Vox AC80/100 (early AC100) serial number 173


April to August 2023

24th August

The new page on "Musicland", the Jennings shop in Bexleyheath . Further material as ever to be added shortly.

15th August

A page coming soon on "Musicland", the Jennings shop in Bexleyheath. Below, entries for the shop in the "Music Trade Directory and Guide" for 1966/1967 and 1968/1969. In 1966 the shop was still run by Paul Jennings, Tom's son. The letter designations in the entry - "M", "OR", and so on - indicate that "Musicland" sold a broad range of instruments, organs, orchestrations (sheet music), electrical goods, records, PA equipment, and undertook repairs.

Entry for the 1966/67 volume supplied by Jennings to the editors of the Directory by April 1966.

In the edition issued for 1968/1969 things had changed. William (Bill) Doe was in charge, and the range of goods less extensive - a broad range of instruments, electronic organs, and PA Equipment. No more records, sheet music, and electrical goods.

Bill Doe had been manager of the Jennings shop on Charing Cross Road (from some point in 1965 through to January 1967) - effectively Reg Clark's successor. When Tom decided to sell number 100 to the Macaris, Bill was transferred to "Musicland", along with Charlie Cobbett, who had been Artists' Liaison Officer up to that point. Charlie did the repairs of guitars and amplifiers at "Musicland". Paul Jennings stepped back from front-line JMI activities.

Syd Wedeles, who had looked after the repairs of equipment brought into the Charing Cross Road shop (from 1965-1967), left and set up in business for himself (having bought a huge number of components and spares from JMI).

It is not clear at present what prompted Tom to sell 100 Charing Cross Road - possibly a need to cut costs. The decline in profitability of Royston Industries, the company that owned JMI, had already been signalled publicly in late 1966. See the entry below for 2nd August. More to follow soon.

Entry for the 1968/69 volume supplied by Jennings to the editors of the Directory by April 1968. At the end of April 1968 JMI ceased trading.

12th August

Thanks to Martin, pictures of a late grey panel AC80/100, serial number in the 400s, mid 1965, have been . The amp was owned by Robert Valentine, who worked for JMI from 1959 to 1964, and repaired by Alan Pyne, also of JMI (c. 1959 to 1968). The greatest number of AC80/100s in 1965 (serial numbers in the 300s and 400s) went for export - principally to the USA and Europe - but some were evidently retained for the home market (as one would expect).

2nd August

Pictures of a Midas Flight Data Recorder from a sobering and often moving BBC film on the Stockport air disaster of June 1967.

The commercial failure of the Midas recorder was of course the thing that ultimately brought Royston Industries to its knees in 1967, along with Burndept Electronics (which had developed the device for Royston), JMI and a number of other members of the "Royston Group of Companies". Royston had taken a controlling interest in Burndept in 1960 and in JMI in early 1963. Development of such a device was naturally a perfectly reasonable and even virtuous thing, but business analysts had long questioned the wisdom of ploughing the Group's profits into it, especially in the face of stiff competition in the field from Decca and others.

The main type of Midas recorder is pictured below. A second smaller type was produced as a plug-in module for the aircraft's cockpit.

An engineer and analyst at the "Royston Instruments" head office in Byfleet.

29th July

Thanks to Arthur, a batch of insulated standoffs of the type used by Triumph in the assembly of MC100/6 amps; certain AC4s and late AC100s, and in the 7-series.

The standoffs are 7/8" tall and require a 5/32" hole. In certain cases, Triumph looks also to have used ones with slightly longer shafts - probably 1".

26th July

The right hand side of the preamp assembly showing the impedance matching transformers, the ECC83 valves in their cans; and the fixing screws for the boards underchassis. Typical of Triumph practice, the insulated chassis pass-throughs - effectively junction solder points taking signals or voltages from one level to another.

The preamp circuit in overall electronic "form" is similar to that of the MC100/4, though there are naturally significant differences in places - some of great interest. More to come on these soon.

Detail of the early Vox MC100/6.

25th July

A detail of the preamp underchassis of the early MC100/6 - boards for the first gain stage of the five microphone channels (an ECC83 valve for each) and associated impedance matching transformers.

Detail of the early Vox MC100/6.

24th July

A detail of the power section of the early MC100/6. The Radiospares capacitors have the date code "PWC" = March 1965. The phase inverter and driver valves are an ECC83 and an ECC82. In front of those, the B9A and octal sockets for the connectors to the preamp. Left at back, the mains transformer. The potentiometers one above the other are for adjusting the bias of the EL34 valves.

Detail of the early Vox MC100/6.

