LARGE BOX AC50s - SOLID STATE RECTIFIED

late 1966 and 1967

Serial numbers in the 7000s

Amps assembled primarily at the Burndept factory (note the presence of the stamped chassis number).

The amps follow the pattern of previous batches - for AC50s with serial numbers in the 6000s.

EXTERNALLY: the red warning plaque, the three-line serial number plate, Amphenol connectors on the back panel, and corner protectors with two pins (nails) instead of one.

From around serial number 7400, the new American style logo comes in. It is also to be found on the Vox solid state amps, which were finally brought to market in April 1967. For AC50s, this may signal 1967.

INTERNALLY: at first blue Hunts capacitors are used in both preamp and power amp. Then, around serial number 7400 the main preamp filter caps become red or plain CCL. CCL (Cambridge Capacitors Limited, later taken over by Pye) was also used for the Vox solid state amps - the Conqueror, Defiant, Supreme et al. - from early 1967. Visible date codes on this page are from December 1966. For a note on how to decipher these codes,

The main filter caps on the upper chassis (just behind the main power valves), on the other hand, are green Plesseys at first - see nos 7419, 7519 and 7722 below - and doubled up. This "doubling up" corresponds with the doubling up of main filter caps in the AC100 (the AC100/4) in 1967. Some AC50s at this point - ie. after serial number 7400 - retain the old arrangement of only two caps (normally red CCLs), however.

Note too that as time goes on cathode bypass capacitors for the preamp valves - the small blue Hunts caps in the left-hand half of the tagboard - are phased out. Apparently those for V1 first, then V2.

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

Serial number 7120 - currently in Europe

Voltage selector omitted for the Scandinavian market.

Serial number 7144 - whereabouts unknown

Serial number 7150 - currently in the UK

Sold on ebay.com some time ago - voltage selector set to 115v. Excellent condition. The speakers (Jensens) are later replacements; and the back panel - a solid piece with a cut-out - is probably a replacement too.

Serial number 7214 (?) - currently in Italy?

A single pic. Said to be serial no. 7214.

Serial number 72xx - currently in the UK

Pictured with its speaker cab - note the circular port on the cab's back.

Serial number 7293 - currently in Belgium

Reasonably good condition. A jack socket added on the back along with an IEC mains socket.

Serial number 7311 - whereabouts unknown

Just the serial number plate for the time being.

Serial number 7320 - whereabouts unknown

From this point the new American-style logo

Note that the warning plaque on the amps that follow is generally white. From this point certainly red CCL filter capacitors come in, along with yellow Dubillier signal caps.

Serial number 7419 - currently in Scandinavia

Serial number in the 7000s - currently in Denmark

Chassis number 3963. No pictures of the box or logo unfortunately.

Serial number 7591 - currently in Europe

Chassis no. 4572. Note the double row of capacitors on the upper chassis. Some of the pots and capacitors are of the type used in Vox solid state amps. The red CCL preamp filter capacitor has the date code "L6" = December 1966.

Serial number 7722 - currently in Europe

Chassis number stamped as 14682, ie. 4682. Accompanied by its original cab, constructed in the same manner as the Foundation Bass cabs issued with the solid state range - a port at bottom and a backboard fixed with many more screws.

The amps below have (or had) blue Hunts cathode bypass caps in the preamp

NEW

Serial number in the 7000s - whereabouts unknown

Still the old-style VOX logo, as in the case of the amp below. Chassis no. 3248. The date codes of the pots are tantalisingly indistinct - "FN" ? - which would be June 1966. No shot of the back panel unfortunately.

Serial number in the 7000s / 8000s - currently in Europe

Probably new grille cloth, logo, and piping (note its whiteness). Red CCL filter caps, yellow Dubilliers, and the small pots used in the Vox solid state amps. Cathode bypass caps are present for both V1 and V2 in the preamp (the original blue Hunts for V2).

Serial number in the 7000s / 8000s - currently in Europe

Chassis 3570. The red CCL filter capacitors have the date code "K6" = November 1966. The green TCC caps on the underchassis have "XH" = August 1966; and the pots have "JN" = October 1966. The original blue Hunts cathode bypass capacitors are still in place in the preamp. The mustards may be replacements for the yellow Dubilliers.

Serial number in the 7000s / 8000s - currently in Europe

Chassis 3xx6. Pot codes "IN" and "JN" = September and October 1966. The choke is stamped 26 Sept. Yellow Dubillier coupling caps in the preamp.

Serial number in the 7000s / 8000s - currently in Europe

Two rows of main filter capacitors (as 7591 above). In this case they are likely to be red CCLs rather than green Plessey. There are cathode bypass caps in the preamp, but not blue Hunts. A hole has been punched through the serial number plate, which still has "Vox Amplifier" rather than "Amplifier" alone.