AC100s made for Vox by Triumph Electronics, Purley

AC100 Mk 2s (fixed bias)

On the Triumph premises in Purley, . Triumph also assembled for Vox in the mid 1960s the 4 and 7-series amps, a range of , and assorted effects units. In the earlier 1960s the company produced the AC10 and AC50.

When the contract with Vox ended in 1967, Triumph went on to make its own line of amps - - as well as assembling those designed by other makers.

To date (2013), all the Triumph-made AC100s that have come to light have fixed bias circuits (AC100 Mk2s). Cathode biased amps, insofar as they survive, seem to have been made by Westrex and Burndept. As ever, if anyone has any info, please email me at .

Triumph-made AC100s are distinguishable in various ways: - transformers with unpainted, unmarked shrouds (sometimes the units are slightly larger than the "standard" black ones used by Burndept); highly twisted transformer leads; orange grommets for the holes in the chassis; shorter than normal preamp tagboards; mixed sets of resistors; "mustard" capacitors; peculiar boxes; and boxes with peculiar serial plates/warning plaques and so on.

On the left, the short Triumph preamp board. On the right a standard one. Note the relative positions of the capacitors on the far left to the left-most preamp valves. Note too in the first picture, the unused hole under the capacitor.

Also, to express "negative" characteristics, one does not find the red dye on the solder joints that Westrex used; nor, normally, are there the chassis numbers that Burndept employed.


Box with serial number 444 - currently in the USA

The first three images from Jim Elyea's book, Vox Amplifiers. The JMI Years. The fourth image, far right, is of a Triumph-made AC50 recently on, for comparison. Note the highly twisted leads of the transformers and the initialled chassis. "DE" is Dave Earp, who signed a number of AC50s too. The serial plate on the AC100's box - 444 - is completely out of sequence in relation to the Burndept-made amps. Triumph used all sorts of boxes for their amps, some with "impossible" serial numbers. See below. The preamp tagboard looks as though it is as short as the ones in other Triumph-made amps, ending in line with the volume pot (rather than the input jacks); and the capacitor clamps in the preamp look similar too. New components can be seen alongside original ones (at least one "mustard" capacitor remains).

Box with serial number 844 - currently in the USA?

Sold on ebay in March 2012. A near immaculate AC100 rig. As in the amp above: a short preamp tagboard, plain metal shrouded transformers (and heavily twisted leads under-chassis), orange grommets where wires pass through the chassis, large clamps for the preamp filter capacitors, and green resistors and "mustard" capacitors. The amp is also registered on the .

Date codes of three original speakers in the cabinet are 06AK, 02HK - January and August 1965. The fourth, probably a replacement, is 30HL = August 1966.

A date late in 1965 or early 1966 seems likely for the production of this amp. Signed by "Graham", as serial numbers 1071, 1674 and 1752, below.

Box with serial number 1071 - currently in the USA

Short tagboard; mustard capacitors; silver-topped transformers. Chassis signed by "Graham" as numbers 844 (above), and 1638, 1674 and 1752, below.

No.8 - serial number 1410 - currently in Italy

Perhaps signed by "Graham" - signature in much the same position as other amps on this page. No chassis number. Note the guard around the valves, short tag board, the insulated stand-offs under the fuse-holder, and the large transformers with bare metal shrouds. The latest visible component date codes are one of the blue Hunts capacitors with "HUS" = 26th week of 1965, and the gold-coloured Dubilier cap with "WK" = October 1965. Pictures originally .


Box with serial number 1532 - currently in Europe

Short tagboard, transformers with plain metal tops, insulated stand-offs under the fuse holder. The latest component date code visible is "HUS" on one of the blue Hunts capacitors = 26th week of 1965 for its manufacture.

Box with serial no. 1540 - currently in Germany

Short tagboard, mustard caps, orange/yellow grommets, and large capacitor clamps, as in the amps above. Thanks to Markus for the pictures.

Box with serial number 1638 - currently in Spain

Accompanied by a later 2x15" cab. In the amp, note the short preamp tagboard, the mustard caps and assorted resistors, the three-part fuseholder, and the small pilot lamp. The chassis is signed by "Graham", who signed numbers 844, 1071, 1674 and 1752. The mains transformer is a replacement (dated April 1968). Thanks to Juan for the pictures.

Box with serial number 1674 - currently in Connecticut

Another nice AC100, original XLR and mains connectors still on the back panel. The mains and output transformers have the unpainted tops typical of Triumph-made amps. Underchassis (power section) signed by "Graham", as serial numbers 844, 1071, 1638 and 1752.

Box with serial number 1752 - currently in the UK

A great amp. No visible changes to the original circuit. The output transformer is turned transversly (to the norm) and bolted to the valve guard. This amp appears to have an adjustable bias - the sliding resistor on the underchassis board. Built by "Graham". The box has a red warning plaque. Thanks to Alex for the pictures.

