VOX AC100 - UPDATES AND NEW INFO
April and May 2024
30th May
The entry for AC100 serial number 1115 has been expanded with new pictures and info. The significant gap in the sequence between 1115 and 1153 may be a result of the fire at the West Street Works in Erith in early December 1965.
From a report of the fire in the local Dartford press, December 1965. The mention of "Beatles type amplifiers" by Reg Clark, JMI's General Sales Manager, means AC100s.
Following the fire, production was started again fairly swiftly in a building nearby made available to JMI by Burndept Electronics, which owned the West Street Works and had rented it (in part) to JMI from mid 1964.
29th May
For the time being, just to note the existence of two more AC100s - serial numbers 824 (in France) and 1275 (in the USA), no further comment, especially in relation to the latter.
28th May
Further pictures of AC100 serial number 448, the latest cathode biased amp known at present have now been added here. Produced for export to the USA, summer or late summer 1965.
27th May
A series of updates to the main AC100 pages are currently in progress. Some new pictures of serial number 323, late Spring 1965, have recently been added here.
24th May
In relation to the development of the Vox Radio Microphone system, a page from an early draft for the General Post Office's (G.P.O.) Radio Microphone licence in the National Archive. The licence at this time was evidently being worked up from an existing licence for induction loop systems (as installed in cinemas and theatres).
The principal G.P.O. departments involved in the drafting process were - Engineering, Solicitors, and Radio Services, in particular the VHF Division. Other departments suggested changes and improvements.
In late October 1962, a memo noted that the some speed was necessary in formulating the licencing scheme as "at least two manufacturers have developed equipment which may soon pass our type tests and there is a known demand awaiting this development". One of these manufacturers was certainly Lustraphone. The other may have been Jennings, which had recently demonstrated its system at the Russell Hotel Trade Fair.
More to follow soon.
Draft radio microphone licence in early 1962.
Detail of the first lines.
13th May
As mentioned on the recent page on Vox microphones, the "Precision in Sound" newspaper-format catalogue, issued in the late autumn of 1964 illustrates a good number of the mics offered by JMI at the time.
"Precision in Sound" newspaper-format catalogue, autumn 1964.
Microphones bought in from "Kent", which was based in the USA, form around half the roster represented. The models, most described as being "non-directional" (= "omni directional"), are:
D.M.7 Dynamic, desktop or floor stand.
D.M.10 Dynamic, desktop or floor stand.
D.M.13 Dynamic, hand use or floor stand.
D.M.17 Dynamic, cradle mounted.
M.18 Crystal, desktop or floor stand.
D.M.20 Dynamic, recording or PA.
D.M.21 Dynamic, hand use or desktop.
M.23 Crystal, desktop or floor stand.
D.M.47 Dynamic, studio or outdoor use.
M.120 Crystal, floor stand.
M.135 Crystal, with built-in volume control.
These were all Japanese-made and sold in Japan principally by Aiwa. In the USA they were distributed, with new badges and logos, by "Kent" and "Calrad" (California Radio). JMI's deal with "Kent" also encompassed drum heads, drums being the company's main business.
Below, the entry in the catalogue for the D.M.18 and an Aiwa D.M.18 long in the UK:
Kent D.M.18.
Aiwa D.M.18.
10th May
Thanks to Martin, a picture of a superb Vox Radio Microphone set, probably early 1965.
9th May
Further pictures - some great details - of the Jennings R.L.S.5 column can now be found on this page.
6th May
Thanks to Bernhard, pictures of a Jennings R.L.S.5 column - a Rotating Line Source speaker unit containing five speakers, one in the base pointing upwards, four rotating on a central shaft. Few of these units survive. Further pictures will be set up on a page of their own.
Jennings R.L.S. 5 rotating speaker column.
29th April (2)
An ancillary page coming soon on Vox microphone stands. In the main these were made by Reslo (from 1961 through to 1968) but branded for JMI, much as the microphones, with "VOX" in cursive script in enamel roundels, black initially, then red.
From late 1964, Tom set in motion a new drive to sell complete Public Address "sets" - amplifiers and speakers along with mics, stands, cables, all that was required for the installation, whether permanent or temporary (set up, pack, stow or move).
