A Vox AC50 mark 1 try-out
Sold in the liquidation sales of 1967 and 1968?
Updated 8th December, 2025
On this page, pictures of an AC50 Mark 1 probably bought incomplete at one of the JMI liquidation sales in late 1967 and 1968. By the 1980s it had found its way to Los Angeles, and from there to Japan. It is now back in the UK.
So far as one can tell the amp was a sort of a fairly advanced tryout for the new model using Woden transformers, the green-shrouded mains of a type not found in other early AC50s (part number 73631?). Its date code - and that of the choke - is "LU" = November 1963. What became of the output transformer is unknown. A completely unsuitable Schumacher was evidently added in the USA in the 70s or 80s. For more on the Wodens, see the section towards the end of this page.
Other components also have 1963 date codes:
- the grey Radiospares electrolytic capacitors (16uf and 32uf) in the preamp "PUJ" and "PUK" = September and October '63;
- the blue Hunts 16uf cap. in the preamp "SHI" = 52nd week of '63.
- the 470 ohm Radiospares cement resistor on the bias board "UC" = March '63 for its manufacture. Its companion - the 270 ohm resistor - is likely to be of the same date (old-style Radiospares logo);
- one of the main RS filter caps "UG" = July 1963;
Certain elements are obviously later however, presumably being replacements for things that were either spent or perhaps even missing when the amp came up for sale in '67/'68. The second of the two main filter capacitors is a Radiospares from 1968 (dated 21st week) for instance; and the 25 ohm current limiting resistor for the GZ34 has "BC" = March 1970.
Also of note: a black traffolyte control panel (a small batch of these appeared in late 1967); three potentiometers of the wrong values: 250K for the volume, 500K for the treble and bass, to judge from their appearance, probably added in the '80s or '90s. Those have since been replaced.
Probably hand-in-hand with the revamping of the electronics, the case was recovered and the original brown grille cloth replaced with black.
Older pictures of the amp can be found on the main page on the AC50 Mark 1 (late 1963 to mid 1964).
Click as ever on the thumbnails for larger images.
The factory cutouts on the back panel were for a Bulgin mains socket and a Cannon XLR-3-13 speaker socket.
Later jack sockets.
Chassis and inner face of the back panel. The output transformer is a new replacement.
Woden choke, date code "LU" = November 1963 for its manufacture.
Hunts capacitor with date code "SHI" = 52nd week of 1963.
The Radiospares 32uf cap., date code "PUJ" = September 1963.
The date code of the 470 ohm Radiospares cement resistor: "UC" = March '63.
The bulge in the later of the two filter capacitors (see below).
The Radiospares capacitors that came with the amp, the one on the left made for RS by TCC, date code "UG" = July 1963; on the right the later cap, dated 21st week of 1968. The latter is completely dead.
Later holes drilled in the base of the case.
The locating groove for the back board, which has a corresponding tongue, ensuring that the board cannot be mounted upside down.
The transformers and wooden case
The Woden transformers used in this amp are likely to have been part of a batch ordered by JMI somewhere around October '63, the date codes of the units in view being "LU" = November 1963. At least one other amp will have been assembled with other transformers from this batch - the "model" sent by JMI to Triumph to be copied for production runs. This was later purchased by Graham, the "chassis beater" at Triumph. It expired on stage one evening at the Shepherd's Bush Empire.
Whether the two amps consigned to The Beatles in December 1963 had Wodens is not known. The strongest sense - for the time being at any rate - is that they were simply among the first to have been assembled by Triumph (transformers sourced by Triumph, not JMI). All will become clear in due course however.
That the amp illustrated on this page was prepared (in late 1963 or early 1964) for use beyond the walls of Dartford Road is highly unlikely, as has been mentioned. No further instances of Wodens in early AC50s (Mark 1s) have so far come to light.
AC50 mains transformer, part number 73631, date code "LU" = November 1963. The pattern of holes around the cut-out for the output transformer shows that the chassis was made specifically for Wodens, not the type of transformer later used by Triumph.
As the shrouds of Woden transformers did not have secondary fixing points ("ears") for the preamp upright, a rather bodged aluminium bracket was made up. Westrex fitted the Wodens used in AC80/100s with a small iron bracket, a reasonably tidy solution. Without support at transformer level, the preamp upright would be unduly fragile.
AC80/100, Woden mains transformer, part number 72191, date code "MU" = December 1963.
In late 1964, JMI came back to Woden for the short initial runs of AC50s produced by Burndept. These later transformers (date codes from August 1964 to February 1965) have plain metal shrouds, much as on those used for the AC30s and AC80/100s of the time.
The case
A further quirk of the amp, or rather its case: two screw holes on the upper edge of the back panel with corresponding cage nuts (2BA) on the preamp lip. The holes are original to the board. There were no others. Almost all production amps have only one screw on the upper edge of the panel, generally dead centre, self tapping, and no cage nut on the preamp lip.
The only real parallel for the back panel of this amp comes in the shape of the amps issued to The Beatles in late December 1963.
JMI were evidently extra cautious early on - perhaps because the transformers were Wodens and had no fixings on their shrouds for the preamp upright?
Rear of George's amp, Olympia, late January 1964.
The new page on the amp can be found here.