Vox AC30 website updates

June and July 2023

31st July

Thanks to Ian, a shot of a Woden mains transformer from a set in a Filmosound projector amplifier - date code "EX" = May 1966. Earlier Filmosounds (as made in the UK) often had Wodens with green shrouds, much as those in Vox AC30s and so on up to Spring 1964, and chassis with copper-coloured control panels.

The link is likely to be Westrex - assembling the Filmosounds in the UK under contract for the Rank Organisation / Bell and Howell.

Woden mains transformer in a Filmosound (projector) amplifier, date code "EX" = May 1966.

26th July

Thanks to Glen Lambert, there is now a page on , 1960 to c. 1966 - an important diagnostic aid in the often tricky business of determining the date of single speaker amps as well as Twins.

A "Type 1" panel.

22nd July

A detail from a single speaker AC10 with a serial number in the mid 4000s (mid 1964) - its original mains transformer replaced with a Woden, date code "JZ" = September 1968 [not 1967 as previously stated], presumably supplied by VSEL.

Part number 96714. It may be that the stock replacement output transformer and choke (not required for this amp) were 96715 and 96716. The Thomas Organ part numbers were 09-5101-0 (mains), 09-5102-0 (output); and 09-5103-0 (choke).

20th July

The new page on the has been expanded a little further. Further entries will be added soon - principally amps with serial numbers in the 4000s, taking the picture up to the point at which the serial number sequence was restarted at 1000 (in 1964).

Serial number 4154 - its fawn covering is probably recent and not original from factory. My mistake. That has been corrected on the page.

Below, the earliest firmly dated instance of the promotional image for the AC10 Twin to have come to light so far: - an advert printed in a British music trade journal, July 1962, ie. shortly before the Russell Hotel Trade Fair.

Detail from a page published in July 1962. The advert was later changed slightly to form the flyer issued in early 1963. The version below (entry for 18th July) has additions specific to the Trade Fair.

In terms of the move to split-front cabinets, the brochure of mid 1961 appears to be the earliest instance for the AC10 (single speaker model only at this time):

Page 6. The Vox AC10.

The earliest surviving AC10 (known at present) in this new style cab is serial number 3433.

19th July

A page has now been started on the . A second page will follow on the period 1964 to 1967. At some point it may be useful to gather the AC15 Twins onto a page of their own too. At present Twins and single speaker AC15s are laid out as a single sequence - .

18th July (2)

The JMI flyer issued to accompany the Russell Hotel Trade Fair of August 1962. The new boys (both displayed at the Fair) were the T60 Bass amplifier and the Transonic.

JMI flyer, late 1962.

18th July

The AC10 Twin was first brought to market by JMI in the late autumn of 1961 in company with the new AC15 Twin and AC30 Super Twins, publicity confined initially to typescript announcements and pricelists - and presumably display in the Jennings shop at 100 Charing Cross Road. In 1961 there was no Russell Hotel Trade Fair. Manufacturers were left to their own devices. Curiously Jennings did not list the AC10 Twin in its pricelists in Melody Maker magazine until May 1962. Perhaps no-one thought to update the roster of amps encompassed.

The first image, reprinted in various flyers through to 1963, probably stems from around the same time (Spring '62):

Announcement from the late autumn of 1961.

Detail from a flyer of early 1963. A similar flyer from late 1962 (printed to accompany the Russell Hotel Trade Fair) has the same drawing; and a further sheet is likely to have been the forerunner of that. Note the control knobs - apparently circular.

In October 1961, the AC10 Twin was listed by JMI at £56 and 15 shillings. This should really have been £57 and 15 shillings (55 guineas). The single speaker AC10 was pitched at £47 and 5 shillings (45 guineas).

In early 1963, the price of the Twin became 57 guineas, and that of the single speaker AC10 went up to 47 guineas - not inconsiderable amounts, though a good number of amps will have been sold on Hire Purchase (an initial deposit followed by a series of fixed monthly payments spread over 18 months).

17th July (2)

The highest chassis number for a Burndept-made AC10, 1964 to 1965, appears to be 2312 at present (the picture is a little indistinct) - somewhere around 1400-1500 in total probably assembled by the company. Chassis number 2200 on another amp is certain. Most of the rest - around 500 - were made by Westrex, though a small batch or two was produced in this period by Triumph.

At first, Burndept stamped its chassis numbers on top of the plinth, as it did also on the AC30 (the first 1000 or so it produced, autumn 1962 - mid 1963). Later, the number was stamped on the aluminium preamp upright underneath the voltage selector (as also on AC30s).

AC10 SER. No. 01280.

17th July

Production of the AC10 and AC15 in 1964 and early 1965: well over 2000 AC10s against around 800 AC15s. By 1965 JMI had evidently sensed that the AC15 was really no longer viable.

