30th January (2)

Further details from last week's conversation with a former JMI amplifier tester. In 1963, around twenty AC30s a day were tested and made ready for sale. The process was that when an order came in, Margaret and Janice would bring the necessary elements together - a completed cabinet with speakers, its back boards, a chassis, and so on. The chassis would not at this point be fixed in the cabinet.

Margaret and Janice then handed the amp over for testing. In 1963 there were three testers. The electronics would be checked, any faults put right, and the amp tested with guitar. The chassis was then fixed onto its slider board and the cabinet back boards screwed on. Once everything had been secured, the AC30 would be passed to Jack Jennings in Dispatch.

Early on, cabinets came mainly from Glock, some from Gla-Rev. A third company - "Hazel's" (further details to be supplied) - was not used for long as their cabinets were inferior to those of the other two.

Glock and Gla-Rev applied the vinyl covering and fitted the grille cloth and so on. Glock made its cabinets such that almost any back board fitted any body. Gla-Rev cabs generally had unique back boards. Gla-Rev chalked numbers on its cabs and boards so that if a cab's boards became separated they could be matched up again.

A page on cabinet makers can be found here.

30th January

Dick Denney was not the only one at JMI to prefer, as a general rule, Westrex-made chassis to those made by Burndept. The notes below are from a recent conversation with a former JMI employee, his principal duties being amp testing in the Dartford Road Works (more later).

(1) Burndept chassis sometimes had cold solder joints, a result of the speed with which the assemblers were urged to work by Dolly Clark. Dolly was chief overseer of the assembly benches at Burndept (she was employed by the company, not JMI). Westrex amps rarely had any such faults. Before the amps left the Dollis Hill factory, joints were checked by an inspector and marked in red.

(2) Westrex amps were generally just a little bit louder. Haddon and Albion transformers (used by Westrex) normally produced 285v (+) before rectification; Wodens (used by Burndept) around 280v. Voltages scaled up after rectification, giving Westrex the edge in terms of volume.

Denney was without a shadow of a doubt a great asset to JMI, but one has to be aware that he often channelled the opinions (and the work) of others.

29th January

Below, pics of serial number 5672, electronics untouched - i.e. as they were when the amp left the factory around fifty-eight years ago. The main Hunts filter capacitor has the date code "ITH" = 34th week of 1962 (end of August). The tone pot has "GJ" = August '62. Thanks to Kevin for the pictures.

28th January (3)

At some point in the second half of 1962, Burndept began passivating the steel plinths of its AC30 chassis to protect against rust. An electro-chemical process involving baths of nitric acid and salts, passivation creates a sealing layer of chromium oxide on the surface of the metal. Passivated chassis tend to have a yellow/gold appearance, and regularly present feint swirls of rainbow colours.

In the later 1960s Jennings and Burndept contracted "Holmes Plating" of Blackheath to do the specialist work of chassis passivation, and it may have been Holmes that did the work in the earlier 1960s too. The Works building in Blackheath Grove, before Holmes took it over, had been an ice-rink. Holmes was there from 1911-1987.

Westrex chassis tend not to be passivated.

The chassis of serial number 5937.

28th January (2)

A couple of pictures to show that the black and red print WIMAs used by Vox in 1962 and 1963 were both Tropyfol "F" (TFF). Later on Tropyfol "M" (TFM) was sometimes used.

Chassis from late 1962. Note the "F" on the black print 0.047uf caps.

Chassis from late Spring 1963. 0.047uf Tropyfol "F" caps again, but red print this time.

28th January

WIMA Durolit (paper and foil) 0.15uf, 630v coupling capacitors in serial number 5650, which was produced in the last third of 1962. Its Woden transformers have August 1962 date codes. The values are given on the capacitors in relatively small green/black print. Print size was increased in the later sixties.

Although Durolits were clearly available in the UK from the middle of 1962 (at the latest), there is no mention of the range in literature produced by Waycom Ltd early on. There is a reference in a trade journal of 1963 published by the Pergamon Press (Robert Maxwell's old company), but little else until the later sixties.

Coupling capacitors C6 and C9 as indexed on the AC30/6 circuit diagram OS/065.

