VOX AC100 - UPDATES AND NEW INFO
2026
16th July
Below, one of the picture pages from the JMI 1966 catalogue included in a promotional pack handed out at the Russell Hotel Trade Fair in August 1967. Shots of the pack as a whole can be seen on this page. Although the AC100 was still in production in late 1967, the 1966 catalogue was of course fairly anachronistic in the UK at that point.
But the page in view was anachronistic even in 1966, as the AC100 chassis featured is a "100 Watt Amplifier" from the summer of 1965 - no brimistor, black-shrouded transformers, and heavy passivation (a yellow/gold coloured chemical corrosion protection) for the plinth.
15th July
In relation to the entry for 8th July below, instructions on the rear of a Triumph Silicon 100 amplifier section, identical to the ones on the JEI PA100 Reverb pictured below. They not figure however on any JEI PA100 without reverb that has come to light so far. This is likely to have been Triumph's decision: Triumph assembled the Jennings solid state range for Tom under contract. The lines - done in letraset - are also to be found on the rear panel of Triumph's own-brand PA100, which had the same power section as the Jennings version. Preamps differed though.
More on Triumph to come shortly (including some comments on certain erroneous statements on other websites).
Triumph Silicon 100.
Triumph PA100.
Triumph PA100 rear panel, identical to that of the JEI PA100R, the same layout as the JEI PA100 (but without the text).
13th July
Four pictures initially of AC100 serial number 414. As in the case of all grey panel cathode biased AC100s that have emerged so far, the Woden mains and output transformers have "BW" date codes = February 1965 for their manufacture.
AC100 serial number 414.
11th July
Some pictures coming shortly of AC100 serial number 414, probably ready for sale in later Spring 1965, very few changes.
8th July
Better pictures of the JEI PA50 that turned up recently in Enrope, along with pictures of a JEI PA100 with reverb, very little seen these days. Original production numbers are likely to have been low to start with though.
The instructions relating to power output and impedances on the back panel of the PA100R do not seem to have been added to plain PA100s.
JEI PA50.
JEI PA100 Reverb.
7th July
A detail from a photo of Don Greer with his collection of Vox amps, early 1980s, printed in "The Vox Story", ed. Denney and Petersen, 1993. In view (among other things), an AC100 amplifier section, and an MC100/6 Public Address amp - possibly the one sold in Florida a few years ago.
27th June
Pictures of AC100 serial number 619 have now been added here. The latest visible component date code is on the choke - "EW" = May 1965 for its manufacture, part of sizeable batch made by Woden for JMI.
AC100 serial number 619.
23rd June
Below, a detail from a photo taken in the R&D room at 119 Dartford Road, late 1964. Under one of the benches, assemblies for a species of Public Address amplifier? The shortness of the rear edge of the preamp section at left is suggestive. If the chassis with the huge transformers behind it formed part of the unit, then at least 100 watts must have been in view.
That the two assemblies were part of a console orgam is perhaps possible, but the left-hand section is difficult to "place" in that sort of context.
The main index page for Vox Public Address amplifiers and speakers can be found here.
End on view of a MC100 preamp.
23rd June
Thanks to Marco, some pictures coming shortly of AC100 serial number 619 (00619), a "100W Amplifier", latest visible component code on the Woden choke: "EW" = May 1965 for its manufacture. One of the original yellow-print Mullard ECC82s has "B5E2" = 2nd week of May '65.
20th June
A detail of the logo on the speaker cab. accompanying Paul's first AC80/100, admittedly small, but showing clearly enough the dimpled black rexine on the wood block (certainly not basketweave).
19th June
In contrast to what was said in the previous post, photos taken in the summer of 1964 indicate that the wood block logo on the speaker cabinet that accompanied Paul's first AC80/100 did not have a basketweave vinyl covering. It appears to have been more as the example pictured below - dimpled black rexine. To be illustrated shortly.
17th June
Copied over from the T60 website, the second principal form of T60 speaker cabinet logo, single letters on a wood block covered in rexine, used from later 1963 to the late summer of 1964, though not exclusively. One also finds older-style perspex and early dimpled plastic logos in 1964 too.
Single-letter wood-block logos were also used for the 2 x 15" cabinets issued with early AC80/100s, a prime example being serial number 177, though with basketweave vinyl rather than rexine - on this page.
It is worth saying that since the speaker cabinet issued by JMI with Paul McCartney's first AC80/100 was covered in basketweave vinyl its wood-block logo is likely to have been covered in basketweave too - [19th June: - incorrect, see the post above].
16th June
Coming shortly, full coverage of the Rosetti / Triumph catalogue of the early 1970s: "Amplification, Electronic and Reed Organs, Mikes and Effects by Rosetti".