16th July

In the preamp of AC10 Twin serial number 2074, a Mullard mustard capacitor with the date code "D4" = last quarter of 1964. The last element of the code (the originating factory) is not visible.

Is this an indication that serial numbers c. 2000 - 3200 are all "1965 and later" AC10s? A brief search on Google turns up very few "1966" AC10s - only two in fact, the pictures of one unfortunately showing no obvious date codes of any sort; the other dated on the basis of its transformer part numbers (which are not in themselves date codes). The latest true date code visible on the amp's chassis is a Mullard cap "C4N" - third quarter of 1964.

For the time being it seems reasonable to assume that most later AC10s were assembled in late 1964 and 1965, but remained at the West Works for some time before being sold. Quite how many were lost in the fire of December 1965 is not possible to say at the moment. No lacunae look to be evident - so far as one can tell - in the sequence as it stands.

The provisional outline below has been adjusted.

15th July

Some general and still provisional notes on the production of AC10s from late 1961 through to 1965:

Serial numbers c. 3490 to c. 4500: Split front cabinets. AC10 single speaker amps as well as twins, and from early 1963, AC10 Super Reverb Twins. Chassis produced by Triumph Electronics and Westrex. Grey Goodmans speakers initially, then blue Elacs. The earliest known twin at present is serial no. 3526. From the 3600s certain Twins and (later on) Super Reverb Twins were covered in black vinyl. The latest fawn twin is serial number 4154. Some amps - serial numbers in the high 4200s through into the 4400s - have plates with the designation "N" = normal voicing, as if there were a bass version.

Serial numbers c. 4500 to c. 4700: Late 1964. The last of the single speaker AC10s. Some copper panel, others grey. Blue or silver Elac speakers.

Serial numbers 1000 - c. 1300: Mid to late 1964. Twins and Super Reverb Twins split away into a new numerical sequence. Copper panel, normally blue Elac speakers.

Serial numbers c. 1300 - 3200: Late 1964 into early 1965 (and beyond). AC10 Twins and AC10 Super Reverb Twins, grey panel, black grille cloth, silver Elac speakers. Chassis produced by Burndept and Westrex. Note that from 3000, numbers overlap with those assigned to the earliest AC10s.

Serial numbers in the 3200s: Early 1965. Slope-sided AC10 Super Reverb Twins mostly sold in Europe and America. The AC10 SRT is electronically much as the Domino Super Reverb, chassis assembled by Westrex; and Westrex also assembled the slope-sided AC10 Super Reverb Twin chassis.

There are various ways of sub-dividing these ranges in terms of cosmetics and electronics - more to come shortly. AC10s remained in the Vox catalogue through to 1967. So far, however, no component date code later than the last quarter of 1964 [not the third quarter as previously stated] has come to light. Naturally, this may change.

At present, two scenarios are possible: (1) that the sub-contractors ordered huge numbers of components in 1964 which kept production going through to 1967; (2) that AC10s were massively over-produced in late 1964 and early 1965 and took some time to sell - a state of affairs not helped by the deletion of the AC10 from American catalogues following the introduction of the Thomas Organ solid state amps (in late '65). JMI may have been left with a large amount of stock earmarked for the USA on its hands.

Of these (2) seems mostly likely.

14th July

Thanks to Glen, a shot of the serial number plate of AC30 Super Twin serial number 4287 TB, "TB" (as ever) hand stamped.

11th July

Thanks to Marc, the serial number plate of AC30 Super Reverb Twin serial number 3570, stamped, uniquely so far, as "Super Twin", "Reverb Top Boost". In 1965 these amps were normally stamped "S/R" (or "S/T" "R"), though it has to be said that the designation was somewhat variable.

10th July

A detail of serial number 13270B, copper panel, silver Celestion T1088s, mid 1964, but with a later Woden mains transformer, date code "LY" = November 1967 - possibly a factory replacement. Thanks to Ihor for signalling the presence of the Woden.

Detail of the mains transformer of AC30 Twin serial number 13270B.

30th June

Simply for orientation for the time being, some material on Vox reverbs. Below, one of the earliest ads for the unit, 19th May, 1962, along with pics of a surviving example.

Repeated from the entry for 31st May, 2021, . The image of Cliff became a standard feature of flyers, brochures, and so on, in 1962 and 1963. Later promotional material often named the countries to which the Reverb had been exported.

Details of two "Cliff Richard" Reverbs, one from 1963 (upper two pictures), the other from late 1962. Chassis assembled by Burndept; transformers supplied by JD Electronics of Corsham in Wilts (part no. PT.303).

Below, a reverb module removed from an AC30 SRT. The double springs of its tank indicates 1965 or earlier.