27th January (2)

Waycom Limited is also likely to have been the source from which JMI acquired its WIMA Tropydur capacitors - "200,000 to 300,000 pieces always in London....".

"Wireless World", July 1960.

27th January

A few more notes on WIMA capacitors. First, an advert from "Wireless World", July 1961 - Tropydurs, the black ovoid WIMA caps used by Vox in 1960 and for a large part of 1961, offered by Smiths of Edgware Road in London. Prices are necessarily retail. Manufacturers would buy wholesale - i.e. with a discount (sometimes substantial) for bulk. Even so, values above 0.1uf will not have been inexpensive.

"Wireless World", July 1961.

In late 1960, English papers began advertising the new WIMA Tropyfols - polyester foil dielectric sealed in resin, gold-coloured bodies, black or red print. JMI began using these in late 1961 / early 1962, presumably bought from Waycom Ltd in London.

"Wireless World", December 1960.

"Wireless World", January 1961.

The front page of a WIMA brochure for the new Tropyfols, April 1960. Thanks to Marc for the copy.

In mid 1962, JMI began using larger WIMA Durolits - 0.15uf, 630v - as the main coupling caps between preamp and power section - C6 and C9 on OS/065, the circuit diagram for the AC30 "Normal" voicing. In 1960 and early 1961 - that is to say in the days when WIMA Tropydurs were used - these capacitors had been 0.01uf, 500v.

AC30/6 circuit diagram, OS/065 - coupling capacitors.

23rd January (2)

Currently for sale in Italy, AC30 serial number 22847, the highest JMI number known. The control panel is JMI too. As in the case of late JMI AC50s, the logo is of the type used for the solid state range from early 1967.

It well may be however that this amp was one of those that remained unsold when the company ceased trading, passing to "Vox Sound Equipment Limited" to be sold in the last third of 1968.

23rd January

Black-print WIMA capacitors. In AC30s produced in late 1961 and 1962, codes can regularly be seen on 400v WIMAs. Those observed so far are "P4", "Q1, "Q2" and "Q3". "P" and "Q" would seem to be the year, the number standing for the quarter. By 1968, WIMA had gone over to the Mullard system for small-value caps, "C8" standing, for instance, for third quarter of 1968.

It is tempting to take "P" as 1961, and "Q" as 1962. Red-print WIMA Tropyfoil (Tropyfol) have a different set of codes, so too the earlier black Tropydurs.

22nd January

Leaping ahead slightly, some preliminary notes on AC30s and the new companies 1968-1973.

Spring of 1968: JMI finally ceased trading, having been in the hands of the official receiver since December 1967.

Summer of '68: Cyril Windiate, who had taken over the running of JMI following Tom's dismissal in late 1967, Reg Clark, the General Sales Manager, and other former members of JMI staff worked together to recast the company as "Vox Sound Equipment Limited" - to produce and sell Vox equipment. VSEL bought in a good amount of unsold JMI stock (auctioned at the West Street Works in September 1968).

Mid 1968 - late 1969: Although VSEL principally sold solid state amplifiers, the AC30 and AC50 remained on the books, appearing in most of its catalogues and pricelists (a good many printed for European markets). Very few AC30s survive however with "Vox Sound Equipment Limited" serial number plates - for which there are good reasons, to be taken up later. The majority of solid state amps sold by the company had clear VSEL badging - control panels, serial number plates, supplied documentation, and so on.

Detail of a "Vox Sound Equipment Limited" brochure printed for the German market in Spring 1969. Note the new American style logo on the AC30 (also used on the JMI and VSEL solid state amps), and the single row of vents on top of the cabinet.

Early 1970 - 1973: "Vox Sound Equipment Limited" crashed in late 1969, having run into severe financial difficulties during the year. Reg Clark, who had taken a new position with Dallas Musical Limited (part of the John E. Dallas Group, not yet Dallas-CBS/Arbiter), tried to interest Dallas in taking Vox on, but talks came to nothing unfortunately. Some weeks later though in early 1970, Vox was re-formed as "Vox Sound Limited", thanks to the efforts of Michael Birch of Birch Electronics and George Stow of the Stow Group. The two later amalgamated their interests as the Birch-Stolec Group. George Stow became managing director of Vox. The AC30 remained in production.

