Thick-edged box; copper control panel; diamond inputs

Probably around 200-250 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 affixed) and boxes provided.

Serial numbers are therefore not always 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.

Amps were issued initially with Foundation Bass speaker cabinets or closed back AC30 "extension" cabs, as in the picture below:

The Migil 5 on the Morecambe and Wise Show, Saturday 27th June, 1964, 8.25pm, with a thick-edged small-box AC50.

From July / August 1964, AC50s for guitar were paired with the new large box AC50 speaker cabinet measuring 33" x 23" x 11". This contained two 12" Celestion silver alnico drivers (T1088) and a Goodmans Midax horn. On the Midax, .

Click as ever for a larger image. Jennings Musical Industries catalogue, August 1964. The AC50 is drawn with a thick-edged box. The trolley is still of the very earliest type.

Abbey Road, Studio 2, July/August 1964. The AC50 belonging to Tony Hicks of The Hollies. Recording session for the album "In the Hollies Style", released in November '64. The number of diamonds on the grille cloth shows this is a large box AC50 speaker cabinet.

Below the image of the AC50 Super Twin in the Jennings "Precision in Sound" newspaper-format catalogue from late 1964. The drawing, as in the catalogue from August 1964 above, shows an AC50 in a small thick-edged box, but its dimensions are those of the new large-box AC50.

Detail from the Jennings "Precision in Sound" catalogue.

Adverts and promotional material issued by Jennings Musical Industries for the AC50 are being collected together .

GENERAL CHARACTERISTICS

Single channel; four inputs arranged in a diamond formation; still the GZ34 rectifier valve; copper control panel; and link voltage connector. The metal grille at top of back panel instead of the bottom (as in the earliest AC50s). There are 6 holes in the chassis plinth for each transformer, allowing units with centre as well as corner fixings to be fitted. The aluminium preamp chassis has slots rather than simple holes so that transformers of different heights could be used.

Output transformers are generally of a fairly low profile; but one sometimes finds the older taller type (as used in first generation AC50s in thin-edged boxes).

On the back panels, mains sockets are generally bakelite Bulgins at first, then later on Cannon LNE-32s; speaker sockets are rectangular Cannon XLR-3-32s.

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.

DIAMOND INPUT AMPS IN THIN-EDGED BOXES

Serial number 1101. Current whereabouts unknown.

Whether the amp (and its Foundation Bass cab) still survives is unknown. The Guarantee Card supplied by Vox does however.

"4/1101" presumably indicates that the amp had four inputs. Its box is likely to have been thin edged.

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 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 inspire 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

The "AC50 Super Twin": the amplifier in a thick-edged box, and the speaker cabinet 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 unknown - currently in the UK

  • diamond input ac50 in early box
  • diamond input ac50 in early box
  • diamond input ac50 in early box
  • diamond input ac50 in early box
  • diamond input ac50 in early box
  • diamond input ac50 in early box
  • diamond input ac50 in early box
  • diamond input ac50 in early box
  • diamond input ac50 in early box
  • diamond input ac50 in early box
  • diamond input ac50 in early box
  • diamond input ac50 in early box

Amp in excellent condition, box in course of light restoration. Tolexing had covered the groove for gold string at rear. The black grille cloth a later replacement. Two speaker outputs originally? White warning plaque originally centred. The four inputs on this amp are in parallel. The input sockets, as in the case of the amp with the black panel, are made by the Rendar Company. Possibly a two-holer originally converted (at factory?) into four? The pots have the code "BL" = February 1964. As in the case of other early AC50s, the treble and bass pots are linear instead of logarithmic (as specified in the schematic). Thanks to Stu for the images.

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

Another diamond input amp in a thin edged box. No other details available at present.

SMOOTH GREY TOLEX

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.

BASKETWEAVE TOLEX

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.

NEW

Serial number 1207 - currently in Denmark

Some replaced components in the preamp but neatly done. The power amp is in good original order. Pot codes are "BL" = February 1964. Thanks to Solus for the pictures.

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.

BLACK GRILLE CLOTH

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.