23rd July

The transformers of the early Vox MC100/6 are colossal. Their dimensions are (lamination stacks only, not including the frames): output transformer, pictured below: 5 5/16" (tall) x 4 1/2" (wide) x 2 1/8" (deep); and the mains transformer: 5" (tall) x 4 3/8" (wide) x 2 15/16" (deep).

The part number of the output transformer is recorded on its paper label as "D55 0/1", perhaps an early "Drake Transformers Limited" code. In terms of physical size, output and mains are considerably larger than those that went into the MC100/4, even though the power section circuits are much the same.

Pictures of the surviving early MC100/6 .

Output transformer of the early Vox MC100/6.

14th July

A detail of one of the two flat-fronted MC100/4s from 1965 currently known. The screws fixing the preamp and power amp assemblies to the box are mushroom head 2BA, 3/8" long - just long enough to fix securely into the cage nuts in the frame of the box and no more. Mushroom head 2BA x 3/8" were also used on the slope-fronted metal-clad amplifiers, and on the MC50/6 and MC100/6. The early MC100/6 pictured in previous entries retains one original.

These screws are fairly scarce these days. Supplies do seem to be held though by a number of companies that deal in hardware for classic cars.

The panels of later MC50/4s and MC100s were fixed in with mushroom head 4BA screws, also 3/8" long.

The amp retains two of its original panel fixing screws.

10th July

The preamp assembly of the first generation MC100/6, arranged on three "decks" - underchassis, plinth, and shelf. The circuit is relative straightforward, but the wiring between levels is fearsomely complex. Prototyping must have taken weeks.

Unlike later MC100/6s the preamp is all valve. Development/design of a transistor preamp for the model must have been underway however when this unit was being made. The MC100/6 mark 2 was presented at the Russell Hotel Trade Fair of August 1965.

Underchassis: Circuits to drive the ECC83s and microphone transformers (one of each per channel).

Plinth: ECC83s; microphone transformers; and linking circuitry for the volume controls.

Shelf: ECC83 to drive the main volume and tone circuits; input and output lines to the power section via a noval socket. An octal socket brings HT and heater voltages to the valves.

9th July

Thanks to Steve, some pics of a first generation Vox MC100/6 assembled for JMI by Triumph Electronics in mid 1965 - the lone survivor from a set of four ordered by a TV Studio in the UK for its live shows. For the time being, a general view of front and power section, the format of the latter much as those of the MC100/6s of 1966 and 1967.

Component date codes: Mullard caps: "A5N" = first quarter of 1965; Hunts caps: "WWS" 11th week of '65.

The power section of a MC100/6 from early 1967. In relation to the earlier amp a few differences of construction and one or two necessary changes to the circuit, otherwise identical.

1st July

On the side panel of the power section (chassis) of a flat-fronted MC100/4 from mid 1965, the initials "SR" = Steve Rolfe. Steve worked at Triumph Electronics, which made the PA amps under contract for JMI, as wirer and amp tester - certainly from 1964 and through into 1966.

MC100/4 (all valve) from mid 1965.

Below, his initials slightly more carefully done on the chassis of AC50 serial number 1749 from the last third of 1964.

AC50 serial number 1749.

27th June

It is clear from the advert below, that JMI's association with Reslo began in late 1960 (and not in 1961 as noted in the entry for 16th June further down this page). Searches through the archival material assembled here have so far not revealed anything earlier than November.

"Melody Maker" magazine, 19th November, 1960.

24th June

A further item offered by JMI in the second half of 1964 as part of its line of portable/small-scale PA equipment: the TOA RA-10 receiver-amplifier.

Detail from the JMI pricelist, late 1964.

A TOA RA-10 produced for the European or American market.

23rd June

Below a CA712 manufactured by the TOA Corporation of Japan. These were supplied to Jennings (for re-sale) in the second half of 1964 by "Eagle International", which was based in Bloomsbury, London. "CA" stands for "Car Amplifier", the idea being that one could drive to an event and hook up the amplifier and its PA horns or speakers to the battery of any car or van.

Detail from the JMI pricelist for portable PA equipment, late 1964.

A TOA CA712 produced for the Japanese market.

20th June

A second side-note on microphones - the JMI piano pick-up (1962 - 1967), generally listed with guitar pick-ups in Jennings pricelists:

Detail from a JMI catalogue of early 1963.

A surviving unit from 1964/1965 (ish). Earlier.