14th June
A small picture (for the time being) of a JEI PA50, serial number unknown, that turned up in Germany recently. The only other that has surfaced in the last few years is serial number 1043, further below.
As in the case of the amp below, no handle.
JEI PA50 serial number 1043.
5th June
A small detail of an early Metal Clad public address amplifier (sloping front, single metal handle) on stage - probably an MC50 or MC100.
Photo taken in November 1966.
1st June
Recently sold in Europe, a good market for JEI from its inception in 1968 through to the mid 1970s, a handsome pair of LS.412 speakers. For another set, see this page. The drivers are Fane 122/10, cast iron frames, power handling 20W, 8 ohms impedance (marked as such on the factory stickers), and frequency range 30-5000 hertz, so a slightly reduced upper range. Other versions of the 122 reproduced up to 17000 hertz. Most of the speakers in the columns appear to have been stamped "Hi-Fi" with a round ink stamp.
This was set number 339.
22nd May
Some notes on the circuit of the "100W Amplifier" illustrated in the previous two entries:
Main HT (B+) is 479v; on the screens 460v; bias (on the grids) -36v. The original divider/bleeder resistor now measures 15K (should normally be 18K). The voltages on the various nodes in the preamp are marked on the image below:
Detail of the "100W Amplifier" circuit diagram, on which few voltages were noted by JMI. *277v on the cathode of the ECC83 is inferred, not measured.
The numbers given above are probably typical of other "100W Amplifiers" - further details to come - though naturally after 60 years one has to allow for a certain degree of variation.
19th May
The box of the amplifier illustrated in the previous entry. The "V" and "O" are original, the missing "X" now replaced. The feet - still in their original positions - are arranged in such a way as to fit perfectly on the bars of a SDL trolley. Amps issued with 2x15" speaker cabinets generally had feet positioned close to the corners.
The box was one of a good number made for JMI by "Gla-Rev", run by Henry Glass. The baffle is chipboard.
The grille cloth is staying as it is. It would be impossible to remove without breaking the fixing lugs of the original letters.
17th May
Recent pictures of a "100W Amplifier", serial number probably originally in the 600s. The latest dated components are of May 1965. The amp was well used during its time, modified in the 1970s, and put away in a potting shed in the late 1980s / early 1990s. It is still in good working order.
JMI ran the preamp of the "100W Amplifiers" significantly harder than that of the Mark 2s - which is to say the Mark 2 was tamed down. The "100W Amplifiers" have over 100v on the first ECC82 (instead of 80v), and around 270v on the ECC83 (in contrast to the 190v of the Mark 2). They are altogether better sounding than their successor.
15th May
A nice late JMI ten-inch wall speaker - with a Celestion 7721, 15 ohms - that passed by a little while ago. An instance of this type of Celestion (widely used by JMI from 1966) occurs in a slightly later ten-inch wall speaker with a plastic trapezoid logo, "VOX" in silver letters, as on speaker cabinets issued with early solid state amps.
9th May
A quick note on early thick-edged boxes, serial numbers in the range 216 to around 300. These for the most part had a single long cut-out in the baffle. Later, when the grey-panel cathode biased AC80/100s came into production, baffles had two openings, slightly taller than the long slot of the earlier boxes.
The single slot of serial number 226 evident behind the cloth.
The box of the AC80/100 illustrated below, entry for 3rd May, recovered and given repro double-pin corner protectors by the seller.
The box of grey panel AC100 serial number 323. Two openings in the baffle, standard from around this point until end of production.
Below, an early thick-edged box (probably from a black panel AC80/100) sold twice on ebay in different states, an initial renovation and a second.
First appearance.
The same box redone: new grille cloth, logo repositioned, repro single pin corner protectors (instead of the double pin ones above); replacement handle; arrangement of the back board unchanged.
Second appearance. Single long slot in the baffle.
8th May
Old pictures of a "100W Amplifier", serial number originally in the 500s or 600s, exported to the USA by JMI in the last third of 1965. Note the large grey Radiospares capacitor by the mains switch.
3rd May
Below, an AC80/100 sold by a seller in the UK (Thames Valley) over the course of 2009 and 2010 in separate lots: box on its own, chassis (with preamp board and valve sockets), transformers and choke one by one, and so on.
The main items lacking were the control panel, Bulgin fuseholder, and main power section board. The box had been renovated by the seller and a new back board provided.
In view of the green Woden transformers, various component date codes, and the thick-edged box, the amp's serial number will have been in the range 216-230. An entry at the end of the page on later copper panelled AC80/100s to follow.
