LARGE BOX AC50s - SOLID STATE RECTIFIED
AC50 Mark 3 (Mk III) and the first Mark 4s (IV)
Serial numbers in the 7000s - late 1966 and 1967
Vox advert for the AC50 in the solid state catalogue of early summer 1967. Click as ever for a larger image.
Amps assembled primarily at the Vox Works / Burndept factory (note the presence of the stamped chassis number).
The amps initially follow the pattern of previous batches of Mark 3s- see this page for AC50s with serial numbers in the 6000s.
With serial number 7591, we see the first AC50 Mark 4 - built according to schematic OS/163 - see further on the next page.
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, see this page on the Vox Supreme website.
A number of amps have doubled-up filter caps on the upper chassis (just behind the main power valves), a feature of the Mark 4 schematic, green Plesseys at first - see nos 7419, 7519 and 7722 below. This "doubling up" corresponds with the doubling up of main filter caps in the AC100 (the so-called 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.
One way of differentiating a Mark 3 amp from a Mark 4 is the number of capacitors on the far right-hand side of the preamp tagboard. Mark 3s have three caps, Mark 4s have two.
Note too that in AC50 mark 4s 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 do let me know.
Serial number 7014 - currently in Europe
Paired with an AC30 cab
Serial number 7027 - currently in the UK
A Foundation Bass set in full working order. The back panel of the speaker cab has 3 screws down each side. Thanks to Marty for the picture.
NEW
Serial number 7035 - currently in the UK
Serial numbers 7035 and 7139.
Chassis number 3531. In the preamp, blue Hunts caps with date codes "UYA"" and "UWY" = 9th and 10th weeks of 1966 for their manufacture. The red CCL filter capacitors have "K6" = November 1966. In the speaker cabinet, Goodmans heavy-frame drivers (and heavy-duty wiring), indicating that the amp was produced for export. A similar cab can be seen on this page. Cone code 3012Y04-H1; Midax horn no. 19518. Thanks to Mark for the pictures.
Serial number 7073 - currently in Europe
Probably in Scandinavia as the voltage selector has been removed.
Serial number 7120 - currently in Europe
Voltage selector omitted for the Scandinavian market.
NEW
Serial number 7139 - currently in the UK
Serial numbers 7035 and 7139.
Chassis no. 3540. Inspected by Newcombe. In the preamp, the pots have "JN" and "KN" date codes = October and November 1966. The blue Hunts cathode bypass caps have "UWY" = 10th week of 1966; and the main CCL filter caps have "K6" = November '66. The speakers are Fane 122/17, 15 ohms, 25 watts apiece; Midax horn serial number 26100.
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 7158 - currently in Europe
Serial number 7214 - currently in Sweden
Serial no. 7214. Currently (March 2019) on Reverb.
Serial number 7237 - currently in the UK
From an electronic standpoint pretty much untouched.
Serial number 7247 - currently in the UK
Pictured with its speaker cab - note the circular port on the cab's back. The two CCL 16+16uf filter caps have the date code "L6" = December 1966. Thanks to Ian for the new pictures.
Serial number 7272 - currently in Scandinavia
Serial number 7293 - currently in Belgium
Reasonably good condition. A jack socket added on the back along with an IEC mains socket.
Serial number 7298 - currently in the Europe
Chassis number 3555. Original Hunts filter capacitors in the preamp (?). In common with amps of this period, the mains cable has been hard-wired and the serial number plate at right on the back panel.
New pictures
Serial number 7311 - whereabouts unknown
Just the serial number plate for the time being.
Serial number 7320 - whereabouts unknown
Serial number 7371 - currently in Germany
Chassis number 3799. Sold by Musikhaus Werner. Red CCL filter caps and blue Eries in preamp. Signal capacitors are yellow (0.022uf) and yellow and blue (0.1uf) Dubiliers, the first instance of the former in an AC50 so far. Dubilier caps were used in the Vox solid state range of amps (from Spring 1967). For other amps with blue Erie cathode bypass cas, see the group at the foot of this page.
