LARGE BOX AMPS - SOLID STATE RECTIFIED - late 1965 to early 1966

Serial numbers in the 4000s

Again, AC50 Mark 3s continued to be assembled for Vox by and in the Vox/Burndept factory at Erith. The majority were produced by the latter. Capacity at Triumph was extremely limited.

It is worth reiterating that Triumph brought together chassis, boxes and serial number plates in a fairly random way. Late chassis can therefore have early serial number plates and vice versa. Burndept was far more orderly.

Some of the Triumph-made AC50s have boxes with white warning plaques when the norm was red. One simply has to put anomalous amps to one side and take them case by case - for instance, on this page serial number 2300 which has a brimistor (late amp in "early" box), and number 4131 (early amp but late serial number).

Burndept always stamped its chassis with serial numbers - on the aluminium flat of the preamp underneath the jack sockets.

These numbers do not correspond to any sequence of assembly or registration. Unpopulated chassis, already with numbers, were simply kept in piles in no order. The nearest one was grabbed when a new amp was to be made.

One can see various examples of these stamped numbers below. Triumph chassis are always unstamped.

Many chassis now have the , a heat dependent resistor, added to help delay surges when the amp was switched on. The brimistor is positioned to the left of the main power valves, in effect where the GZ34 rectifier stood in .

Note that the new chassis required three holes (where before there had been none) - two for the brimistor supports, and a large grommeted pass-through behind it to the underchassis. Brimistors were often removed by service engineers, but the tell-tale chassis holes naturally remain.

The brimistor is noted on the schematic OS/072 - for which, - as an addition of 14th October 1965. Howeever, one should not place too much reliance on absolute date. Schematics were drawn up for service engineers, not assembly.

Serial number plates are sometimes two line, sometimes three - there is a definite cross-over between the old and new type.

Below, a register of amps. If anyone knows of others that have not yet been included, as ever do let me know.

Serial number 4040 - currently in the USA

Serial number 4061 - currently in the USA

Sold on ebay.

Serial number 4083 - currently in the USA

Assembled by Burndept - the stamped chassis number visible under the input jacks.

Serial number 4095 - currently in the USA

No brimistor. Chassis number tantalising indistinct. Good condition all round.

Serial number 4114 - currently in the UK

Serial number 4131 - currently in the USA

No brimistor. The amp is certainly Triumph made. Pot codes "AM" and "BM" = Jan. and Feb. 1965. Is the box earlier? Note the white warning plaque; the absence of a mains socket on the back panel; and the position of the serial number plate over to the right. For a similar older box with a Triumph-made AC50, see below, serial number 4918.

Serial number 4133 - currently in the USA

Excellent condition. Three-line serial number plate; red warning plaque. Chassis number 1092. The Bulgin mains connector probably, and the 1/4 jacks certainly, a later addition. The amp is currently (21st Dec.) advertised here. Pictures originally posted here

Serial number 2300 - whereabouts unknown - possibly reboxed (or Triumph simply using an old one)

Chassis no. 1645. Assembled by Burndept. Probably reboxed. The chassis is consonant with an amp in the 4000s - note the rectifier diodes - not with an amp in the 2000s.

Serial number 42xx - currently in Europe

Serial number 4252 - currently in Europe

In really condition. Three-line serial number plate, red warning plaque, no brimistor. Chassis number 1292 - so the amp was assembled by the Burndept factory. The amp is currently (Dec. 2012) presented for sale here. Thanks to Detlef for the pictures.

Serial number 4256 - currently in Europe

A nice Foundation bass rig.

Serial number 4282 - currently in the USA

Chassis number 1108. No brimistor. A great amp, in fabulous condition. Pot codes are "GM" = July 1965.

Serial number 4316 - currently in the UK

Serial number 4320 - currently in the UK


Serial number 4414 - currently in the USA

Serial number 4417 - currently in the USA

Thanks to Gene for the note on the existence of this amp

Serial number 4508 - currently in Europe?

Assembled by Burndept - the stamped chassis number visible under the input jacks. Voltage selector set to 225V.

Serial number 4513 - currently in Europe

Serial number 4540 - currently in the UK

Serial number 4553 - currently in Europe?

Serial number 4566 - currently in the UK?

Serial number 4651 - currently in Europe?

Three-line serial number plate, but white warning plaque. The voltage selector is set to 225V.

Serial number 4677 - currently in the USA?

Probably assembled by Triumph? No sign of any stamped serial number on the chassis. Mustard and WIMA capacitors in the preamp. This amp is listed here (no affiliation).

Serial number 4684 - currently in the USA?

Serial number 4702 - currently in Europe

Excellent condition

Serial number 4750 - currently in the UK

Serial number 4756 - currently in the UK

Sold on ebay in late 2014. Chassis no. 1463.

Further pics.

Serial number 4774 - currently in the UK

Great condition, and with what looks to be its original cover. Pictures originated here.

Serial number 4852 - currently in the UK

Chassis number 1690. Great condition. Inspection tag still on the underside tagboard.


Serial number 4885 - currently in Holland

Serial number 4918 - currently in Germany?

A Triumph-made amp. Note the early box: white warning plaque; absence of back panel power connector; and serial number plate over to the right. The amp has no chassis number. The preamp is populated with mustard caps.

Serial number 4920 - currently in the USA

Accompanied by a Vox Sound 2x15" cab and repro trolley. Cab and amp regrilled with brown cloth. Note that on the back panel, the holes for the speaker connectors were originally designed to receive Amphenol connectors (which did not come in until mid 1965).

Serial number 4922 - currently in Europe?

Assembled by Triumph. Three-line serial number plate, but white warning plaque. The voltage selector is set to 225V.


Serial number 4987 - whereabouts unknown

Serial number in the high 4000s or 5000s - currently in Europe