LARGE BOX AC50s - SOLID STATE RECTIFIED
AC50 Mark 3 (Mk III)
Serial numbers in the 6000s - later 1966
Serial number 6023
The amps on this page were, in the main, assembled at the Vox Works / Burndept factory in Erith - note the presence of the stamped chassis number. There is nothing to indicate that Triumph Electronics, a principal contractor, was building many AC50s for Vox at this point. Triumph had the 7 series amps (among other things) on its plate for the better part of 1966.
Large numbers of Foundation Bass and Super Twin sets continued to be exported to the States, Europe and elsewhere.
The brimistor is the norm. Transformers are the black-topped units made by the company that produced the transformers for AC100 mark 2s, and later on, the Vox solid state amps. These came in at around serial number 5600 - see the previous page.
The warning plaque is red, and the serial number plate is three-line.
Red Lemco capacitors, which first make their appearance around serial number 5739, persist in the preamp until around serial number 6300 (see below). Blue Hunts cathode bypass caps follow in step.
For the most part the main filter capacitors are Hunts (blue) and TCC = Telegraph Condenser Company (green, sometimes gold). Few Hunts dates codes are visible in the existing pictures unfortunately as the clamps obscure the relevant parts of the printed legends.
Speakers in the Foundation Bass cabs are either Goodmans Audiom 91s, or Celestion T1279s. Fane 122/17s (15ohms, 25watts handling) were generally used in the guitar speaker cabinets, though one occasionally finds Goodmans 241s.
See for instance the speaker cabinet on this page. Goodmans 241s are excellent speakers, but they were evidently more expensive than Fanes.
Below, a register of amps. If anyone knows of others that have not yet been included, as ever do let me know.
Serial number 6010 - currently in Germany
A Foundation Bass set, complete with original covers. The brimistor has been replaced with a resistor. The speaker cabinet has its original Goodmans Audiom 91 driver. The name of the shop (on the plaque on top of the amplifier section) that originally sold the AC50 is not known at present.
Serial number 6018 - currently in the UK
Control panel has faded in places to green, as is the case with a number of other later AC50s. Where the paint is lost completely the brass underlayer is showing through.
Serial number 6023 - currently in the UK
Chassis number 2634. Pot codes are "AN" and "EN", respectively January and May 1966. Note the presence in the preamp of red Lemco capacitors.
Serial number 6028 - currently in Japan
Chassis number 2505. Again, red Lemco capacitors in the preamp. One of the pots has the date code "EN" = May 1966. The choke (part no. 66524) has the code "ILB". Thanks to Kenichirou Fujimura for info on this amp.
Serial number 6090 - currently in Germany
Serial number 6100 - currently in Belgium
Serial number 6106 - currently in the Netherlands
Pots have the date code "AM" = January 1966. Note that the mains transformer is of the older type - i.e. plain metal rather black shroud. The chassis is likely to have been assembled by Triumph - the grommets for the pass-through holes are distinctively orange in colour. Thanks to Rob for the pictures.
Serial number 6107 - currently in Europe
Chassis no. 2659.
Serial number 6115 - currently in Europe
Serial number 6150 - currently in Europe
As in the case of the amp above (no. 6115), the serial number plate has been moved to cover the hole for the mains socket. This amp has, unusually, a white warning plaque.
Serial number 6168 - currently in Australia
Bought in Manchester in 2001, now in Tasmania. Thanks to Steve for the pictures.
Serial number 6171 - currently in the USA
Serial number 6172 - currently in Europe
Serial number 6234 - currently in the USA
Serial number 6238 - currently in Sweden
Chassis 2561. Repaired in Goteborg in 1976. A complement of green Plessey (?) filter capacitors added on the upper chassis, along with a fan. A red warning plaque, in Swedish, probably supplied early on, can be in the last picture. I think the text is something along the lines of "Make sure the device is unplugged from the mains before removing the back panel".
Serial number 6253 - currently in the USA
Chassis 2911. Pot codes are "FN" = June 1966. Pictures kindly supplied by Tom along with the history:
"My friend's dad bought it new and used it for his Fender Rhodes Piano. He bought the Head, 2-12" guitar cab, and 1-18" Foundation Bass cab. He stopped using it sometime in the early 80s when it was put in his attic.