Serial number 7380 - currently in the UK
An unusual plate - seems genuine: hand-stamped, the last digit of the serial number re-stamped, and a stray "3" in the rating panel.
Serial number 7385 - currently in the USA
Good external order, original fittings still present on the back panel. Thanks to Kit for the pictures.
From this point the new American-style logo
Sporadically at first. Also from this point, red CCL filter capacitors come in, along with yellow Dubillier signal caps. A little later, white warning plaques, normally found on amps with the new US-style logos.
Serial number 7406 - currently in Scandinavoa
Voltage selector removed (in accordance with local electrical legislation. Note the US-style VOX logo.
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 7430 - currently in Norway
Chassis no. 3852. Superb condition, the only changes being those the importer was required to make - removal of voltage selector, and the provision of ancillary fuses. The amp is similar to serial number 7444, below. The red CCL filter capacitors have the date code "L6" = December 1966. Pots have codes "JN" and "LN" = October and December 1966. The light blue Hunts bypass caps have "UWW" and "UWH" = 11th and 12th weeks of 1966. Thanks to Bjorn for the pictures.
Serial number 7444 - currently in Norway
In fine condition. The main preamp filter caps - red CCLs - have the date code "L6" = December 1966, so the amp is likely to have been made in early 1967. The blue Hunts caps have the date "UWH" = 12th week of 1966. Thanks to Bjorn for the pictures.
Serial number 7481 - currently in Europe
The original cover survives.
Serial number 7557 - currently in Europe
Serial number 7563 - currently in Europe
A relative high serial number for a box with an old-style logo.
Serial number unknown - currently in Scandinavia
Voltage selector replaced in conformity with Scandinavian legislation. In the preamp, light blue Erie resistors as in many of the amps below with American-style logos. The main preamp filter caps are red CCLs.
Serial number 7572 - currently in Europe
A Foundation Bass set, the amplifier section still with its original cover.
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 7595 - currently in the UK
Thanks to Martin, pictures coming shortly of PA50 serial number 7595 (all valve), early 1967. All PA50s had standard AC50 serial number plates with numbers in the same sequence.
Serial number 7597 - currently in Europe
PA50 number 7597 can be seen on this page - transistor front end, valve power section.
From this point serial numbers are hand stamped
Serial number 7701 - currently in the USA
Paired with a solid state Foundation Bass speaker cabinet - note the port at bottom. A similiar pairing below (serial no. 7722). Both are probably from the second quarter of 1967.
NEW
Serial number 7713 - currently in Europe
Hand-stamped serial number plate. In the preamp, yellow Lemco signal caps and large blue Dubiliers. Electrolytics are Hunts (25uf) and red CCLs.
Serial number 7719 - currently in the Netherlands
Paired with a "Vox Sound Limited" Foundation Bass speaker cabinet with Fane driver. Thanks to Joop for the pictures.
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.
Serial number in the high 7000s - currently in Europe
Serial number 7735 - currently in Europe
Serial number 7759 - currently in Europe
Sold originally by Servaas in Holland - shop plaque upper right on the front grille cloth. Good all round condition.
Serial number in the 7000s (?) - currently in Scandinavia
Red Lemco capacitors in the preamp; polythene (mixed dialetic) 0.1uf coupling capacitors; Hunts and TCC in the bias circuit. The blue Hunts caps can be seen in the fifth pic. The voltage selector has been removed to conform with Scandinavian legislation. In its place (supplied by Vox) is the hang-tag that came with the amp.
The amps below have or had light blue Hunts / Erie cathode bypass caps (with fine white script) in the preamp
Serial number in the 7000s - currently in Europe
Chassis number 4038. The light blue Erie capacitors have the date code "NYU" = 6th week of 1967. The original red CCL capacitors are in place. The code on the choke is not quite decipherable. The preamp pots are of the type used in the Vox solid state amps.
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.