Pictures taken a few years ago:
Recovered by the seller, who added repro double-pin corner protectors. The box has a ply baffle. Grille cloth replaced.
Chassis originally assembled by Westrex, marked "165", meaning at present unknown. For Westrex markings on AC30s, see the final section on this page on the AC30 website.
Currently the chassis has a grey control from another amp (acquired from a seller in the USA).
28th March
It is something of a truism these days to say that amplifier manufacturers ran valves hard in the 1960s. JMI pushed the EL34s it fitted to its AC50s and AC100s to their limits. Bias was generally set at -34V. Most techs now would now baulk at anything below -40V, certainly for modern production EL34s.
The bias of course regulates the amount of current flowing on the plates. Too little bias and the valves "red plate", shortening their effective lives.
Where AC100s are concerned, four components need to be in good order: the two 330K resistors following the bias network, and the two 0.1uf signal/coupling capacitors (all marked on the sheet below). Should there be a large imbalance in the resistance of the resistors, or leakage in the capacitors, the bias for one or both pairs of EL34s will be thrown off. A leaky capacitor might create a drop of several volts. Erie 330K resistors often slip badly out of tolerance, more so for some reason than most other values. WIMA 0.1uf caps, after 60 years use, are not always to be relied upon.
A detail from the circuit diagram for the "100W Amplifier", -35V before the 330K resistors, an expected (though not stated) -34V on the grids of the valves themselves.
AC50 serial number 1338, early large box, bias noted in pencil "34v", omitting the minus. -34v is the norm. A note of the factory setting also survives on the underchassis of AC50 serial numbers 1411, 1524, 1708, etc. Serial number 1354 appears to have been set at -33V however.
23rd March
Recently posted on the updates page of the Vox AC30 website, a shot of the remaining letters on a Vox AC100 from the late summer of 1965 (circuit conforming to the "100W Amplifier" sheet). The "X" in this instance clearly had two lugs, one top left, one lower right. Other examples of the small single "X" have a single lug at the intersection of the arms, perhaps having been cut away from a small single-piece logo which had lugs only for the "V" and "X".
Single-letter logos are uncommon on AC100s. At present just seven are known, at least two of which will probably not emerge from their hiding place for some time yet (but they are known from photos).
AC100, serial number somewhere in the 600s (plate gone).
The other side of the baffle, the "V" with three lugs, the "O" and the "X" two. Please forgive the rough and ready outlines.
7th March
Just to say in relation to yesterday's entry, the Beatles did not need their amps for appearances scheduled between 18th-21st of November.
6th March
The Glad Rag Ball, 20th November, 1964, Empire Pool Wembley, a detail of an AC80/100 on stage provided by JMI for the event, black cloth (to accompany a SDL speaker cabinet). The amp is the dead split of one issued to the Beatles in late July. Is it the same amp? The arrangement of letters and alignment of the diamonds across the whole of the front look to be a match.
Glad Rag Ball, November 1964.
Stockholm, July 1964.
17th February
"Exchange and Mart" magazine, September 1969, a second-hand Vox MC100/4 public address amp for £70. List price in 1967 was £95. The main index page on JMI's range of PA amps is here.
16th February
"Exchange and Mart" magazine, September 1968, a couple of second-hand AC100s at the opposite ends of the spectrum in terms of price:
A growing collection of small ads relating to AC100s can be found on this page.
4th February
A couple of relatively recent shots of AC100 serial number 2103, - a late amp with main filter capacitors in pairs and other elements as expressed in OS/167 - have been added here.
31st January
The entry on AC100 serial number 660 has now been updated. Further updates across the serial number ranges to come soon.
30th January (2)
Thanks to Laudo, pictures coming soon of a superb "100W Amplifier" - AC100 serial number 660 - from late summer / autumn 1965, electronics immaculate and original.
30th January
Sad remains: tabs (a left-hand set) from a Jennings organ that came up for sale around four years ago. Such tabs were common across the range (from the J68 to the J73). The pages on the various models are gathered together and linked on this index page.
A detail of a J68 from Werner's "Vintage Keys Showroom" - the organ side of Jennings tabs.
29th January
Rod Argent's post Zombies band, featured on the front of the newspaper-format flyers issued by Jennings for two consecutive Russell Hotel Trade Fairs (1969 and 1970). In view, J200 amplifier sections with D4 and B4 speaker cabinets. A photo currently held by Getty Images shows that the band had a colossal amount of Jennings equipment in 1969 / 1970, far more than is shown in the shot below.
Detail from "Jennings News", version issued in the autumn of 1970.
The J200s pictured above are liable to have been early ones. There are no "Jennings" logos lower right on the cases.