VSL AC30s: Sometimes a peculiar breed. "Vox Sound Equipment Limited" speaker labels were regularly applied to new speakers - that is to say to speakers made by Celestion long after VSEL had folded. Old JMI transformers were fitted instead of the new ones supplied by "Twickenham Transformers" / "Lemark Electronics" (the old and new names of the transformer manufacturer overseen by George Stow's business Group since 1967). Dates were stamped on the new-style tag boards introduced in 1971 at the Birch-Stolec factory in Hastings - "VSL" moved production there in the summer of '71.

A detail of the preamp of AC30 serial number 25628, "Vox Sound Limited" on the serial number plate. The Mullard mustard caps have date codes "C9", "D9" and "B0" - third and last quarters of 1969, and second quarter of 1970.

Serial number 25628 again. JMI Haddon output transformer. The mains transformer and choke are old JMI Albions.

A detail of the preamp of serial number 30865, no company given on the plate, simply "Vox Amplifier" at the head. The board is stamped "6 72" = June 1972. The earliest stamp known at present on one of these new-style boards is "7 71" = July 1971.

The "Vox Sound Limited" inspection tag on an early 1970s AC30. Note the address "Hastings, Sussex" - ie. the Birch-Stolec factory. The three ink stamps suggest that the amp was sold c. 1973 or 1974 - "DMI" must mean "Dallas Musical Industries".

21st January

Below, pictures of a Radiospares 10H choke from the early 1960s alongside the type of choke used with increasingly regularity in AC30s assembled in 1965 and early 1966. Some good examples here - serial numbers 20269, 20523 and so on. The part number of this later type is 66429.

66429s were also used in the summer of 1965 for a run of new fixed bias AC100s built to the "100W Amplifier" circuit diagram - see the examples on this page. The one illustrated below is actually from one of these AC100s. No maker's mark is ever given; but there are often three-letter date codes stamped in white.

Although the frames (housings) are different, the formers are identical: five slots on one side, plain on the other but with a sort of tongue on top. It may be that the later chokes were also supplied by Radiospares.

Radiospares, however, was generally not a manufacturer - simply a commissioner of items made by others and branded with the Radiospares name. The principal manufacturer of the transformers supplied by the company is reckoned to be R.F.Gilson of Wimbledon (South London). But whether Gilson produced these chokes is unknown.

20th January (3)

Details of two of The Beatles' AC30s - John's and Paul's - October 1963. Both Beatles are plugged into the Brilliant Channel. John's volume is set at just short of 12 o'clock; Tone either at full on or full cut - probably the former. Paul's volume is at around 2 o'clock, Tone at full cut. Further pictures to follow.

20th January (2)

Super Twin amplifier section serial number 5156N (probably late 1961 / early 1962) has just come to light. Thanks to David for the picture and info.

20th January

Some pictures on this page of an untouched Westrex-made grey panel chassis from the third quarter of 1964. Latest visible dated components: the original ECC83s, May '64. It was in full working order (no attention required) in 2015.

19th January

Serial number 22117, produced in 1967 (probably the second half), owned by Dave Davies of the Kinks, sold on ebay in May 2007.

A screengrab from the ebay auction page.

18th January

A note on chokes in early AC30s (1960 and 1961). The earliest were standard Radiospares catalogue items. They accompanied Haddon mains and output transformers in AC30/4s and pre- and some post-LOC AC30/6s. In late 1961 Haddon produced its own choke, as did Albion (and Woden later on - late summer of 1962).

The AC30/4 and AC30/6 circuit diagrams both give the value as 10-20HY and 100MA. "HY" stands for "Henrys", the measure of inductance.

Detail from OS/065, the AC30/6 Normal voicing.

The outward facing side of the choke on an AC30/6 pre-LOC chassis.

The chassis side of the choke on another chassis, original label present: 20 Henrys, 500 ohms (DC resistance), 100 Ma.

The reason why the circuit diagram gives 10-20HY inductance becomes clear when one refers to the Radiospares catalogue of 1961: the two values were available in housings of the same size and format. If one was out of stock, the other could be used. As far as the schematic was concerned, JMI evidently thought it well to reference both (just in case), leaving the sheets uncorrected as copies were made. By the end of 1962 chokes were 19H.

