LARGE BOX AC50s - SOLID STATE RECTIFIED

mid to late 1965

Serial numbers in the 3000s.

The AC50s on this page are all solid state rectified - AC50 Mark 3s - conforming to schematic OS/072, a copy of which .

A few were built at Triumph, but the Vox/Burndept Electronics factory at Erith produced the bulk - ever increasing numbers to keep pace with orders from around the world, the USA in particular.

Often in AC50s destined for the American market, there is an extra capacitor not marked on the schematic - a grey Radiospares 0.05uf 500v in parallel with the "hot" side of the mains switch. So too for T60s and AC100s. Many have since been removed, but the tell-tale bracket remains.

During the course of production various changes took place. Externally, the warning plaque changed from white to red at around serial number 3800. In AC100s the new plaque marked the introduction of the brimistor. Perhaps it was meant to do the same for AC50s too, though the correspondence is not quite as neat as it is for the 100s.

Also worth noting that Burndept always stamped its chassis with serial numbers - on the aluminium flat of the preamp underneath the jack sockets.

Above, a rare mistake. These numbers do not correspond, however, to any sequence of assembly or registration. Unpopulated chassis, already with numbers, were simply kept in piles in no particular order. The nearest one was grabbed when a new amp was to be made.

One can see various examples of these stamped numbers below and on . Triumph chassis are always unstamped.

At around serial no. 3500, round Amphenol XLR speaker connectors become standard - four-pin Amphenol connectors had already been adopted for the mains cable.

Serial number plates remain two-line, and are fully machine-stamped.

The speakers in the 2x12" guitar cabs are generally always Fanes; the 18" units in the Foundation Bass cabs normally Goodmans Audiom 91s, black label, 15 ohm, 50W handling, though now and again Fanes occur.

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

Serial number 3013 - currently in the USA

Voltage selector set to 115V. Excellent condition. XLRs replaced by jack sockets; the three holes for the fixing of the 4-pin Amphenol mains socket still visible on the back panel.

Serial number 3087 - whereabouts unknown

Sold on ebay in late 2012. A fine-looking rig. Cover for the amp still present. Note the Fane speakers in the cab.

Serial number 3088 - currently in the USA

This is actually a valve rectified amp. For further pictures, see here.

Serial number probably in the low or mid 3000s - whereabouts unknown

Chassis number 797.

Serial number 3228 - currently in the USA

No internal shots, but good ones of the cab. The shininess of the transformers (seen through the grille) suggest production by Triumph. In the cab, a transverse cut-out in the baffle, possibly to aid the re-orientation of the Midax horn (for some reason). The drivers are the original Fanes.

Serial number 3260 - currently in the USA

Produced by Triumph - note the transformers and mustard capacitors. The amp has an added capacitor in line with the mains switch and fuse for the US market. Unfortunately the pics are just too small to make out date codes on the mustard caps.

Serial number 3276 - currently in Europe

A great Foundation Bass rig. Superb condition.

Serial number 3305 - currently in Europe

Serial number 3333 - currently in Europe

Chassis no. 0059. A new mains transformer and fuse holder; some capacitors replaced. Good to see the original connectors in place: rectangular Cannon XLRs for speakers out; Amphenol four-pin for the mains. Assembled by Burndept.

Serial number 3364 - currently in Europe

Produced by Triumph - note the mustard capacitors and lack of chassis number.

Serial number 3384 - currently in the USA

A Triumph-made amp. The cab has a new solid back and US Celestion speakers, perhaps from a Super Beatle. Midax horn and original wiring still in place.

Serial number 3385 - currently in the UK

Made by Burndept, in contrast to the amp above with serial no. 3384, which was made by Triumph. The chassis number is mis-stamped 00404, then redone as 00507. Possibly someone failed to advance the counter on the stamping machine. A similar mis-stamping exists on an AC100. The serial number on the back plate is hand-stamped, however, and a "N" has been added, which would signify "Normal" if the amp were an AC30.

The amp was service three times in the late 70s: some new capacitors, a new set of preamp valve holders, a number of pots; and the bypassing of the voltage selector.

The latest pot code is "DM" = April 1965. The mains transformer is an old replacement. Nobles Music in Cardiff .

Serial number 3412 - currently in the UK

Serial number 3437 - currently in the Netherlands

Pictures originally .

HEREON, ROUND AMPHENOL CONNECTORS USED FOR SPEAKER OUTLETS, SUPERCEDING THE RECTANGULAR CANNONS OR JACK SOCKETS

Serial number 3466 - currently in Norway

The amp has been modified, but appears originally to have been solid state rectified and assembled on a chassis designed for a valve rectifier (position now occupied by a filer cap.). Pot codes are DM, EM and GM = April, May and July 1965. Thanks to Fredrik for the pictures.

Serial number 3490 - currently in the UK

A great set, with original roller troller. Note the Amphenol XLRs all round.