18th June

A correction to the entry for the 16th below. The two "own-brand" mics in the "Precision in Sound" catalogue were made for JMI by Grampian not by Reslo. The "Vox Dynamic Stick Types" is a Grampian DP4. These were available in a variety of impedances. The model name and number of the "Vox Ball Microphone" is not known at present.

September 1964.

It should be said that most of the mics illustrated in September 1964 were also presented in the JMI dealer catalogue compiled earlier in the year. See . Tom's plan from the outset was evidently to offer PA equipment as a range - amplifiers, speaker cabinets, and microphones to accompany.

18th June

The first of two short notes on microphones stocked by Jennings in early days.


Between 1950 and 1963 Tom stocked three main types: (i) made by "Westbourne Sound Equipment" - 1950 to 1957; (ii) of unknown manufacture, possibly Jennings's own - 1957 to 1959; and (iii) a long resonant unit made by Microfisa - 1959 to 1963.

The mics were sold through the Jennings shop at 100 Charing Cross Road and at Trade Fairs. An overview of the fairs attended by Jennings in the 1950s .

July 1950.

January 1958.

April 1960.

16th June

The "Precision in Sound" newspaper-format catalogue of September 1964 - the expansion of the Vox PA and microphone range. As noted in a previous entry Tom had set up a new company - "Vox Sound Equipment Limited" - earlier in the month to handle such things.

The models listed in September 1964 were models manufactured by Reslo, Kent, and Shure, the association with Reslo going back to late 1960 (not 1961 as stated here previously) and with Shure to 1962. Kent was new for JMI in 1964. The "Vox Dynamic" and "Vox Ball" models were made for JMI by Grampian (not Reslo as previously stated). Jennings did not at any point produce or assemble its own microphones.

Below, the representation of the Reslo mic illustrated in the entry for 2nd June lower down this page. Note the "VOX" legend on the throat of the mic. Whether this was the designer's fancy is not known. There is certainly no sign of a logo on the boxed example.

Earlier Reslo mics packaged for JMI normally had a cursive VOX logo either on an aluminium "collar band" or on a disc inset into the body of the mic.

14th June

AC100 serial number 1944, chassis produced by Triumph Electronics under contract for JMI. Further pictures . The grille cloth was evidently replaced some time ago. General condition of the amp and cabinet is good. The paired-up filter capacitors on the upper chassis are a later adjustment, two new cans added to the existing two (in line with OS/167). The back panel has square rather than rounded corners.

12th June

Alan Pyne's service sticker in a late AC80/100 he repaired for Bob Valentine, also formerly of JMI. Alan took over 119 Dartford Road when Tom's company, "Jennings Electronic Industries", folded in 1975. Further pics of the amp to follow, thanks to Martin. A page on Alan can be found on the .

The amp serviced on the 6th August 1979.

2nd June

Some updates and new pages (on Vox PA equipment and microphones) coming shortly. Below, a Vox Reslo microphone with its original box and fold-out leaflet, sold by JMI in 1965.

11th May

An update to the new page linked in yesterday's entry. The trade show attended by JMI in 1961 (referenced at the foot of the page) was not one that was part of an event staged by "Banjo, Mandolin and Guitar" magazine, but rather the "Fretted Instrument Guild". 1961 was the Guild's 8th "Guitar Festival". It is not known at present whether JMI attended the 6th and 7th Festivals, respectively 14th April 1959, and 6th April 1960, both at St Pancras Town Hall, London.

Trade Shows were held in a hall subsiduary to the main hall in which the Festival (competitions, demonstrations, and so on) was held.

10th May

A page on early Jennings stands at trade fairs has . There is still a good deal of documentary material to add, so it may be that further pages will be needed in due course. Additions/changes will be signalled as they are made.

The earliest known picture (at present) of a Jennings stand - "National Accordion Day", Central Hall, Westminster, November 1950.

2nd May

Recently come to light in Spain, AC100 serial number 1944, chassis assembled by Triumph Electronics for JMI, probably early 1967, no component date codes immediately visible. At some point the amp was turned into an AC100/4 (circuit diagram OS/167) - two further filter capacitors added. It is not clear whether the phase splitter is an ECC82 (OS/036 - standard Mark 2 circuit) or an ECC83 (OS/167). Pictures to follow.

16th April

December 1953, a first report of the acquisition by Tom of 115 Dartford Road - "Unity Works" (or "Unity House") as it came to be called a month or two later. With the new space came the expansion of the "Jennings Organ Company" - the production of console organs and further models of Univox. More to follow.

December 1953. The magazine from which this piece came - a review of activities in the accordion and music world generally (with many good adverts) - is extremely scarce these days. The set to hand came from a seller in Turkey.