Detail from the 1961 Radiospares catalogue.

1961 Radiospares catalogue cover.

Although no definitive example of a 10H choke has come to light so far in an early AC30, many are "unknowns" - only the outward facing side of the housing normally being recorded in pictures. Labels on the "inner" side are often discoloured or absent.

17th January

A new page on documents 1966 has been started. A page on the final AC30 Twins produced by JMI - serial numbers in the 22000s (1967 and early 1968) - will be posted soon.

16th January

An advert placed by Gamlins of Cardiff in the "Merthyr Express", early 1963. The list of amps (and prices) is similar to the one given in the JMI promotion for the new AC10 Super Reverb in "Melody Maker" magazine, February 1963 - see this page.

The T60 is at this point called the A.C.60 Transonic Bass. Two 2x15" speaker cabinets are recommended. Price: 145 guineas. The A.C.30 Super Transonic - a solid state T60 amplifier unit in a futuristic case (see the entry for 23rd December, below) - is 150 guineas.

15th January (2)

A page on AC30s with serial numbers in the range 20000-21000 - late 1965 through to 1967 - has now been started here.

15th January

Just to signal that the page on Burndept, Vox, and the West Street Works on the AC100 website has recently been updated (further updates there to come). A page of a slightly different nature will be set up here, referenced more specifically to AC30s. For the moment, details from two Ordnance Survey maps to show the position of the Works in Erith, and the address panel from a Burndept flyer of late 1964.

Although Burndept's principal business was telecommunications equipment, particularly for the aviation industry, the company manufactured a wide range of things - scientific instruments, domestic electronic goods, even at one time cookers. Contract work had been undertaken from the 1950s. By 1961 a controlling interest in Burndept had been taken by Royston Group of Companies; Vox was added to Royston's portfolio a year or so later - late 1962 / early 1963.

With the opening up of the American market in 1964, Vox had to expand. Burndept made space in its West Street Works (top floor and some rooms on the first), and over the course of around six months a wide range of activities were moved there from Dartford Road. Royston reported at its Annual General Meeting in July 1965 that the move was complete. One of the consequences of these changes was that the contract with Westrex was not renewed. The Burndept / Vox Works could provide the majority of amplifier chassis. Triumph Electronics, which had been brought in as a contractor in late 1963, retained a fairly limited brief (being a relatively small concern), however: AC50s, PA amplifers, and occasional runs of other things, notably in 1966 the 4-series and 7-series range.

Above, details from two Ordnance Survey maps of Erith.

Burndept flyer of late 1964. The telephone number of the West Street Works - ERITH 33080 (which became the Vox telephone number) - is crossed out and a new one typed on. Burndept retained most of the ground and some of the first floor of the building for its own operations, making over the second (top floor) entirely to JMI.

14th January (2)

A detail of a picture taken in 1967 in the Vox Works, Erith. The AC30 in view is a Top Boost model with large main coupling caps (Dubilier) and an array of smaller dark- and light-coloured signal caps. The dark ones are presumably red Lemcos, the lighter ones Dubiliers, as used in the fully solid state amps and late-run AC50s produced by JMI.

On the centre handle an inspection tag, and in the bottom of the box the guarantee documents in a brown envelope.

In 1967, wooden cases for the solid state range were supplied in "undressed" form by the cabinet makers Heslop and Gla-Rev - in other words, no vinyl, no grille cloth, no holes for handles, and so on, just the plain case. Covering and fitting out was done by JMI staff at the Erith Works. This is likely also to have been the case for AC30s.

Serial number 22177.

13th January (2)

One of the fonts used for copper panels in 1963 (letters and numbers) is "Futura Bold", as supplied at least by Letraset (which came into being in late 1959). The company's dry transfers will have been used for much design and layout work. As well as producing letters and numbers, Letraset also supplied lines, circles, and so on - graphics of all sorts for layouts.

Below, specimens of "Futura Bold" from the catalogue of 1966. The font was part of the range introduced in 1961:

Catalogue, 1966.

Letraset advert, 1961

13th January

AC30 serial number 17758 from the last quarter of 1964. The original EL84s that came with the amp have date code "B3J1" = 1st week of October 1963; two of the ECC83s, date code "B3E1" = 1st week of May 1963; and the GZ34 rectifier valve, "B2K3" = 3rd week of November 1962. Thanks to Rolf for pictures and info.

