VOX AC100 - UPDATES AND NEW INFO
"Beat Instrumental" magazine, December 1973 - the new-style JEI 30. Note that the amp pictured has controls at front. Surviving production units have controls on top.
Recently on ebay, a Vox 100 public address amplifier from 1966 or 1967. For more on these amps (which were produced by Triumph Electronics for Vox), see this page.
18th February (3)
The back cover of "Beat Instrumental" magazine, February 1966. One of the last UK adverts to feature the AC100.
18th February (2)
"Beat Instrumental" magazine, January 1966. The fire at the Erith Works in December 1965. For pictures of the works, see this page.
A note published in "Beat Instrumental" magazine, November 1965, on new amps issued to the Beatles by Vox. These were the AC100s seen on stage at Sheffield and elsewhere in December 1965. The amps were subsequently given to the Bee Gees. One remains in Florida. See the posting here.
Snippet published in Beat Instrumental magazine, October 1964, on the Beatles' AC100s at the British Musical Instruments (Association of Musical Instrument Industries - AMII) Trade Fair, Russell Hotel, London. The Fair ran from 24th - 29th August.
Just to add that at the time of the BMI Fair, the Beatles were on tour in the States. The "100-watt amplifiers" must have been similar ones brought along from Dartford. At the end of the Fair, JMI secured the deal with Thomas Organ to supply $1.5m of equipment.
Serial number 496 - a "100W Amplifier" (the immediate precursor of the AC100 mark 2) - currently on ebay in the States, along with a repro trolley and repro 2x15" cab. The amp has had a certain amount of new work, esp. the power section underchassis. Output transformer is a replacement; and there is something unusual about the mains unit - the second 6.3V line for the preamp seems to have gone. External condition is good.
The Ottawa Journal, 2nd June 1966. The earliest advert that has come to light so far for a second-hand AC100 in North America.
Given that full rigs were going for around $900-1000 in 1966, the advert above is probably for an amp, cab and trolley set. Below, an early advert in the UK for an amp alone (repeated from a post last year).
Rudall, Carte and Co. advert in "Crescendo" Jazz Magazine, May 1965, for a "Vox 80 Watt Bass Amp", either copper or black panel (too early for a second-hand grey), for £100.0.0 - in today's money £1750.
A bumper crop of AC100s for sale at the moment. Above, serial number 1405 currently on ebay.uk. Metal guard plate around the EL34s. Replaced choke.
A nice early "100W Amplifier" - fixed bias, the immediate predecessor of the AC100 mark 2 - appeared for sale a few days ago on ebay.it. Serial number in the low 500s. For other "100W Amplifiers", see this page.
Serial number 772 - three pics below - has come up for sale in the USA. One of the nicest early AC100 mark 2s.
The advert appeared on Craigslist earlier this week.
Currently on Reverb. The serial number scratched out at some point in the amp's past (no doubt having been liberated from its rightful owner). Red warning plaque, Amphenol connectors, single pin corners = a number somewhere in the region 800-1800.
Some notes on Woden transformers to be incorporated on this page:
AUTUMN 1962:. Batches ordered by Vox for the AC30. These had part nos 66309, 66310 and 66311 (mains, output and choke). Date codes go from H.T. (August 1962) through to A.U. (January 1963) and probably beyond. Mains and output transformers were green, the choke plain.
From a beige tolex, copper panelled AC30. One can just see the green output transformer at left.
Printing style current in 1963 and 1964 (this example from Jan. 1964).
AUTUMN 1963: A new green-topped mains transformer for the AC30 was brought in - part no. 72318 - probably the same as the 66309 but with a different winding structure. Date code J.U. (September 1963) to A.V. (January 1964) and probably beyond. These were used side-by-side with the 66310 output transformer and 66311 choke.
Above, a Woden 72318 in a copper panelled AC30 made at the Vox Burndept works at Erith.
LATE 1963:. Around 120 green-topped units ordered for the first run of AC80/100s. These are part nos 72191, 72192 and 72193 for mains, output and choke. All have date codes M.U. = December 1963.