The PA "industry", such as it was, seems to have been a little bit wary, even dismissive of Jennings's efforts, but the equipment produced and sold by JMI was extremely good.
29th April
Just to record some updates to the new page on Vox Radio Microphones - (1) a note on the two classes of GPO licence, one for "Public Address", the other for "Film and Stage" - JMI will probably have had both; (2) addition of an advert for the new Reslo radio mic (mid 1965); some further details on the redesign of the unit (as illustrated in the pic below), which was well underway by August 1964, when the radio mic was shown at the Russell Hotel Trade Fair.
Trade magazine, January 1965, the design of the unit a significant departure from initial form (as illustrated in yesterday's entry).
28th April
A new page on Vox Radio Microphones, 1961-1966, has been started, further material as ever to be incorporated soon.
Detail from the JMI dealer's catalogue of 1964.
26th April
A new page on Vox microphones, 1960-1968, has been started, further material to be incorporated soon.
25th April
Pictures of AC100 serial number 398 have been added here - standard date codes on components - final assembly mid 1965.
24th April
A detail from a photo of the back of George Harrison's SDL cab, December 1964. Note the broken Kenrick Shepherd ball castor in the back. This evidently failed shortly before the concert at Cincinnati on August 27th. The tour had begun on the 18th. Later all the castors on both SDLs were removed.
Broken Shepherd's castor at left.
Cincinnati, 27th August, 1964, a block of wood standing in for the castor.
One can tell from the neck of the castor (distinctive form) that the ball/wheel was of 2" diameter. The stem (broken off in the pic) is likely to have had a screw thread. Two slightly later basket-top trolleys certainly do - 5/16", British Standard Whitworth (BSW). Kenrick Shepherd castors of this type are scarce these days. By far the most common are those with flat fixing plates or smooth unthreaded stems. Neither types fit (or are appropriate for) JMI AC100 SDL trolleys. The larger Shepherd's castors - 2 1/2" diameter balls/wheels - have much larger threads, which again, do not fit JMI AC100 SDL trolleys.
12th April
A shot of the preamp of AC100 serial number 225 from Jim Elyea's book. There are two things of note: (1) the grey 0.05mfd Radiospares "snubber" capacitor over the mains switch. These were fitted at factory to many AC100s and AC50s produced with a view to export to the USA. The option of the cap. was never registered in circuit diagrams.
(2) the English-made Daly capacitor at the right-hand end of the tagboard has the date code "WE" = May 1965. Perhaps one of the spare/replacement components supplied to Thomas Organ by JMI?
That the amp was in California by April '65 seems clear: a photo of it appears in the first issue of Thomas Organ's "Teen Beat" magazine, printed while Marv Kaiser's first Vox "Battle of the Bands" competition was still in progress (see the page linked above).
AC100 serial number 225.
Detail. "WE" is May 1965. Solder joints look old.
Whether serial number 225 travelled with number 226 is unknown: but the latter was certainly produced for use in the USA too.
Detail of serial number 226, the 0.05mfd Radiospares cap visible top right.
AC100 serial number 392, also fitted at factory with the 0.05mfd Radiospares snubber.
8th April
Below, the wiring schema of the upper compartment of the AC100 SDL speaker cabinet (with basket top trolley) from early 1965. Total impedance 15/16 ohms. The lower compartment is arranged similarly. The two were wired in parallel at the input socket, resulting in a total impedance of 8 ohms for the cabinet as a whole.
Wiring schema of the upper compartment of the AC100 SDL speaker cabinet (with basket-top trolley) from early 1965, date codes on the speakers mid December 1964.
Each compartment has a pair of 1uf capacitors, wired in parallel for a total of 2uf - to protect the Goodmans Midax horns from potentially damaging low frequencies.
Detail of the upper compartment of the SDL cab, early 1965.
The wiring scheme adopted for this cab (and at least one other) was actually the second adopted by JMI. The first scheme, used in the first five (certainly) or six cabs, is entirely different, the two pairs of capacitors being mounted together in the lower compartment. Below, a detail from a photo of one of the cabs issued to the The Beatles in mid August 1964.