The voltage selector is of a type used for only a short time, also on certain AC10s and AC50s - new-style dome case, but a slot on top (presumably so a penny could be used to help turn it).

11th January

Some notes on the "etch and fill" process used to create JMI grey panels in the period 1964-1968, and around 100 black panels for AC80/100s in late 1964 and early 1965.

In very broad outline: - (1) an even layer of brass was applied to the surface of the aluminium; (2) legends and lines were screened on in an ink resistant to acid; (3) acid was applied to the top of the plate - this etched into unprotected areas of the brass, leaving legends and lines standing proud; (4) legends and lines were coloured in silver; (5) blue / grey enamel (black acrylic in the case of AC80/100 panels) was run into the sunken areas of the brass.

Aspects of the process can be seen best perhaps in AC50 panels. For some reason the silver colour applied to the legends of these panels was not all that resilient. Below, an example (one of a number) from which almost all the silver has gone, leaving the raised brass legends and designs.

Panel from an AC50 with a serial number in the 3000s. All silver has worn away, exposing the underlying brass. The brass is also revealed by the scratches in and wear on the coloured infill. Legends and lines stand slightly proud of the colour.

A detail of the black panel of AC80/100 serial number 241. Note how the silver has clogged some of the bowls and openings in the letter forms.

As mentioned at the foot of this page, JMI commissioned "etch and fill" panels, though probably in quite small numbers, as early as mid 1962.

10th January

Recently sold by "Howl Guitars" in Tokyo, an early Super Twin amplifier section, beige cloth, early 1962. The amplifier chassis, made by Westrex, has Haddon transformers, the earliest type of copper panel, white EL84 sockets, and the phantom cut-out for the rectifier valve. The serial number plate, with its three long panels and peculiar attempt at hand stamping, a later addition to this amp.

9th January (2)

The "AC30 Lightweight", not really an AC30 at all, but a solid state T60 amplifier section and supplementary solid state vibrato unit in a 3x10" cabinet. On the plate the model is given as "A.C.30. L". The serial number is part of the sequence of T60 amps.

The AC30 Lightweight ("Transistor Lightweight Thirty") in the JMI Dealer Catalogue of 1964.

9th January

A page on control panels has been set in motion here. Notes on manufacturing processes will follow soon, probably on a page of their own.

8th January

An AC30 with integrated top boost in its copper panel has an Albion output transformer with a stamped date - 14th October 1963. The amp is currently in Japan and registered at the foot of this page.

Albion transformers tend to have dark-coloured varnished paper coverings over their windings (as above), at least from mid 1962. Haddons generally have relatively loose-woven cloth, lightly varnished. Woden transformers have yellow waxed paper tape.

6th January

Further fairly random notes on panels. These will be gathered together more coherently on a page of their own. Most standard black and gold panels on JMI amps (AC10s, AC15s and AC30s), c. 1960 to 1961, were laid out with the same font. The font was used for copper panels, as mentioned below, through to early 1963, at which point a new style of "typography" was introduced.

Specialist panel makers made the majority of panels for JMI. A few, however, were produced in-house - silk-screened and painted.

Note the flaking of the paint. Thanks to Glen for the picture.

The process of producing anodised panels was a complex one. Effectively the steps were: (1) preparing the artwork; (2) setting it up as a silk screen mask; (3) silk screening the bare aluminium with the design in an "ink" that was resistant to acid; (4) immersion of the panels in the anodising acid bath (electricity applied to the bath); (5) rinsing with water; (6) immersion in the dye colour; (7) boiling in de-ionised water; (8) the cleaning away of any ink that remained over the legends to leave the bare untreated aluminium.

Steps (1), (2) and (3) have several sub-steps. Perhaps the most difficult thing, from the point of view of layout, was the "JMI" logo. Black and gold panels have further steps, a second anodisation process to add gold to the legends and lines.

