A pre-production Vox Supreme power section

currently in the UK

The pre-production Vox Supreme power section illustrated on this page came to light in an amp that appeared on ebay in Germany in mid 2023. Its constituent parts were: (1) - a standard late JMI preamp; (2) - a "Vox Sound Equipment Limited" (1968 to late 1969) box that had never been fitted with a serial number plate; and (3) - the pre-production power section.

The absence of a serial number plate - no screw holes present anywhere on the back panel or underside - tends to indicate that the amp as it exists now was some sort of one-off, at any rate, not part of the production run.

The preamp has the latest JMI number that has so far emerged: number 2448. The sequence began at 1000. Treble preamps were common to the Vox Virtuoso, Conqueror, Defiant, as well as to the Supreme.

Just to add that numbers of late JMI amps were put together from older parts and sold in early days of VSEL is clear from survivals.

Notes on other pre-production JMI solid state amps .

Treble preamp Serial No. 02448.

Below, some details of the power section, which was produced at some point in the second half of 1966. The orange 2250uf Plessey capacitors are dated "JUN 1965", the grey Radiospares 5000uf cap. "PXB" = February 1966. The Radiospares cement caps have "XC" and "XE" = March and May 1966.

Three of the main power transistors (2N3055s) are branded "ITT". The fourth (pictured) is unbranded, the print giving only "2N3055" and "6 R". Whether "6" stands for 1966 is unknown. The wiring loom is extremely tight and all solder joints are apparently original, which is to say that the transistors have a good chance of being original too.

Right-hand bias board. One of the cement resistors in the bias string has the date code "XE" = May 1966 for its manufacture.

The unbranded 2N3055 with "6 R". The other three power transistors are branded "ITT".

The four heatsinks on which the transistors are mounted are fixed to the upright of the chassis with four 4BA machine screws (and nuts) each. It is impossible to remove the middle pair of heatsinks without first removing the mains transformer - not an ideal arrangement where repairs/replacements are concerned.

Underchassis

Two of the main rectifier diodes removed. The remaining two, which may be replacements themselves, are BY255.

2N3054 transistor mounted flush on the chassis (no socket), wires soldered directly onto the legs of the collector and base.

Cement resistor with date code "XC" = March 1966 for its manufacture.