The Vox AC50 mark 4 (Mk IV); surviving examples of large box, solid state rectified, twin channel amplifiers, serial numbers in the 8000s. Produced in 1967 and 1968.

Valve rectified amps > Solid state rectified AC50s, 1967-68 > serial numbers in the 8000s

LARGE BOX AC50s - SOLID STATE RECTIFIED

AC50 Mark 4 (Mk IV)

Serial numbers in the 8000s - 1967 and 1968

Amps assembled at the Vox Works / Burndept factory (always the presence of the stamped chassis number). American-style logos.

The band "influention" with a late large box AC50 (note the logo) on top of a Super Foundation Bass speaker cabinet.

The external characteristics of these amps are much as serial numbers 7400-7999: American style logo at front, two-pin corner protectors, Amphenol connectors on the back panel. The only major difference is the regular appearance now of the white warning plaque.

Internally: amps begin to have more and more components used in the solid state amps: yellow Dubillier coupling caps in the preamp, and small Radiospares potentiometers. CCL capacitors had already been brought in by around serial number 7400.

The Mark 4 schematic gives an ECC83 for V1 (though one could always substitute a good balanced ECC83 for the ECC82 in a Mark 3 amp) and a new topology for V3 - the phase inverter now "long-tailed". It is also worth noting that cathode bypass caps are dropped for the preamp valves (V1 and V2).

One can spot a Mark 4 amp by the presence of a 2.7K resistor in the first position (left-hand side) on the preamp tagboard. Mark 3 amps have 4.7K.

Vox AC50 Mark 4 schematic. Click for a larger image, as ever.

Above details from serial no. 8168. First pic showing one of the small pots in the preamp (the same type as in the early solid state amps). The second pic showing two of the yellow Dubillier caps. For examples of the Vox solid state amps, see for instance this page.

1968

By serial number 8168, however, we are already well into 1968: the CCL filter capacitors are dated "B8" = February 1968. An outline of the CCL codes is given here.

In the left-hand capacitor, one can only see the name "CCL". At right though, we have the date code "B8".

These late amps were produced close to the end of Jennings Musical Industries (in mid 1968). For the emergence of "Vox Sound Equipment Limited" (VSEL), which took over from JMI, see this page on the Vox Supreme website. AC50s issued by "Vox Sound Equipment Limited" are registered here.

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

Serial number 8030 - currently in Europe

Grille cloth and vinyl covering removed. All cabinet fittings still in place. Dubilier polypropylene capacitors in the preamp. The choke has the code "EFM".

Serial number 8043 - currently in Europe

Regrilled in brown cloth and a new logo added.

Serial number 8044 - currently in Europe

Hand-stamped serial number plate. A Foundation Bass set (as the majority of amps on this page probably were).

Serial number 8063 - whereabouts unknown

Serial number 8071 - currently in France

Chassis number 4119. An AC50 Mark IV and Defiant cab set. The chrome tongues on top of the speaker cabinet slide into the the mounting brackets on the underside of the amplifier section (much as a Defiant) to secure the amp to the cab's top. See this page on the Vox Supreme website for further examples. There are doubled-up red CCL capacitors in the power section, and yellow polypropylene Dubilier capacitors (as used in the Vox solid state range) in the preamp. The mains transformer has two codes stamped in white: "EFM" (?), the other unreadable. The choke also has two codes stamped on it: "EFW" and "LDC". Speakers are probably ceramic Celestion T1297s. Thanks to Francis for the pictures.

Serial number 8091 or 8097 - currently in Europe

Serial number 8106 - currently in the USA

Serial number 8108 - currently in Europe

Serial number 8110 - currently in the UK

Chassis number 4118. Red CCL main filter capacitors in both power section and preamp.

Serial number in the 8000s - currently in the UK

No serial number, but chassis number 4076. The date codes of the two red CCL in the preamp are "C7" and "L6" = March 1967 and December 1966. As in the case of amps on this page, there are no cathode bypass capacitors for the preamp valves. Pot codes are "EN" and "FN" (May and June 1966).