J200 serial number 1018, ready for sale in the third or fourth quarter of 1970.
28th January
The later Jennings PA100, purple livery, late 1973: likely to be a Jennings design as a circuit diagram survives, drawn by Bert Hogben, who had worked for Tom in JMI days.
As mentioned a little while ago, versions of the amp were also marketed by Colorsound and Fal. Perhaps some reciprocal agreement?
In one of those high ironies, the reverb pan fitted to the JEI PA100 was a Hammond. In the 1990s Dick Denney reported that JMI - probably meaning Tom - was loth to purchase a license and so had developed its own system (based on phono cartridges).
Hammond reverb tank mounted above other assemblies.
A page from the circuit diagram for the JEI PA100 of 1973.
27th January
Not much seen these days, a JEI "Portable Electronic Organs" folder, the one in view supplied with a Jennings J71 three-manual organ, contents unknown, perhaps analogous to the folders compiled by JMI for the Super Continental (circuit diagrams, notes on operation, and so on).
26th January (2)
An interesting feature of the JEI PA50 mentioned below (23rd Jan.): the provision of microphone transformers (sometimes called "matching" or "input" transformers) for three of the four inputs - from front, left to right, numbers 2-4. These have all the appearance of being original. So far no JEI PA100 fitted out in this way has come to light.
PA50 serial number 1043, upper chassis.
PA100 serial number 1045, upper chassis.
26th January
Just to note that the pages on the Jennings J70, J71, J72 and J73 organs have recently been updated - see the main index page here. Further details to be added in due course.
One of the more unusual things about the two-manual J72 console organ (effectively a J70 in a two-section case) was that it was described by reviewers as being new both in August 1971 and August 1972 (Russell Hotel Trade Fairs).
Details from the Jennings brochure produced to accompany the company's display the Russell Hotel Trade Fair of August 1972.
25th January
An early Jennings J40 amplifier on sale in California - thanks to Dave M. for indicating the existence of the listing, some time ago now.
The page on the J40 can be found here.
Early Jennings J40, serial number unknown.
24th January
The page on the Jennings AC40 has now been updated. Below, a detail of the chassis of one of the amps with drawbars, holes drilled for potentiometers. AC40s with drawbars naturally had their own type of control panel. It is likely that from some point in 1971 all chassis were drilled to allow for the use of pots. By August drawbars had become an option rather than standard.
23rd January
Offered by Jennings from early 1968 a little way into 1973, a PA50, extremely scarce these days. The one pictured passed by around three years ago. Catalogue images tend to show the model with the opening for the Reverb control blanked off, as in the case of the amp below. Whether any actually were produced with Reverb is unknown at the moment. If so, doubtless very very few. Nothing is said explicity of the availability of the effect in the surviving publicity material.
Back panel much as the B50 and O50.
22nd January
February 1970, review of the Jennings display at the Frankfurt Music Fair in an international music trade journal, the Attack Percussion unit and Scrambler pedal picked out for a small photo feature.
February 1970.
"Exchange and Mart", June 1970, a great pitch for the unit.
21st January (2)
Thanks to Martin: Dartford Road, the loading of a lorry bound for Wupperthal, "Jennings Electronic Industries" days, c. 1971. Inside at left, Jack Jennings, Tom's brother. As at JMI, Jack not only oversaw packing and despatch, but the stamping of serial number plates (and the keeping of records thereof). The consignment in view was evidently sizeable.
21st January
A shot of one of two Jennings AC40s with red drawbar ends that came up for sale last year, serial numbers unknown. The other had its original speakers, date code "LC25" = 25th November 1970 for their manufacture.
Serial number 1133, with white drawbar ends, also has speakers made at some point in 1970 - date code only partially legible.
Below, details of the drawbar assemblies: on each "L-shaped" bracket, a knurled aluminium disk driven by the movement of the bar. The disk in turn drives the potentiometer on the other side of the bracket.
20th January (2)
Extremely scarce these days, a Jennings Attack Percussion unit, designed to attach to any organ, manufactured for JEI by Triumph. Tom advertised the units relentlessly in "Exchange and Mart" magazine in the early 1970s, but sales are likely to have been slow. Few have come to light.
"Exchange and Mart", August 1969, Jennings still "Jennings Electronic Developments".
20th January
The holding page for the Jennings J70 two-manual organ, which succeeded the J68 in early / mid 1970, has been filled out a little, prompted by the recent appearance of two examples, one in slightly peculiar circumstances. There is a good deal more to come.
The precise point at which the J68 became the J70 is not possible to isolate at the moment - summer 1970 seems most likely. For a time Jennings simply made reference to its "two manual" and "three manual" models in its adverts.