Detail from a photo of one the SDL cabs issued to the Beatles.
Four of the five cabinets that have this first wiring scheme were made together: two for the Beatles; and two for loans and demonstrations. These last were lent out by JMI for short stints to various bands for key performances, live and filmed, and exhibited at trade fairs and other events. Reg Clark, JMI's General Sales Manager, is seen with one, for instance, at the Russell Hotel Fair, late August (ie. while the Beatles were away in America).
A fifth was made a little later - at some point in November. This went out on loan in the UK in December, and was then shipped to the USA, also to serve as a loans and demonstrations unit - see this page.
7th April
A rudimentary schema of an AC100 on top of a trolley with parallel bars (as from above). The position of the amp's feet are marked in red. As can be seen they straddle the trolley rather than slotting in between front and rear bars, which in many respects would be a more logical arrangement.
That an amp might accidentally be tugged backwards would probably be an extremely rare occurence though. Most of the weight of the amp (the transformers) in any case is towards the front.
The schema represented is based on AC100 SDL serial number 392. The amplifier section cabinets of serial numbers 262, 328, and 337 have feet in identical positions.
Not to scale. Based on AC100 SDL serial number 392. The (tubular) bars of the trolley are 7/8" in diameter. Note that the feet, which are shallow, locate against the curve of the bars. The width given for the centre section of the trolley top - 16 1/2" - is the total distance from outermost edge of one tube to the other.
Detail of AC100 SDL serial number 392, mid 1965 (speakers dated May '65), parallel bars across the top of the trolley.
6th April
Further slightly random notes on early AC100 SDL speaker cabinets and trolleys.
(i) Early speaker cabs (late 1964 and early 1965) were of the same size as later ones (mid 1965 to 1968): 40" tall; 11 1/2" deep; and between 27" and 27 1/4" wide.
(ii) The distance from outer edge to outer edge of the parallel bars immediately below and above the handwheel of early basket-top trolleys is 6 3/4". Later trolleys: 9".
Side bars of one of the second generation basket-top trolleys, the cab tilting back (so piping sloping).
(iii) The AC100 amplifier sections that were sent out with AC100 SDL speaker cabs normally (as a matter of course) had black cloth. Very few amps in thin-edged boxes were done out in black.
(iv) AC100 amplifier sections were regularly fitted with feet (small furniture glides) that do fit as logically as one might expect on trolley tops. More to follow on this. Below, a picture of the AC100 used by Lennon, Belfast, 2nd November, 1964. The amplifier section was not the one he normally had. Its feet (furniture glides) do not slot properly into the basket top.
Belfast, 2nd Nov., 1964, the feet on the right-hand side amp sit on the bars, not inside the basket top. The amp was probably a spare, less likely borrowed from one of the other bands on the package tour.
Serial number 178 is similarly lop-sided when placed on top of a basket trolley: the only way to position the amp is with two feet within the top, the other two sitting on the bar.
5th April
As mentioned yesterday, AC100 SDL serial number 236 (black panel, cathode biased) is the earliest surviving instance currently known of a trolley with parallel bars on top - in other words a standard "Mark 2" trolley. That the speaker cabinet is an early one is clear from the position of the XLR socket, the wiring evidently feeding to it from the upper compartment of the cabinet. A little later on, the wiring pattern of the SDL cabs was changed, the XLR socket repositioned lower down the middle back board so the wires could feed to it from the lower compartment.
AC100 SDL serial number 236. XLR socket relatively high up on the back board, indicating that the wiring to it issues from the upper compartment of the cabinet. The original speakers have unfortunately gone, but the original wiring loom is evidently still in place.
It is likely that most of the SDL cabs that were sold with black panel AC100s had cabs of the type illustrated above.
Below, a slightly later cab in need (as pictured) of some attention. The speakers have been out and put back in rather haphazardly, but key portions of the wiring loom are intact. Note the presence of the green capacitor positioned to the front of the compartment, as in two of the early cabs with basket-top trolleys. In the case of the cab below, however, the wiring that leads to the XLR stems from the lower compartment.
Possibly a replacement trolley from an American Super Beatle - note the castors (of the type normally found on Thomas Organ-made trolleys).
