Click for a larger image, as ever. The date code on the red CCL capacitor is printed in plain - DEC 68. Detail from the preamp of Defiant no. 2032, a strange one. See further on this page.

As has long been known, date codes of components are a valuable means of establishing dates *after which* an amp must have been made - termini post quem. Clearly one does not know how long a capacitor, for instance, lay in its box or bin at the Burndept factory before being used, but the dates provided are nonetheless useful and sometimes extremely revealing.

By and large the codes themselves are fairly straightforward: year and month are given in the form either of a number and letter, or two letters.

The month is always a letter: A-L = January-December. In the case of American-made Lemco capacitors and RCA transistors, however, "I" was skipped, so A-H = January-August; J-M = September-December.

The standard British letter code for 1966 was "X". 1967 = "Y" and 1968 = "Z". The alphabetical sequence started again with "A" in 1969.

In general terms, the axioms are: identify as many codes as possible on a spread of components (making sure that they are indeed original), and always use the *latest* as a terminus post quem for the production of the amp.

YELLOW LEMCO CAPACITORS - 1966 and 1967 only

These are found in the preamps of JMI-made solid state amps, i.e. ones made in 1967. The successor company of JMI - Vox Sound Equipment Ltd - went over to Mullard mustards for signal caps and blue Philips for coupling caps.

The code on both Lemcos is "YB". "Y" = 1967, "B" = February, thereby giving us a starting point. The red CCL cap. left of picture also gives Feb. 1967 in a different format (see immediately below). For the date codes of the Mullard mustard caps used in later (VSEL) amps, see lower down this page.

RED CCL FILTER CAPACITORS

These were used throughout the solid state range until the end of production, c. 1972.

Most CCL capacitors have a letter and number code for month and year. In the capacitor pictured above it is at the end of the printed text: "L6" = December 1966. The amp: an early Conqueror.

Evidently this capacitor was a least a couple of months old before being used. Pre-production amps were still being signed off in January.

RCA TRANSISTORS

The code is a number for year, and a letter for month (skipping "I", as mentioned).

Above, a detail from Supreme no. 1258. The code is 7M = December 1967. The power section of this amp, which is a standard JMI unit, was either finished off by JMI in early 1968 (soldering on while still in the hands of the receiver), or by VSEL later in the year.

WELWYN CEMENT RESISTORS

These are found in the bias string of the power amp, and on the output board of the underchassis. As above, a number for year, and a letter for month (skipping "I"):

Above, the bias boards of Supreme no. 1087, badly damaged by the heat generated by these resistors. Being on the rear of the boards, they are normally hidden from view. The date codes are "XL" = 1966, November.

The positions of the boards are indicated on the pic below:

MULLARD MUSTARD CAPACITORS - post 1968

The date codes of Mullard mustards are slightly different. Letter A-D for the quarter of the year; a number for the year; a letter indicating the factory.

Above, a detail of the preamp of a VSEL Supreme. The cap. in the upper right of the pic. has the code "D8N" = last quarter of 1968, either the Southend factory (not Blackburn as originally stated), or Foots Cray in Kent, only a step away from Erith. These caps were made in great quantities, so it is not unusual to find some early ones in relatively late amps.

Defiant no. 2243, "Vox Sound Ltd" on the serial number plate, but "Vox Sound Equipment Ltd" control panel, so assembled in late 1969. Above, a shot of the CCL capacitor with date code "D9" = April 1969. The blue Plessey caps have "C-9" which probably means March 1969 - either that or third quarter of 1969. If anyone has a reliable source for Plessey codes, do let me know.

Vox Foundation Bass no. 2813, close to the end of the run. RCA transistor with code "2D" = April 1972.

Heat sinks from a broken Vox solid state PA amp. The RCA transistor have codes "3H" = August 1973. These amps were made after production of the guitar and bass amps had stopped.

Vox Supreme no. 2510, Vox Sound Ltd. Mustard capacitor with code A0W = first quarter of 1970, Wembley factory. Other observable mustard caps have "D9", no factory designation = last quarter of 1969. This amp was paired - perhaps at the factory, though there is no proof absolute - with a Vox Companion 4x12" cab with Celestion T1925s dated "HE" = August 1972.

Probably in the early 1970s it took a good while for stock to sell. Vox Sound Ltd evidently struggled.