An early copper panel AC80/100.
UNPAINTED (PLAIN METAL SHROUD) WODENS
AUTUMN 1964 For the black panel AC80/100s: 72191 mains, 72193 choke, and a new output transformer with simplified windings, part no. 79806.
For the AC30, a new set: 76852, 76853 and 76854. Earliest date codes for mains and output transformers are H.V. and J.V. (August and September 1964).
EARLY 1965: New batches of 72191, 79806 and 76854 ordered for new runs of the AC80/100 (grey panels). Mains and output units have date codes B.W. (February 1965), and the choke A.W. (January).
Grey panel, cathode biased AC100 serial number 392.
Grey panel, cathode biased AC100 serial number 392.
Note that choke part no. 76854 was dropped for a few months (it was not used in the earliest fixed bias "100W Amplifiers" - see below) but came back in thereafer. The style of printing changes again:
AC100 serial no. 724. Date code of the choke is "EW" = May 1965. Used in later "100W Amplifiers" and all early AC100 Mark 2s. Note that the resistance is cited.
100 Watt Amplifier
The 100W Amplifier (as termed on its schematic) was the immediate precursor of the AC100 Mark 2. It was fixed bias but had no brimistor. Produced late summer 1965.
AC100 serial number 520, an early "100W Amplifier".
The choke in AC100 serial number 531.
The mains and output transformers, with black shrouds, in the new fixed bias AC100s have part nos 66775 and 66776; the choke with gold-coloured frame is 66429. The five digit code is similar to Woden's. Were these a species of Woden transformer - perhaps made by a subsiduary? There are certainly not Albion, as has long been known.
At any rate the manufacturer that made these units also made the ones that later went into the Vox solid state amps, also assembled at the Erith works. One sees three letters stamped in white ink - note the "GTB" on the choke pictured above.
Mains transformer in Vox Dynamic Bass serial number 1135, late 1967 / early 1968.
The three early Westrex-made AC80/100 chassis below all have numbers scratched on the aluminium above the speaker terminal block - ie. in the same position in which chassis numbers were machine-stamped on later AC100s made at the Burndept / Westrex works in erith:
Above, serial no. 174. "119" on the chassis far left.
Above, an amp with some history, serial number plate lacking. "165" on the chassis.
Where "119" is concerned, the reference may be to "119 Dartford Road", the address of the Vox Works. What "165" refers to is anyone's guess. Ideas?
Below, a Jennings Electronic Industries AC40 (as stamped on the plate) no. 1254, with a purple JEI reverb unit and home-built JEI type box for a VSL AC30 amp. The new JEI purple range was introduced in August 1973 - see this page. An identical reverb unit is pictured here.
The items are currently in Germany.
The AC40 is already registered here
21st January (3)
Relating to this entry, below. Above, a Daly 100uf 500v capacitor from late 1962. Perhaps from a Leak audio amplifier or something of that kind (not a Vox). The date code is "TL": "T" = 1962, and "L" = November. "SCT J4" and "49/28" are likely to be the Daly codes for physical dimensions/characterics. The caps are 1 5/16" diameter, 2 15/16" tall.
Due to the fact that original 100uf filter caps have often been changed in surviving AC100s, evidence of the makes used at various points in production has to be gauged in a series of "snapshots".
For copper panelled amps (serial nos 101-225) the picture is clear: gold-coloured Dubiliers were employed. And gold 100uf Dubiliers were probably also fitted in the grey panel AC80/100s made at the Burndept/Vox Works in Erith from the spring of 1965 (serial nos c. 320-430). But in many of these amps the caps have been replaced.
100uf Daly caps, on the other hand, seem to have been bought in by Westrex (along with new sets of Woden transformers and new batches of TCC capacitors) for the black panelled amps (serial numbers c. 230-330) in late 1964. Shortly thereafter production of the AC100 (AC80/100) passed to Erith. Later on, in the autumn of 1965, Daly was used again however - for the "100W Amplifier" (serial nos 431-724).