Serial number in the 8118 - currently in the UK

The back panel slightly rejigged, but otherwise in good order. The serial plate still states "Vox Amplifier". Pictured with a Vox 2 x 15" cab from late 1964. For other early examples of what was later called the T100, see this page. Thanks to Matt for the pictures. Amp and cab may soon be for sale.

Serial number 8134 - currently in Belgium

The plate is currently attached to a 1970s AC30. Thanks to Wouter for the picture.

Serial number in the 8000s - currently in Europe

Three-line hande-stamped serial number plate, "VOX AMPLIFIER" at its head. Originally sold by Musik-Crusius in Darmstadt. The amp still has its original cover.

Serial number unknown

Three-line hande-stamped serial number plate, "VOX AMPLIFIER" at its head. One of the red CCL capacitors has the date code "F7" = June 1967.

NEW

Serial number 8143 - currently in Europe

Chassis number 04379. Original transformers and choke in plate. In the preamp, Mullard mustard signal capacitors. The amp is currently (April 2024) up for sale on Reverb.

From this point serial number plates are headed "AMPLIFIER" rather than "VOX AMPLIFIER"

Serial number 8149 - currently in Europe

New-style horizontal logo; "AMPLIFIER" at the head of the serial number plate. Model designation and number machine stamped.

Serial number 8153 - currently in Europe

Chassis number looks like 42xx. A replaced output transformer but otherwise in good original condition. The brimistor is still in place. The bias potentiometers are of the type used in the Vox solid state amps.

Serial number 8158 - currently in Europe

New-style horizontal logo; "AMPLIFIER" at the head of the serial number plate. Model designation and number machine stamped.

Serial number 8168 - currently in the USA

Chassis no. 4232. The CCL filter cap has the date code "B8" = February 1968. The preamp has yellow Dubillier capacitors and metal fixing plates for the pots (both found in Vox solid state amps).

Serial number 8170 - currently in Europe

Paired with a reproduction AC50 Super Twin cabinet containing new Celestion gold speakers.

Serial number 8184 - currently in Germany

Horizontal logo. "AMPLIFIER" at the head of the serial number plate. No further details at present.

Serial number in the 8100s / 8200s - currently in Holland

A late AC50, serial number in the 8100s or 8200s. White warning plaque on the back panel, serial number plate stating "AMPLIFIER" rather than "VOX AMPLIFIER". The preamp has been recapped. Servaas Muziekhandel in The Hague was a major outlet for Vox in the Low Countries in the mid to late 1960s - see this page.

Serial number in the 8000s

This amp is here because it has no cathode bypass caps. Amps with numbers in the 7000s seem to have them. Note the presence of the doubled up red CCL main filter caps on the upper chassis.

Serial number unknown

Chassis no. 4071. No serial number plate, so the amp's position here is not absolutely certain. However, in company with the amp above, number 8178, there are no cathode bypass caps in the preamp. The pots have the date code "EN" = May 1966. Thanks to Misha for the pictures.

Serial number 8178 - currently in Germany

Very probably issued with the solid state Foundation Bass cab which accompanies it.

Serial number 8196 - currently in Europe

Serial number 8200 - currently in Europe

Originally sold by Servaas Muziekhandel in The Hague

Serial number 8209 - currently in Germany

One of a number of late AC50s exported to countries in northern Europe.

Serial number 8211 (or 8231?) - currently in Europe

Serial number 8215 - currently in the USA

Serial number 8219 - currently in the USA

Chassis no. 3422. New grille cloth and replaced logo.

Serial number 8221 - currently in Europe

Thanks to Heimz for the pictures.

Serial 8224 - currently in the UK

Chassis no. 4298. Issued with a new-style solid state Foundation Bass cabinet. The green CCL filter caps have the date code "G7" = August 1967. In the preamp, miniature pots (as used in the solid state range) and Mullard mustard capacitors.

Serial number 8234 - currently in Finland

Thanks to Jorma for details of its existence.

Serial number 8270 - currently in the UK

Chassis number 4374. Dormant for some years, the amp has been has been expertly restored. Note that the paper labels on the undersides of the transformers have inspection stamps. The bias pots between the EL34 power valves are of the type used in the Vox solid state amps. Thanks to Rich for pictures and details.

Serial number 8277 - currently in the UK