Grey panels were made by a different process - "etch and fill". Details in the design were fairly consistent from 1964-1967. However, early on there may have been at least one variant:

The panel on an early grey panel AC30T. Notice the smallness of the "JMI" logo on the large plain metal background, and the lack of "MAINS", "WARNING" and "SELECTOR". Possibly a repro? It looks to have been made by an anodising process rather than etch and fill. No other example has yet come to light.

Super Twin serial number 2739, an AC30TB (top boost integrated in panel), mid to late 1964. The standard form of the JMI logo on grey panel amps.

Super Twin serial number 5438, an AC30TB, c. 1967. The "JMI" logo is on three discrete parallelograms. They have no contact with the bounding lines. In effect, a return to the format of the copper panels.

Grey panels invariably have "FUSE" rather than "3 AMP.". Occasionally wear brings the brass sub-layer of the "etch and fill" process to the surface. Thanks to Glen Lambert for all advice on the design and manufacture of anodised panels.

5th January (2)

Details from the shots in the previous entry, approximately to scale. The letters on the black panel are slightly more dispersed:

5th January

For comparison, a detail of a "standard" Pre-LOC AC30/6 black panel (early 1961) against an early copper panel (early 1962). The fonts appear to be the same. Note the flat-headed "3" and the "1" with pronounced downward tick. The "JMI" blocks look to be the same too, though the letters on the copper panel may be slightly elongated. There are differences though in the spacing of the letters in at least one of the legends - "MAINS".

Serial number unknown.

Serial number 5002.

4th January

Picking up from yesterday, a copper panel from an amp not too far removed in terms of date from serial number 6822. The three silver parallelograms on which "JMI" sits are narrower and a little more angular; the gap between the JMI logo and "PRODUCT" has been reduced. Letters and numbers are generally spaced further apart. Evidently a third template (at least) by 1963.

Serial number 6822.

Serial number in the low 7000s (?).

3rd January (2)

A small work in progress on copper panels. In 1963 the design changes. Early on the text of the legends is relatively fat; "PRODUCT" lies mid-way between the JMI logo and the silver line; "JMI" is in slightly finer letters.

From some point in the 6000s, the legends are given in taller, thinner type; "PRODUCT" lies closer to the silver bounding line; "JMI" is heavier.

Serial number 6038 appears at present to be the earliest AC30 with one of these revised panels.

Serial number 5002.

Serial number 6822.

3rd January

Further pages from the Vox (Rose-Morris) catalogue - the various formats of AC30 (solid state and valve), along with the AC50 and colossally heavy AC120 combo.

Page 3 of the catalogue, continued below (page 4), and detail.

Detail of the schema of the control panels of the valve AC30s.

The "Electronics and Music Maker" magazine review of the Rose-Morris AC30, December 1981, can be found here.

2nd January

The Vox catalogue of 1981, containing pictures of the factory at Shoeburyness (the old Hayter drum factory). At the time Vox was owned by Rose Morris, having been purchased from CBS-Arbiter. On the front cover, a great shot of AC30 chassis at different stages of completeness on racks. "The Vox Story", ed. Denney and Petersen, has further shots of the assembly process.

1st January

A Happy New Year! Just to signal that a page has been started on the early Jennings companies, correcting some of the things that have been ventured in various printed sources and on this updates page. "Jennings Musical Industries Limited" came into being in the summer of 1956. The first ad. for the new company appeared in "Melody Maker" on 23rd June.

"Jennings Musical Instruments Limited", Tom's first company, ran from 1949 to 1968. The two others had shorter spans. "The Jennings Organ Company Limited" came into being around 1952, and "The Jennings Accordion Company Limited" around 1955. Both had disappeared by the time Tom sold a controlling interest in Jennings to The Royston Group of Companies - late 1962, not late 1963 or 1964, as one sometimes reads. The selling of the stock to Royston is recorded (having already taken place) in "The Guardian" newspaper in January 1963.

Further material will be added to the page shortly, a related page on Jennings Organs to follow.

""Melody Maker" magazine, 23rd June, 1956, along with the accordion version, "Accordion Times", July 1956. Note in both instances the signalling of "Trade Mark".

Updates for December 2020 are now on this page.

Updates for October and November 2020.

Updates for August and September 2020.

Updates for July 2020.

Updates for June 2020e.

Updates for May 2020.

Updates for April 2020.

Updates January, February, and March 2020.