Eight later Triumph-made amps

The six amps below all found their way overseas - the first to Australia, two to the USA, and the other three to Japan (though the first of those is now back in the UK). Numbers 1, 2 and 3, as can be seen, are very close in appearance and arrangement. Codes on the capacitors of no.2 indicate a date in or after 1967. No. 2 probably did not leave the UK until after June 1982 - see the sticker on the preamp chassis.

Perhaps some of these amps/chassis had been languishing there and were given "spare" boxes to make them saleable in the 1980s. But it may be that boxes and chassis were originally brought together at Triumph at around the time that JMI began to totter (from August 1967), unused or perhaps even defective boxes having been sent to Purley, where Triumph was based, from Dartford or Erith. No. 3, though, was certainly sold without a box.

Note that the chassis are not welded, unlike those made by Burndept - see any of the chassis illustrated on. The metal is simply folded over. The likelihood is that the chassis for Triumph-made amps were made by Triumph's contractor in South Croydon - see the recollections of Dave Roffey on the page.

No.1 - thin-edged box, no serial number plate - currently in Australia

Beautifully clean. Has a Triumph plaque affixed on the front edge of the chassis. Note the similarites with no. 2 below - the transformers, the mains light with metal surround, the vertical fuseholder, and the link voltage selector. As indicated on , the box is evidently not a typical thin-edged box - various features are lacking (such as internal bracing for the sides). Possibly it came to Triumph in a defective/unfinished state and was tidied up for this amp.

No.2 - small AC50 box with AC100 serial number plate 1337

In Japan from 1982-2010, currently in the UK

Resides in a small AC50 box with black cloth and individual letters - V O X - in the logo. The back panel, showing signs of having been cut down, probably from an AC30 - the cut-out is for a top-boost unit. The power tagboard (underside) has had a small burn-out. The on/off switch is an old Lucas switch for a car's ignition. This is a good-sounding amp. Pictures from the seller's website now added (first two).

No.3 - currently in the USA

A good late Triumph amp similar to the one above - note the mains pilot light and voltage selector - in a custom made AC50-sized box. The speaker cab contains 2 x 14" Wharfedales. Thanks to Anthony for the pictures and information - the AC100 was purchased at the Vox factory in a liquidation sale in 1968, one of two that were being sold simply as chassis. The other had a black plastic panel, presumably similar to the panels below:

Panel on the left: bought on ebay and added to an AC100 Mk2 from mid to late 1965. On the right: belonging to an AC50 assembled by Alan Pyne.

No.4 - serial number unknown - currently in Japan

Pictures 1 and 2 show the output transformer in course of replacement. Note that this amp has a surround for the main power valves. No.2 does not, and has no holes in the chassis for one to be affixed. For the owner's fine collection of Vox amps - .

No.5 - box with serial number plate 1555 (and white warning plaque) - currently in Japan

Pictures posted in 2009 by the Japanese shop TCGakki ( . The site is still live 8th May 2010. The mains transformer looks like a standard AC100 Mk2, unlike those in those of the other two amps in this group. The output transformer looks as though it's a replacement of some sort - possibly a Fender. Note in the last but one picture, the stand-offs (underneath the fuse holder) for the 6.3V supply line to the preamp. Stand-offs of this type are a feature of the Vox 7-series amps, the chassis of which were assembled by Triumph Electronics 1966-68.

No.6 - box with white warning plaque and impedance selector - currently in the USA

A nice late Triumph-made amp with impedance selector and more recent bias adjustment circuit. Short tagboard, as the other amps on this page, and no stamped chassis number. Just visible in the fourth picture, the chassis standoffs for the 6.3V heater supply, as in the amp above. Thanks to Gene for the pictures.

No.7 - currently in France

Signed by Graham. No serial number plate remains though one can just about make out the holes on the back board. Note the eyelet tagboard in the preamp. Accompanying the amp, a 2x15" cabinet with two (extremely under-rated) Goodmans Audiom 81s. Thanks to Bill for the pictures.

No.8 - currently in Sweden

Owned and used by the Swedish band "The Mainliners". Built on the earlier style of AC100 Mark 2 chassis with no guard around the EL34s. Probably made in 1966/1967. The amp had no back panel. Some later work at the mains input stage - a standby switch added and fuse holder under the preamp lip - but otherwise very few changes to the upper chassis. Some renewed components (as one might expect) in the underchassis power section.

The cab is a Jennings (JMI) Supreme cab from 1967. It is just possible that amp and cab were paired early on. There were definite efforts to move valve stock in 1967. Late JMI AC50s were certainly paired with new style (solid state) Foundation Bass cabs. Thanks to Magnus for the pictures.

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