Serial number 3491 - currently in the UK

Serial number 3506 - currently in Germany

Serial number 3521 - currently in the USA

Serial number 3529 - currently in the USA

Serial number 3539 - currently in the UK

A great original Foundation Bass pair.

Serial number 35xx - currently in Germany

Accompanied by two Foundation Bass cabs. The set .

Serial number probably in the mid 3000s - currently in Europe

Chassis number 1052. A nice Foundation Bass rig, new grille cloth, but otherwise in good condition.

Serial number unknown

Fitted with a reverb unit. Image originally posted here.

Serial number unknown - whereabouts unknown

Pictures probably from ebay. Sitting on an AC30 cab and trolley. Original back panel connectors in place. Note the reverb unit, as in the amp immediately above.

Serial number 3604 - currently in Germany

A great rig. The logo on the cab V O X in single letters. Still the white warning plaque. A couple of jack sockets added, and an IEC power connector. The castors on the trolley are also replacements. Note the speakers in the cab: very early Celestion ceramics - T1217s.

Further pics of the same amp

Serial number 3615 - currently in the USA

Assembled by Burndept - note the WIMA capacitors in the preamp. Round Amphenol speaker XLRs; white warning plaque. Good all-round condition. The amp was produced for export to the USA. In the last picture one can see the Radiospares suppressor capacitor added to AC50s destined for the States.

NEW

Serial number 3623 - currently in the USA

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A couple of jack sockets added on the back panel, otherwise in good order externally.

Serial number 3674 - currently in the USA

A full rig, complete with original Amphenol speaker and mains cables. Fane speakers in the cab. Condition is exceptional. Thanks to Steven for the pictures.

Serial number 3680 - currently in the USA

Chassis number 828. Complete with its original Foundation Bass cab and cables; Amphenol XLRs; still the white warning plaque. A nice rig. Thanks to Roger for the pictures.

Serial number unknown - currently in the USA

Box a little rough, but the amp itself is fine. Made by Burndept - chassis number 934. Amphenol mains connector, and backplate drilled for Amphenol XLR speaker connectors (not the holes at angles). One of the preamp valves is "VOX" branded. The pots have date codes "GM" = July 1965. This amp has had a surgistor fitted up by the voltage selector at some Thomas Organ service centre.

Serial number 3687 - currently in the UK

This amp - a valve rectified chassis - is anomalous. In fact it has been reboxed in a box consonant with the serial number - note the sets of three holes for Amphenol XLR speaker connectors on the back panel plate. The chassis is also registered at the foot of .

Serial number unknown - currently in Germany

Solid state rectified. However, the box is an early one - note there is no hole for the mains connector. The plastic corners are perhaps repros - double pin, instead of the single pin of 1965. The round Amphenol XLR speaker connectors are likely to be new to the box (ie. replacements). The white warning plaque may belong to the early box, or to the box the amp originally belonged to. Pictures originally posted .

Serial number unknown - currently in Europe

The outlines of the round Amphenol XLRs are visible on the escutcheon plate. Assembled by Triumph.

Serial number unknown - currently in the USA

Machine stamped serial plate. Solid state rectified amp, probably in the mid 3000s. The link voltage selector is liable to be an addition/replacement. Fane speakers on a chipboard (particle board) baffle. The amp's handle has been replaced. No warning plaque.

Serial number unknown - currently in Japan

Paired with later solid state Foundation Bass cab (from 1967/68). The serial plate has probably been moved to cover the hole for the mains socket.

Serial number 3708 - currently in Japan

Amp and cab in great condition. Original mains and speaker cables present.

Serial number in the 3000s - currently in Europe

A good Foundation Bass set. Two-line serial number plate; warning plaque still white; and a pair of Amphenol XLRs for the speakers.

NEW

Serial number unknown - currently in the USA

White warning plaque, two-line serial number plate, and originally, Amphenol XLR speaker sockets (one can see the screw holes at angles. Otherwise no direct clue to serial number.

NOTE THAT THE AMPS BELOW REGULARLY HAVE THE NEW-STYLE RED WARNING PLAQUE

Serial plates two-line and for the first time, three-line

Serial number 3814 - whereabouts unknown

Chassis number 910. The pots have codes "EM" and "GM", respectively May and July 1965. Shop sold, 2012?

Serial number 3846 - whereabouts unknown

Some knobs missing, but otherwise (cosmetically) fine. Sold by Heritage Auctions in late 2012 - pictures from .

Serial number 38xx - currently in the UK

No picture of the front unfortunately. Note the replacement metal corner protectors.

Serial number 3905

A late instance of the white warning plaque (in a non-standard position).

Serial number 3945 - currently in the USA

Serial number 3969 - currently in Europe

Great condition. Original mains and speaker cables still extant.

Serial number 3980 - currently in Europe

Serial number unknown - currently in the USA?

Chassis number 999.

Serial number unknown - currently in the USA?

Sold on ebay US in September 2012. Chassis number 872. Pot codes in the preamp are "GM" = July 1965.