Vox AC30: Burndept chassis numbers

Late 1962 - early 1968

Numbers 01000 - around 14000

In order to meet growing demand, in mid 1962 JMI contracted Burndept Electronics, based in Erith, to assemble batches of chassis in addition to those already being assembled by Westrex.

The two companies were not only responsible for making the chassis (the metalwork), but populating them with components, checking and testing, and so on - in other words providing finished, working electronics.

Burndept-made chassis are identifiable in several ways: early on by the use of Woden transformers with green coloured shrouds (Westrex used Haddon and Albion); small cut-outs for the cage nuts in the aluminium preamp upright; and by the presence of stamped chassis numbers.

A Burndept-made chassis from early to mid 1963. Green-shrouded Woden transformers, and a chassis number stamped in front of the output transformer.

Details from serial number 6097. The cut-outs for the aluminium preamp upright marked with arrows. These cut-outs do not figure in the chassis made by Westrex.

Westrex did not stamp its chassis. Nor for that matter did Burnham Engineering (based in Dartford), which did a large proportion of the metalworking required by JMI from 1957 through to the winter of 1961 (the last of the AC30/4s). The chassis that Burnham made were populated with components, however, at 115 Dartford Road.

Initially, Burndept stamped its numbers on top of the plinth in front of the output transformer. From early to mid 1963, the stamps were made on the aluminium preamp upright, beneath the voltage selector. The sequence began at number 01000. The change of position - stamping on the aluminium preamp upright - probably came in at chassis no. 02000.

From around chassis number 3000 in 1964, chassis were given colour codes to indicate voicing (Treble, Bass, Top Boost) - .

In late 1966 or early 1967, the position of the chassis number was changed again - to the left hand side of the preamp chassis above the speaker terminal block, as in AC50s and AC100s.

While chassis were certainly stamped in order, it is not clear yet whether they were assembled in order on the Burndept work benches. Evidence gleaned so far suggests that they were not.

Also to add that chassis, once finished, were neither stored in order, sent to JMI in order, nor fitted into AC30 cabinets in any order when the time came for an amplifier to be made up for sale.

One cannot date AC30s therefore by these numbers. The same is true for the other models of amplifier chassis - T60, AC10, AC50, and so on - assembled by Burndept for JMI.

Below, pictures to illustrate the location and format of the Burndept stamps. These will be added to in due course.

A small quirk of the AC30 chassis made under contract for JMI by Burndept from late autumn 1962 - the small cut-outs in the aluminium preamp upright for the cage nuts. Chassis produced by Westrex do not have these; nor the early chassis made by Burnham Engineering (Dartford).

(1) - winter 1962 to mid 1963

Chassis numbers 01000 - around 01999.

The 29th chassis stamped with a number by Burndept, the lowest Burndept chassis number encountered so far. The serial number plate unfortunately has parted ways with the amp.

Detail of serial number 6097, below. Chassis numbers begin at 1000, but they were not used in any particular order.

The designation "AC.36" was simply the early short-hand for AC30, six inputs. As production proceeded, the format became "AC30/6", the earliest known instance currently being 01518, below.

Chassis number 1518. Serial number unknown, probably in the high 6000s or low 7000s.

The 945th chassis *stamped* by Burndept. Not the 945th completed. The number is stamped on the plinth. The serial number of the AC30 is unknown

(2) - mid 1963 to late 1966

Chassis numbers 02000 - around 12000(?).

The highest number currently known (Nov. 2020) in this position - on the right-hand side of the preamp - is AC30/6 SER. No. 11371: AC30 Super Twin serial number 5031.

Chassis number 02238, stamped on the aluminium upright. AC30 serial number 9434.

Chassis number 11371, AC30 Super Twin serial number 5031.

(3) - late 1966 to early 1968

Chassis numbers 12000 - around 14000.

The lowest number currently known (Nov. 2020) on the left-hand side of the preamp is the one below, 12021. The serial number plate of the amplifier - an AC30 Twin - is missing. The highest known at present is 13622.

Chassis number 12021, stamped on the left-hand side of the preamp.