29th June

The info panel of the original version of JMI sheet OS/011. The precise form of A62-005 has yet to be determined, safe to say for the time being that "62" indicates 1962.

Detail of the info panel of OS/011, first version.

In terms of detail, OS/011 of 1962 is evidently closer to OS/075 than the version of OS/011 that was redrawn in 1964 and reprinted by Jim Elyea in his "Schematics Portfolio". The date of OS/075 - January 1965 - is still a difficulty though.

In terms of general topology, OS/011 has an ECC82 and half an ECC83, and OS/075 an ECC81 and half an ECC83 - but that is simply a matter of adjusted gain structure.

OS/012 is a reverb unit for organs, the sheet drawn by John Bell and dated 27th February, 1962.

28th June (2)

It turns out that early sheets for the JMI reverb circuit do in fact survive - OS/011 (first version) and A62-005, both dated 30th January, 1962, neither with additions/changes. Details to be posted in due course.

In the meantime an index of known JMI circuit diagrams for early amps has been set up here - .

28th June

In relation to the entries recently posted on this page, a fairly major question overhangs: if the majority of surviving AC10 Super Twin Reverbs of 1963 to late 1964 were not built according to OS/026, what were they built to? The answer is straightforward: OS/008 for the main amplifier circuit (the "AC10 Amplifier No. 3") and a version of what was later drawn up as OS/075 for the add-on reverb (much as for the AC30).

To date early sheets for JMI's add-on reverb have not come to light - OS/075 is from January 1965. There will have been at least two: one for the circuit itself (1962 to late 1964), and one for the "mechanical" arrangement of the additional elements. And there will probably been others setting out the details of the back panel module, reverb pan, and so on. By 1966 the drawing for the spring unit was A/147.

From OS/011 - for the "Cliff Richard" stand-alone reverb unit - it is clear that the add-on circuit for amplifiers (as set out in OS/075) had been formulated by 30th January, 1962. AC30 Super Reverb Twins were first advertised in May 1962, AC10 Super Reverb Twins in February 1963. The question of whether any of the latter were built to OS/026 remains.

12th January 2024: the material embodied in the grey sections below has been gathered up in a more coherent form .

27th June

Glen Lambert has kindly pointed out that the circuit of the AC10 Super Reverb Twin as expressed in OS/026 is effectively a copy - with certain necessary adjustments - of the circuit of the Ampeg Reverberocket R12 of Spring 1961. See also . More to come shortly.

Quite why JMI should have copied this amp in early 1963 is not certain. One intriguing possibility however is that a Reverberocket either turned up in "Musicland", the Jennings shop in Bexleyheath, or at the main shop on the Charing Cross Road, and that Dick Denney heard it, liked it, and so copied its circuit.

Just to add that the Ampeg has a potentiometer for reverb depth/length. The "step" switch of OS/026 of February '63 - see the entry below - is a JMI thing.

26th June (2)

The AC10 Super Twin Reverb of early 1963: a four-position switch for its reverb - OFF, then three pre-set settings for the depth/length. Jennings had long used this form of switch for the selection of vibrato on certain models of Univox (OFF followed by three pre-sets).

In the AC10 the reverb control was known as "Reverb Expansion", the steps being fixed resistors of 200 ohms, 500 ohms, and 1K ohms. These pre-sets had been replaced by a 1K potentiometer at some point prior to January 1964.

The challenge is to find an early AC10 SRT that has two inputs and five control knobs, the one for reverb with step selection.

Detail from OS/026, first version, dated 13th February, 1963.

26th June

A little more on OS/071. The sheet differs from its predecessors in three main respects: (i) the circuit is expressed differently; (ii) no indications of voltages are given at any point; and (iii) no date of redaction is noted in the information panel. As far as this last point is concerned, early January 1965 seems most likely. OS/070, for the Vox wireless mic unit, is dated 31st December 1964, and OS/072, for the AC50 mark 3, is dated 7th January 1965.

Without voltages OS/071 can hardly have been much use to a repairman. What or rather who was it for?

Info panel of OS/071

25th June

A note on the mode of HT supply outlined in three versions of JMI circuit diagram OS/026 and in OS/71 - all for the Vox AC10 Super Reverb Twin (two inputs). The sheet allocated to the Vox Domino Super Reverb Twin - also designated OS/026 - is not accessible at present.

(1) OS/026 of 13th February, 1963 (original sheet): a single line from the rectifier valve via a 1K resistor to supply the EL84 screens, the output transformer (for the EL84 anodes), and the rest of the circuit.

(2) OS/026 reprinted by Jim Elyea as no. 8 in his "Schematics Portfolio": as above.

