Thick-edged box; copper control panel; diamond inputs

Probably around 250-300 made

diamond input vox ac50, second quarter of 1964

With the "diamond input AC50", as it is commonly called, Vox introduced two changes: - a thicker box, and four inputs. Viewed from the back, the far left input is higher gain than the other three. The idea was to make the amp as versatile as possible, Public Address applications included.

Early two-input AC50s .

The chassis were manufactured for JMI by Triumph Electronics, Purley Road, Croydon in the second and third quarters of 1964. The finished units were taken to Dartford (as the earlier amps had been) by Geoff Johnson, owner of Triumph, and back panels (with serial number plates) and boxes provided.

Serial numbers are therefore not a reliable guide to the relative date of these amps.

No dedicated schematic for the diamond-input version of the AC50 survives (and perhaps none was produced). The circuit is that of the two-input amp.

GENERAL CHARACTERISTICS: single channel; link voltage connector; slots in the aluminium preamp chassis to allow the fixing of transformers of different heights; metal grille at top of back panel; 6 holes in the chassis plinth for each transformer, allowing use of units with centre as well as corner fixings.

At least two amps have linear pots for their treble and bass controls, instead of the logarithmic pots specified in schematic OS/044. As ever, the wiring of the controls varies - in some amps it was reversed: ie. the controls work "backwards".

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


Serial number 1120. Currently in the USA

A nice diamond-input AC50 in a thin-edged box. Amp together with the cab and trolley picture were purchased as a set around 20 years. The story at point of sale then was that the amp, cab and trolley had been left under the stage after the Beatles' concert at Jacksonville (11 September 1964) and "found" or "rescued" in some way. Utter nonsense and not the sort of thing to impart confidence in the integrity of the set.

The cab is certainly a genuine Vox cab - an AC30. No doubt about that. But the trolley could well be a repro, the three things having been brought together to make a set that looks like the amp pictured in the brochure below. This not to say there's anything wrong with amp, cab or trolley, quite the opposite in fact. They're superb - it's just a question of whether they have always been together (i.e. since 1964).

Thomas Organ advert, early 1965

Royal Guardsman: the cab in the picture is an AC30 - count the number of diamonds on the front - 17 1/2 wide. The description describes a later AC50 amp and cab, however. Picture and text are not in step.


Serial number 1161

Sold on ebay late March 2013, further details to follow.

Above, new pictures of the amp. Thanks to Guy.

Another two images, one during the course of tidying up; the other with companion on small box cabs - wonderful stuff. Smooth grey tolex.

Serial number unknown - currently in the UK (?)

Sold on ebay in 2007. Immaculate condition, complete with original cover and leads. Single speaker output. Smooth grey tolex.

Serial number unknown - currently in the USA

Smooth grey tolex. A replacement back panel incorporated the original connectors, otherwise good condition. Large output transformer. Thanks to Steve for the pics.

Serial number unknown. Currently in the UK.

Smooth grey tolex. Cab and amp sold separately by Ampaholics in 2013. The cab is in the UK (further pics to follow). Note the non-standard position of the logo on the amp. Image original .

Serial number unknown - currently in the UK

Used by the Brighton band "The Revivers". Replaced handle; on the back panel (just visible in the photo) two speaker outputs, and the original mains connector. The images were originally . Thanks to Graham for permission to use on this site.


Serial number 118x. Currently in Germany

Currently in Germany - - where it is on offer. Good condition externally. Two jack sockets added at back.

Serial number 118x (?) - currently in the USA?

Sold on ebay in 2006. Originals mains socket and single speaker output in place. White warning plaque centred on back. Logo composed of separate letters: V O X. Note that there is no point of fixing on the upper edge of the back panel.

Serial number unknown. Currently in Australia

Pot codes "BL" = February 1964. Further details to follow.

Serial number unknown. Currently in the UK (restored by ESE Music in Kent)

Pictures from March 2011. Excellent condition. A few replaced components, but all "mustard" capacitors still in place. White warning plaque centred on back.

No serial number plate. Currently in the UK

A fine amp with its original green cover still intact. A replaced handle, speaker socket, and a couple of new capacitors, but otherwise all original. Single letters for the V O X logo, and a Bulgin mains socket. Cannon LNE and XLR mains sockets seem to be a thing of slightly later amps. Thanks to Chris for the pictures.

Serial number unknown. Currently in Japan.

Grille cloth and logo possibly renewed? No image of the control panel available.

