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2024
19th December
A few more pictures of AC50 serial number 1784, valve rectified, late 1964. Box, slider board, and back panel are all chalked "10" so that the three could be matched up in the event of separation. Screw holes and so on varied from cabinet to cabinet. The chances are that the back panel, say, of one would not match up with the main box of another.
Chassis power section: one bias resistor replaced, otherwise untouched. The bias pot has the date code "IL" = September 1964.
Steve Rolfe (the pencil monogram "SR"), who worked for Triumph from 1963 to 1966, set the bias at (-)36v. Assembly was signed off by Dave Earp ("DE"), who joined and left Triumph at much the same time as Steve.
The ink-stamped part number "105736" is still visible on the underside of the output transformer.
Chalked "10" on the baffle of the cabinet, as also on the inner face of the back panel and underside of the slider board.
18th December
Below, scarce these days, a three-pack of unused Mullard Xf2 EL34s from 1966, a pair and a spare. In the USA, RCA, General Electric, and others, supplied boxes (cartons) of five, a quad and a spare.
For the amps used by The Beatles, Mal Evans is likely to have had a carry-case of spare Mullard valves, probably multiple singles rather than packs.
One of the EL34s, with date code (as for the others) in May 1966.
10th December
Two new entries: thanks to Boris, one for AC50 serial number 4236, later 1965 (brimistor present), a Foundation Bass set; the other for AC50 serial number 1784, late 1964, further pictures to come.
1st November (2)
The entry below has been corrected. The date code of the second pot reads "BL" rather than "DL".
1st November
AC50 serial number 1028B: thanks to its new owner, pictures of the pot codes: "BL", "BL", and "GK", respectively February 1964, and July 1963 for their manufacture. The amp is likely to have been ready for sale in March.
Detail of AC50 serial number 1028B.
15th October
Recently come to light, AC50 serial number 1028, single channel, two inputs, thin-edged box. An overview of surviving early AC50s can be found on this page.
19th September
AC50 serial number 1004: two of the original Mullard yellow-print ECC83s fitted by Triumph before the chassis was sent to Dartford Road survive, manufacturing date codes "B3H4" and "B3I3", respectively 4th week of August and 3rd week of September 1963. The paint date codes (the final stage in the production process) are "KK" = November 1963.
18th September
A note on white warning plaques. The earliest AC50s with known serial numbers - 1004 and 1005 - were fitted with a type of plaque (Type 1) visibly different from the type of plaque that came shortly afterwards and remained standard into 1965 (Type 2). The earliest Type 2 plaque known at present occurs on AC50 serial number 1034.
An overview of surviving early AC50s - single channel, two inputs, thin-edged cabinet - can be found on this page. The very earliest AC50s with known serial numbers were different from slightly later ones in other ways too.
The amps issued to The Beatles and The Dave Clark Five evidently had no warning plaques of any sort.
Serial number 1004. Plaque of the same type as on AC50 serial number 1005.
AC50 serial number 1034.
9th September
A series of updates are currently underway, entries recently added for serial numbers 1610, 1628, 1889, 1904, and 2314. Number 2314 was evidently part of a batch (of reasonable size) exported to Scandinavia in 1965. Numbers 2307 and 2338 were also part of this batch.
10th August
Thanks to David, pictures of AC50 serial number 2038, valve rectified (Mark 2), have been added on this page.
AC50 serial number 2038, late 1964 / early 1965.
18th June
Thanks to Richard, pictures of AC50 serial number 2397, probably early 1965, used for many years with a pair of Line Source 40 column speakers.
AC50 serial number 2397.
8th June
Pictures of AC50 Super Twin serial number 7035 - some great details of amp and speaker cabinet - have now been set up here.
6th June
A set of pictures of AC50 Super Twin serial number 7035, one of the two amps illustrated in the previous entry, has now been set up here.
4th June
Thanks to Mark, a superb pair of AC50 Super Twins, serial numbers 7035 and 7139, likely to have bee ready for sale in early 1967. Further details to come.
22nd May
Thanks to Simon, some new pictures of AC50 serial number 1004B. Further shots can be found on this page.
AC50 serial number 1004B.
11th May
Thanks to Dave, pictures of AC50 serial number 3128, along with a cab from a separate source, have been added here. It is probable that the amp was used by the MC5 at one time.
AC50 serial number 3128.