(3) OS/026 reprinted by Jim as no. 9 in his "Portfolio": a dedicated line (no resistor) from the rectifier to supply the OT (for the EL84 anodes). The EL84 screens and the rest of the circuit are supplied via a 1K resistor.

(4) OS/071 (scans on the web): as (1) and (2) above. The power rating of the 1K resistor is specified as being 10W. As noted yesterday, this diagram has some pretty colossal errors (elsewhere in the circuit).

Quite how many (if any) chassis were built according to (3) is not known at present. What is clear is that at least one more sheet must have existed for the AC10 SRT. The two diagrams reprinted by Jim Elyea were new in 1964 and bear two dates: 27th January, 1964, and 22nd October, 1964, which last coincides more or less with the release of the AC10 SRT with trapezoidal amplifier cabinet.

The 27th January is designated as [issue] 3; the 22nd October as [issue] 4. At present there is no surviving record of issue 2, which must have been drawn at some point between 13th February 1963 and 27th January 1964.

Detail of OS/026 reprinted by Jim Elyea as sheet 8 in his portfolio - (2) above. Sheet 9 (number 3 above) has exactly the same info panel.

The first version of OS/026 (13th Feb. 1963) and OS/071 with all its faults were evidently sent out to repairmen. The status of the two sheets reprinted by Jim is not certain.

24th June

Below, a detail of JMI circuit diagram OS/026, the original sheet for the AC/10 Super Reverb Twin, drawn by Mike Turner in February 1963.

Unusually, the circuit was redrawn several times eleven months later (in January 1964) by Albert Hogben - two slightly differing sheets both designated OS/026 for the AC10, one of which was redrawn yet again - and with a colossal error - as OS/071. A third OS/026 was allocated (also in January '64) to the Domino Super Reverb Twin. More to follow.

Detail of the first version of the service sheet OS/026.

Melody Maker magazine, 12th October, 1963
Melody Maker magazine, 12th October, 1963

"Melody Maker" magazine, 2nd February, 1963, promoting the new AC10 SRT. Prices of the amplifiers available from JMI are given beneath.

12th January 2024: the material embodied in the grey sections above has been gathered up in a more coherent form .

22nd June

A new page has been started on the amplifier, introduced in early 1964. Below, one of the only instances of a Jennings promotion for the amp - an overview for an electrical trade press journal (which carried pieces on the activities of JMI from time to time).

March 1964

20th June

Entries have been added for five AC30s with - numbers 8146, 8792, 8844, 8855 and 8857. Pictures will be provided in due course.

19th June

Just to note that Glen's page on has recently been updated with additional info on the circuits of the the early amps and on the make-up of the AC10 "Throwback" amps of late 1960 to early 1962.

17th June

Thanks to Ben, pics of AC30 serial number 10067N, latest dateable element the Woden mains transformer with "AV" = January 1964.

AC30 serial number 10067N.

16th June

An outline page on the five versions of the Vox AC10 produced by Jennings in the period late 1957 to early 1962 - principally as a adjunct to Glen's new pages, and broad brush for the time being. Further details will be slotted in soon.

15th June

Glen Lambert has updated his page on the Vox AC10 and Vox AC15 amplifiers built in line with the (OS/005) with some superb new sections and info - notably, on the characteristics of the two types of amp; the tone control arrangement; and the employment of plate (anode) resistors.

Rear view of a cream AC10 Amplifier No.2 with add-on tremolo.

14th June

A couple of additions to the page on AC30s with - number 9799B, probably ready for sale in very late 1963 / early 1964; and 9986B, sadly probably no longer intact.

13th June

Some additions to the pages on AC30s with serial numbers in the and - notably, 10309 (plate only); 10556 and 10586 (pictures); 10753 (entry for a Super Twin), and in the 12000s: numbers 12247L (entry for a "Transistor Lightweight 30"); 12558 (image of the Burndept stamp); and 12097 (entry for a Super Twin).

12th June

The plate of , sold on ebay in 2022, the amp from which it came probably no longer extant now.

11th June

Some additions to the pages on AC30s with serial numbers in the and - principally illustrative pictures added to existing text entries.

The entry for serial number 4447 on the page on evidently did not register on the 28th May. That has now been remedied.

3rd June

Just to signal the addition of a superb new page by Glen Lambert on - a must-read for anyone interested in the formative years of amplifier design and manufacture at Dartford Road. Further material on the AC10 to come soon.

2nd June

Another AC30 Twin no longer extant - , sold in 2022, parts later re-sold, others re-purposed.

The plate of 10325N, re-sold separately.

1st June

Some updates to the main pages coming soon. Below, serial number 7138, which sadly no longer exists. The cabinet, chassis, and speakers were, subsequent to the amp's sale on ebay, re-sold separately.

The chassis has Woden transformers and choke with "AU" date codes = January 1963.

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