (valance) fronts, Midax horn accompanying the two Celestion blues.

The page on (on the Vox AC50 website) has now been updated.

Early show - AC30 Super Twin speaker cabinets (one each for John and George) with split front. On the steps Paul's AC80/100 amplifier section and George's AC50.

A later show - both John and George have the new speaker cabinets with full cloth fronts.

4th July

Below, a note on Reg Clark, formerly General Sales Manager of JMI and VSEL. When VSEL collapsed in December 1969, Reg left for Dallas taking with him four key members of VSEL's sales team. In the 1970s he saved Vox twice, persuading Dallas-Arbiter to take on production in summer 1973, then CBS-Dallas/Arbiter (winter 1974). And Reg is also likely to have been behind the talks of a takeover in January 1970. Those unfortunately came to nothing.

In terms of the note, mention of the factory in Erith is intriguing. Could this be the old Vox works - the West Street Works - which had been vacated by "Vox Sound Limited" in early Spring 1971? It certainly seems possible, though if Dallas had acquired the building (at Reg's prompting), it will only have been used for a couple of years or so. In Spring 1973 the decision was taken to integrate all Dallas product lines in a vast new complex in Shoeburyness - see this page.

At any rate, word has it that Hayman drums were produced for Dallas in Erith. When further info comes to light, it will be posted here.

8th July 1972.

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