11th April
Thanks to John, further pictures of AC50 serial number 2086, correct sockets now fitted on the back panel, and the amplifier paired with a large-box speaker cabinet (carefully restored). The existing pictures of the amp, one of a small number issued relatively late on in a small box, can be found here.
AC50 serial number 2086.
10th March
Thanks to Dimitrios, pictures of AC50 serial number 6244 have been added on this page.
AC50 serial number 6244.
19th February
Thanks to Glen, some shots of AC50 serial number 2612 - one of two amps with that number, this one with a hand-stamped serial number plate and presumably sent out from Dartford Road, the other with a machine-stamped plate and presumably sent out from the Vox Works at Erith. The amp pictured below is solid state rectified, the other 2612 is valve rectified.
In the first part of 1965, standard practice effectively went out of the window where AC50s and AC30 Super Twins were concerned. Amps were sent out from two locations, chassis evidently sat for longer on shelves, and machine-stamped serial number plates were clearly, at times, affixed on boxes well before any chassis had been allocated to them.
Normal practice at Dartford Road - certainly into 1964 - was to assign and stamp a serial number only after the amp had been made ready for sale and tested.
Solid state rectified. The latest visible date codes in the chassis are one of the pots with "AM" = January 1965, and a Mullard capacitor with "B5" = second quarter of 1965.
Hand-stamped serial number 2612.
Machine-stamped serial number 02612.
The replication of numbers has always seemed a distinct possibility. This however is the first concrete instance that has come to light. Others may of course follow.
18th February
Thanks to Ioannis, pictures of AC50 serial number 5521 have been added here. The latest component date code visible is from February 1966 (one of the pots). The earliest (also a pot) is from November 1964. Certain types/value of components could last a good while.
AC50 serial number 5521.
27th January
Entries for six AC50s with numbers in the 6000s added to this page: 6027, 6330, 6662, 6745, 6822, and 6908.
A new page coming on instances of large box AC50s as Public Address amplifiers. Below, an amp with a serial number in the high 3000s with a set of four Line Source 40 public address speaker cabinets - sold on Reverb a little while ago. The second escutcheon panel on the back panel may have been fitted at factory:
26th January
Entries for a further ten AC50s with serial numbers in the 5000s added to this page: 5172, 5206, 5216, 5228, 5278, 5439, 5754, 5834, 5929, and 5941.
25th January
Entries for four more AC50s with serial numbers in the 4000s added to this page: 4072, 4587, 4654, and 4795.
24th January
Entries for four more AC50s with serial numbers in the 3000s added to this page: 3196, 3611, 3666, and 3975.
23rd January
A couple more AC50s with serial numbers in the 2000s now added: 2187 and 2858.
AC50 serial number 2187.
AC50 serial number 2858, paired with a Thomas Organ Buckingham speaker cabinet.
22nd January (2)
A note on the transformers used by Triumph Electronics for AC50s assembled from late 1963 to the end of 1964 - in other words for the AC50 Mark 1 (single channel amps with two, then four inputs) and for runs of the AC50 Mark 2 (two channel). So far as one can tell, the transformers all had printed paper labels pasted or sellotaped on. Mains transformers were designated "JMI M007A", output "JMI D008A", and choke "JMI X009A". Below, the label on the choke of AC50 serial number 1034. The labels on many mains and output transformers have since come away.
Serial number 1034, detail of choke.
It is not fully certain at present who added these labels: possibly the manufacturer, possibly Triumph, though the former seems most likely. If Triumph did add them - simply perhaps to keep things clearly identified in its stores - then one has to ask why the same sort of labelling was not added to the transformers of other models of amplifier assembled by the company for JMI.
Also to note that the mains and output transformers had part numbers stamped in black ink on their undersides. The output transformer of AC50 serial number 1015 (a Mark 1) has "714216", and the output transformers of AC50 serial numbers 1578, 1610, and 1723 (all Marks 2s) have "105736".
Serial number 1015, underside of output transformer.
Vestiges of a number can occasionally be spotted on the undersides of mains transformers, but heat for the most part has faded the ink to the point of illegibility. The six digit code makes one think in the first instance of Drake Transformers, used by Triumph for the range of PA amplifiers it had been contracted to assemble by JMI. Alan Griffin remembers the sheet metal delivery lorry turning up (male employees were asked to break off from what they were doing to help unload), though unfortunately not the arrival of the transformers.
22nd January
Thanks to Ioannis, a shot of the chassis of AC50 serial number 5521, probably early 1966. The page on amps with numbers in the 5000s can be found here.
AC50 serial number 5521.