Determining Date of Manufacture

Last updated December 14, 2009

Note: The numbers below are for Hylight and Biacrown Hiwatt amplifiers only! Any serial number that begins with one or more letters was made in the 90s or later, and is not included in this list. Please note also that the speaker cabinet serial numbers used a different progression. Please browse the Registry page for more specific data relating serial numbers to dates.

I have not yet managed to collect enough information on the later models carrying the Hiwatt brand and manufactured by Turntone or Sterling, e.g. the Model 50L. The serial numbers of these newer models often fall within the ranges listed below, but these were manufactured in the mid-80s and later. Turntone started the "L" series of amps in 1985 or so, and these have no manufacturers brand on the serial plate, but say "Made in England."

Amps made by Sterling Imports were made in California, USA, and have that brand name on their serial plate.

Amplifiers with a serial starting with "AB" were made by Audio Brothers in England the 1990s.

Amplifiers with a serial starting with a single letter and bearing a plate which has "HIWATT UK" and LONDON or DONCASTER on it were made starting in the early 2000s by the current Hiwatt manufacturers, Music Ground.

All units manufactured by Hylight Electronics from 1966 to 1981 had a serial number plate like the ones in the pictures below attached to the metal chassis of the amplifier. All of these plates bear the marking
to identify the manufacturer. Note that sometimes speaker cabinet plates were "cut down" and used when the stock of normal plates ran out!

Early Plate Later Plate
Cut-down Plate

All units manufactured by Hiwatt Biacrown from late 1981 to 1984 had a serial number plate like the one in the picture below attached to the metal chassis of the amplifier. All of these plates bear the marking
to identify the manufacturer.

Surbiton Factory

Many of the units made from 1971 to 1984 that were wired by the crew at Harry Joyce Electronics were often times so marked on the chassis with a blue, black or red marking pen:
Several units also had a small white tag affixed to the inside of the chassis which bore initials (or "T/S" for "Tested and Soaked") and a wiring date. NOTE: Harry's name on the chassis has some perceived value, and forged "Harry Joyce" signatures have been seen in the wild.

Note that other firms (as well as the crew in-house) did some wiring for Hiwatt at various times throught the company history, because Joyce would only produce a limited amount of chassis each month (20...40; accounts vary).

An important item to remember is that the date that the wiring crew put on the amplifiers was the date that they completed wiring the chassis for Hiwatt, not the date of final manufacture of that unit.

As with dating any other piece of vintage musical equipment, there are discrepencies. The numbers listed below are within a year or so of when the actual date of manufacture occurred. The Hylight/Biacrown transistion numbers are particularly vague, as Biacrown likely used up the existing supply of Hylight plates before ordering their own.

These dates will be revised from time to time as data from the Hiwatt Registry page and other sources accumulates.

(Last revised 11/2009)

Serial # Range Approx. Year Of Mfr. Place Of Manufacture
010 - 299 1966-7Morden
300 - 449 1968Morden or New Malden
450 - 709 1969New Malden
710 - 1499 1970New Malden
1500 - 2499 1971New Malden
2500 - 3999 1972New Malden or Kingston
4000 - 4999 1973Kingston
5000 - 7999 1974Kingston
8000 - 8999 1975Kingston
9000 - 9999 1976Kingston
10000 - 118991977Kingston
11900 - 129991978Kingston
13000 - 142991979Kingston
14300 - 149991980Kingston
15000 - 154991981Kingston or Surbiton (Biacrown)
15500 - 159991982Surbiton (Biacrown)
16000 - 169991983-1984Surbiton (Biacrown)

Units bearing the Sterling serial plate were manufactured by Sterling Imports at their Modesto, California facility in either late 1984 or 1985 (these serial numbers were not consistent).

* Much of the original research was done by Dave Wild of Wild Guitars, UK. Other information has been obtained by personal accounts from individuals and via the Hiwatt registry. Thanks to all have contributed!

Note that manufacturer date codes stamped onto the original internal parts can be used to positively establish a "not manufactured before" date. The parts were likely manufactured one to twelve months (sometimes longer) before being used to build an amp or fill a speaker cabinet.

These date codes are of the form "YY WW" or "WW YY" where YY is the year and WW is the week of the year (the week is the one <= 52) . Here are some examples (images courtesy of Clayton C.):

Cap can: 20th week of 1969
Cap can: 48th week of 1969
Cap can: 14th week of 1971

Pot: 47th week of 1968
Pot: 37th week of 1973

Speakers: date code location
Speaker: 51st week of 1971
Speaker: 31st week of 1971
Speaker: 13th week of 1977

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