Above, the 100uf Daly filter cap in AC100 serial no. 520. The date code is "WD" = April 1965.
21st January (2)
Recently surfaced (end of last year) serial number 2103. The amp conforms to schematic OS/167, first instance dated July 1967 and redrawn in the "Vox Sound Equipment Limited" era (mid 1968 to early 1970), though no AC100 has yet come to light with a VSEL serial number plate. One can see one of the pairs of main filter capacitors, a feature of the new circuit, through the top grille. For further late amps of this type, see this page.
Number 2103 is currently in Germany, where it has been for some time. A good number of these late AC100s were exported to Europe; a few also to the U.S.A.
The chassis made at the Burndept / Vox Works in Erith for the grey panel AC80/100s - serial numbers 320-430 - have distinctive cut-outs for the main filter caps: notably two semi-circular excrescences to the main roundel.
These excrescences are not found in the earlier chassis made at Westrex, nor in the chassis later made at the Erith works for the "100W Amplifier" (serial numbers c. 431-724).
20th January (2)
Above, two preamp valve cathode bypass capacitors - Hunts 25uf - from AC80/100 serial number 392. They had both bubbled out. Date of manufacture is given in "I YT". For an overview of the Hunts date code system, see this page on the AC50 website.
Effectively "I YT" translates as "3 04" which should mean the 4th week of 1963. But Hunts was often quirky in stamping its codes, and it is possible that "3 04" was actually intended to mean the 30th week of '64.
Above a Daly capacitor from a late Westrex-made cathode biased AC80/100 - before and after some cleaning of the paint this morning. The amp is pictured here and below. One can now see the date code: "VK" = October 1964 - much in line with the dates of other components: TCC capacitors in the preamp "VJ" and "VK"; cathode bias resistors and capacitors (also TCC) which still survive, "VK".
Left, one of the pics from ebay July 2007. Centre, the amp as it now is, with a replaced mains transformer (from an AC100 Mark 2, new shroud). Right, a pic of the preamp by the input jacks. The box is probably from a later amp (serial no. 1297 on the plate).
The amp has for some time had a grey panel. However, it may not be original. As the third pic shows, two holes for extra inputs (?) were made in the aluminium chassis at some point. These do not figure on the current panel.
It seems possible, given the dates of the components in the amp, that if there was indeed a predecessor panel it was black. Note that the shroud of the mains transformer in serial no. 262 has the code "KV" = October 1964.
On the other hand, it could simply be that the existing panel was taken off for the making of the holes and then, after a change of mind (ie. a decision not to make holes in it), put back on untouched - in which case the amp must have have been one of the first cathode-biased AC80/100s to have been done in grey - a serial number potentially therefore in the 290s or low 300s.
But to go to all the bother of taking the panel off, making the holes, and then sticking the panel back on seems a little perverse. The first scenario - that the current panel is in fact a replacement for a hacked original - seems most plausible.
The spraying of the steel chassis black - done at a guess in the 70s - was presumably an attempt to retard heat. Up until 2007 the amp had its original Welwyn 270R cathode resistors (which still survive, as mentioned, along with all other original components now removed). Clearly at some point their value shifted: they currently measure around 250R. The valves and transformers will have run very hot indeed.
The sprayer did a relatively good job, but missed the backs of the transformers and managed to get the bat of the mains switch.
The gearing up of Westrex for new runs of AC80/100s in late 1964 doubtless came as a consequence of orders coming in from the USA - JMI's deal with Thomas Organ was struck in August. See the info being assembled on this page.
Serial numbers 236 and 262 have probably long been in the States - 262's cab (an SDL) unfortunately perished. Midax horns said to be from it still exist. However, numbers 249 and 276 were bought from new in the UK; number 269 was exported to Finland.
Just to add, that the majority of amps with serial numbers in the range 230 - 300 will have been made between November 1964 and February 1965. Remember that component date codes are simply a terminus post quem - a "date after which" - for the making of an amp. We do not know precisely how long capacitors / resistors / transformers sat on stockroom shelves - probably not long, but there will always have been exceptions.