"November 2010, friends dad was cleaning out his attic and asked me if I wanted the rig. I said sure and asked how much money he wanted for it. He stated he wanted nothing for it, just simply wanted it out of his attic. I took it home and cosmetically it was in rough shape. At some point the grille cloth was replaced with carpet! It was filthy. I was surprised it worked! One of the 12" speakers had been replaced with what I believe to be a Jenson, the other appeared to be a Goodmans 12" that I believe to be original. Only the Jensen was working...barely. The Goodmans Midax horn was in the cabinet, however not working. I took the head to a Valve Amp repair shop in my area. Had it cleaned internally, retubed, and biased. It needed a couple caps replaced but otherwise was in great condition."
"I ended up putting 2 new Jensen 12" speakers in the cabinet with the horn, but left the horn disconnected. The Foundation Bass cabinet still has its original Celestion 18" in it. It was in pristine condition inside once I opened the cabinet up...everything was like new!"
Serial number 6281 - currently in Europe
Voltage selector removed. The same red information plate as added in Sweden to serial number 6238.
Serial number 6298 - currently in Europe
Grille cloth faded to brown (as sometimes happens). Nice amp.
Serial number in the 6000s - currently in Europe
Chassis number 2718. A new mounting plate for the XLRs has been provided on the back panel (necessitating the moving of the warning plaque). Original blue Hunts capacitors still in place in the preamp. The cab is an AC30 cab in an original early Super Twin trolley - note the basket top for the amp.
Serial number 6341 - currently in Australia
Thanks to Adrian for the pictures
Double-pin corners first come in at around this point
Note, however, that a good number of amps that follow still have single-pin corners. It is not until we get into the high 6000s - in the 6800s so far as one can tell at present - that double-pin corners become the norm. Bins of old ones and new ones were evidently used side by side for some time, ie. until the old single-pin ones had run out.
Serial number 6355 - currently in the UK
Visible date codes: the TCC or Plessey 4uf bias capacitors "XE" = May 1966. Pots have "FN" = June 1966.
Serial number 6375 - currently in Europe
Serial number 6471 - currently in Belgium
Serial number in the 6000s - currently in Europe
Serial number in the 6000s - whereabouts unknown
Serial number in the 6000s - currently in the UK
The amp has corner protectors with double pins; red warning plaque, and Amphenol mains socket. The speaker cab, with Celestion alnico T1088s rather than Fanes, may have belonged originally to another, earlier amp. But difficult to say without evidence of date codes and so on. The socket on the cab is an Amphenol rather than a Cannon.
Serial number 6474 - currently in Germany
Chassis no. 3001. A replaced mains transformer, but otherwise in great condition.
Serial number 6552 - currently in the UK
Serial number 661x - currently in Europe
Serial number 6670 - currently in Europe
Serial number 6680 - currently in the UK
Below, pictures from the sale of the amp - note the black shrouded transformers and the original Hunts capacitors.
Serial number 6685 - currently in Holland
Thanks to Arnaud for the pictures.
Serial number 6690 - currently in the UK
Serial number 6722 - currently in Germany
Currently (October 2020) here.
Serial number 6757 - currently in Italy
Accompanied by its Foundation Bass speaker cab (with Celestion T1108). Red Lemco capacitors in the preamp. Note the inspection tags - one at the mains switch end of the preamp board, the other at the rectifier end of the power section board.
Serial number 6760 - currently in the USA
Thanks to Gene for the note on the existence of this amp.
Serial number 6798 - currently in the UK
Accompanying a 1980s V125 cab.
Serial number 6808 - currently in the UK
Another with a V125 cab.
Serial number 6824 - currently in Europe
A Foundation Bass rig.
Serial number 6856 - currently in Europe
Chassis number 2951. Red Lemco capacitors in the preamp, along with grey Radiospares polypropylene. The panel is a later replacement (JMI did not mark inputs "Hi" and "Lo".
Serial number 6884 - currently in Europe
Accompanied by a solid state Vox Sound Equipment Ltd. Foundation Bass cab. Probably exported originally to Germany or the Low Countries - a metal shop badge (rare in England and the US) can be seen on the top front edge of the speaker cab.
Serial number 6911 - currently in Europe
Serial number 6919 - currently in the UK
In good order, some capacitors renewed (as one might expect). One of the original red CCL filter caps in the preamp has "K6" = November 1966; the light blue Hunts caps in the preamp "UYA" - which should mean the 9th week of 1966.
Serial number 6925 - currently in the USA