UPDATES
Older blog / update entries are now here.
2025
10th May
Two early Mark 2 chassis both in small boxes from factory, cathode bias resistors added later. The EL34s in serial number 1311 wee given a 50R resistor each, imitating the arrangement set out in the circuit diagram for the AC50 Mark 3 (OS/072, 47R resistors specified). The other amp, much modified, has 150R resistors with cathode bypass caps, the latter 1970s metallic green 32uf/150v TCC/Plesseys.
In both amps the fixed bias network is still in place and in circuit. The reason for the additions? To spare the valves. Standard bias in these amps (ie. from factory, not modified) was -34v.
Serial number 1311, early Mark 2 chassis.
Serial number unknown, also an early Mark 2 chassis.
25th March
A superb AC50 SDL - serial number 4709 - complete with original cables (with Amphenol connectors). Thanks to Arjan for the pictures.
AC50 serial number 4709.
9th March
AC50 Foundation Bass serial number 1379, an early large box amplifier section with a single Cannon socket mounted on a vinyl-covered block on the back panel.
The speaker cabinet had evidently been got at by wordworm at some point - disclosed perfectly properly by the seller - but looked generally to be solid and in good order otherwise.
Original cables and cover for the amplifier section were all present. Further pics are on this page.
4th March
Thanks to Andrew, pictures of AC50 serial number 3065, mid 1965, have now been added on this page.
AC50 serial number 3065
2nd March
Thanks to Sam, pictures of AC50 serial number 2685 have now been added on this page. The amp is likely to have been part of a batch sent to the USA by JMI in the early Spring of 1965.
AC50 serial number 2685, pictured with a V125 cabinet.
1st March
A couple of cabs with single-letter logos, the first from late 1964 (with Celestion T1088s), the second from early 1965 (with Fanes).
22nd January
Thanks to Christian, the serial number of the first MC50 illustrated on this page has now been corrected - 2666, NOT 2885 as originally stated. An entry for the amp has also been made - here - in the main guitar/bass amplifier sequence.
21st January
Thanks to Dan, pictures of AC50 serial number 5393, early 1966, can now be found on this page.
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.