Serial number unknown - currently in Japan

A nice amp paired with a repro cab and stand. Unrelated to the amp above - note the wear on the top leading edge.

Serial number unknown. Currently in Australia.

A great amp that popped up recently in England. Thanks to Guy for the pictures.

Serial number unknown - currently in the USA

Pictures from 2007. No shots of the box. Holes for capacitor clamps are diagonal, as in the amp photographed on a black background, above. Note also the lack of underchassis mounting bracket for the mains transformer, again, as above. The volume pot has the code BL = February 1964 as in the case of at least one of the thin-edged box diamond input amps - see the foot of the .

Serial number 1217 - currently in the UK (collection: Mike Handley)

Logo composed of separate letters - V O X - as in the amp above. Also as above, four-pin Cannon mains input and three-pin output sockets. Warning plaque centred.

Images of the amp from ebay sale, August 2015. Below images of the amp sold again in 2017:

Serial number 1220 - currently in the USA

Image from J. Elyea, Vox Amplifiers, p. 128. Note the logo, composed of separate letters V O X, as in the case of the amps above and below.

Serial number unknown - currently in Germany

A beautiful AC50 and early T60 cab - note the separate letters of the logo on the amp, and the "barred" O (a sort of theta) on the cab's logo. The amp is currently (August 2012) for sale - see Thanks to Jorn.

Serial number unknown - currently in Japan

Just this picture - originally . A beautiful set, both amp and cab with BASS logos.

Serial number unknown - currently in the USA

One of the few amps to have retained its "BASS" legend. Note the Cannon ITT-32 mains connector on the back panel. Warning plaque centred.

Serial number unknown - currently in Australia

A handsome AC50 in an AC100 box. The photos above show the amp in 2011. The pictures below show the present, restored state. Thanks to Guy for the images. The amp now has a new OT and circuit-correct capacitors. Note the distinctive shield underneath the input sockets. The treble and bass pots have the code "BL" = February 1964.

The volume pot has the code GM = July 1965, probably a factory replacement, along with the Wima coupling cap.

Serial number 1232 - currently in Australia

An AC50 in excellent condition. The volume pot has the code "DL" = April 1964; treble and bass pots "BL" = February 1964. One piece VOX logo. The third but last picture shows the amp in its restored state. Thanks to Guy for the new images.

Serial number 1244 - currently in the UK

No pictures, but discussed on an old Vox Talks thread - . Copper panel, diamond inputs, grille cloth replaced, signs of a previous replacement handle, renewed corner protectors. Amp serviced by Eric Snowball of ESE Music, who replaced the Bulgin connector with a modern IE receptable. ES also serviced the amp near the top of this page.

Serial number unknown - currently in the USA

Another nice amp belonging to North Coast Music.

Serial number unknown - currently in Europe

Good condition. Original connectors - mains and single output - on backboard. White warning plaque centred. Thanks to Julien for the images.

Serial number unknown - currently in the UK (?)

Old pictures from an ebay auction. A replaced handle, some new connectors on the back panel, and a blanked-off voltage selector.

Serial number 1312 - currently in Australia

Sold on ebay in 2014. A nice AC50, apparently untouched electronically. Small output transformer.

Serial number 1326 - whereabouts unknown

Sold on ebay in 2006. Complete with its original maroon (?) cover. Double speaker outputs. White warning plaque off to side.

Serial number 1387 - whereabouts unknown

Reported by J. Elyea.


The amps below are probably the last of the diamond input units, produced in parallel at Triumph with the new twin channel AC50s (both small and large box). For early large box AC50s in brown grille cloth, see this page.

Serial number 1532 - currently in the UK

Sold on ebay in 2006 (seller in Falkirk, Scotland). Amp and cab are in full working order. The latter is designated LFA52, serial number 11296. Thanks to Laurence for the info.

Wonderful original condition is evident from the pictures. The speaker cab is probably a very early solid state Foundation Bass cab - the driver is a Celestion T1296 (first logged in the Celestion record book in October 1966), there is a port underneath, and the baffle screws have been sealed with yellow paint (a typically later practice). The logo however is still of the old style, so this is probably a transitional unit between the valve and solid state lines.

Serial number unknown - currently in France

A splendid amp and cab set possibly with original black cloth.

Serial number unknown - currently in the USA

Sold on ebay in 2005. Probably the original black grille cloth, tired and sagging. Two sets of pics, the second showing the amp restored to full working order, and converted to two inputs by the provision of a repro control panel (the two other holes for input jacks blanked off by it). Thanks to Glen for info on this amp.