The lower compartment of one of the cabs with a basket-top trolley, early 1965. The wires leading to the XLR socket issue from the upper compartment (just visible at the top of the pic.)
By mid 1965, JMI introduced a further change: instead of the paired green 1uf capacitors, a single larger-bodied 2uf capacitor painted black and positioned further back in the cabinet.
Speaker cabinet of AC100 serial number 392, picture showing the position of the new (relatively) type of 2uf capacitor (made by TCC but painted black by JMI). The speakers in this cabinet have mid May 1965 date codes.
4th April
To return to trolleys: note 4) standard later JMI AC100 SDL trolleys (certainly in production by February 1965).
In contrast to early basket-top trolleys, later "standard" JMI trolleys were made out of 7/8" diameter tubing all round, the frame consisting of three (rather than two) sections that slotted together: the base (with wheels), and two side pieces that contained the locating points for the cabinet swivel mounts and half each of the top. These side pieces slotted into the base and into each other at top.
Early basket-top trolleys came in two sections: the base and a single section comprising of sides and top.
Detail of AC100 SDL serial number 392, mid 1965 (speakers dated May '65), parallel bars across the top of the trolley.
Below, a picture of an American Super Beatle trolley, wheels removed and part dismantled to show the three principal elements. In overall form, these trolleys were copies of JMI's AC100 SDL trolleys, though there are significant differences in detail.
American Super Beatle trolley to show the three main elements. JMI AC100 SDL trolleys had the same tri-partite form, and identical dimensions. Areas of difference: the type of castors used, the swivel mount, the intermediate bars on top; mode of production. The trolley pictured above was flown about the USA in the 1970s by "Consolidated Airlines" (transit labels still sellotaped on upper and lower sections).
The earliest dated instance of a new-style JMI trolley? - February 1965 in a short film clip shot at Dartford Road. The earliest instance currently known in terms of surviving amps? - AC100 serial number 236. More on the early black panel amps tomorrow.
3rd April
Just to record (as material gathers) an analogy for the thickness of the early AC100 trolley side mounts: the Line Source 40 (LS40) public address column tilt-back stands.
Early AC100 SDL side mount, detail showing the thickness of the metal ring into which the mount on the cabinet slots. In between the two, a brown phenolic ring.
One arm of a Line Source 40 tilt-back stand, the cup at the end of similar thickness to the AC100's trolley mount.
Whether other early amplifier trolleys had similarly substantial swivel mounts is not known for certain at present - but the likelihood is strong one. Below, an AC50 trolley (sometimes called a Mark 3) with basket top from early 1965, the diameter of its tubing along the lines of the early AC100 SDLs: lower section 7/8"; upper section 3/4".
These trolleys were supplied with late single-channel diamond-input AC50s and early large box AC50s - from late 1964 into early 1965.
2nd April
A rare instance of a "Jennings Electronic Industries" circuit diagram, the page below part of a set of five for the 100W Public Address amp with reverb. The sheets were drawn by Albert (Bert) Hogben, who had worked for Tom in JMI days.
A xerox made some time ago from a spiral-bound collection. The set is dated 4th December 1973.
1st April
Picking up from yesterday's entry: note 2) The swivel mounting hardware of the early basket-top AC100 SDL trolleys.
Again, the format is different from the one later adopted by JMI for its standard AC100 trolleys. The handwheel face is engraved rather than pressed, the logo defined by bounding lines rather than fully recessed letters. This can also be seen in the photograph submitted by JMI to the Old Patent Office in October 1964.
Handwheel face, basket-top cab.
0Detail from the photo of the AC100 SDL registered by JMI with the Old Patent Office in October 1964. The logo is "blued" out to indicate that the name was not part of the application. "VOX" had already been trademarked by Tom in the 1950s.
0Handwheel inside face.
Forming part of the structure of the trolley frame is a sizeable hoop that locates over the "castle" style cabinet mount. Between the two, a brown phenolic ring (second photo below). The standard later JMI format can be seen on this page.
A circulat metal plate (not shown) goes between the trolley mount and the handwheel.
More to come on the early trolleys in a coming post.