Serial number 11954 Treble.

Continued from the page on AC30s with serial numbers in the 10000s. Also encompassed below, some of the last Super Twins that were given numbers in the main AC30 sequence.

One of the features of production in early 1964 - in the 10000s as in the 11000s - is the growing number of "Treble" models. More on these in the section further down this page.

Documents relating to the AC30 in 1964 are being assembled on this page.

Just to recap: from the autumn 1962, JMI had two principal chassis makers working under contract: Burndept Electronics in Erith, and Westrex in Dollis Hill (north London). A sure sign of production by Burndept is the presence of a stamped serial number on the aluminium upright of the preamp chassis (normally on the right hand side a little way below the voltage selector):

Detail of serial number 9916. Chassis number 02607. The sequence began at 1000, but chassis awaiting assembly were not used in any particular order.

Also indicative of production by Burndept at this stage is the presence of Woden transformers with handsome green shrouds. Serial numbers in the 11000s (much as those in the 10000s) have date codes for late 1963 - "JU", "KU" and "MU" = September, October and December 1963; and early 1964 - "AV" and "BV", respectively January and February. JMI evidently ordered sizeable batches. Further details on Wodens are being gathered here.

Serial number 11954 - date code is "AV" = January 1964.

The Woden part numbers were, in order: mains transformer 72318; output transformer no. 66310; and the choke no. 66311. Further details on AC30 transformers in general can be found on this page.

A good indication that a chassis was assembled by Westrex is the presence of Albion tranformers. Dark brown 1/2 watt Dubilier resistors are found along with white Eries.

From early 1964, most Twins have Burndept-made chassis; those produced by Westrex were generally alloted to Super Twins.

Cabinets are in the main covered in black basketweave vinyl, though "pebble" ("dimpled") vinyl was evidently used from time to time, and likewise smooth black or charcoal vinyl. Back boards as a rule now have radiused corners rather than square.

Speakers in "standard" AC30s continue to be the Celestion blue (alnico magnet, Celestion part no. T530) - date codes in early to mid 1964, the final "J" in the code indicating '64. The preceding letter is always the month (A-H, J-M). An overview of AC30s with dated speakers can be found on this page

Serial number 11247, blue with date code "04BJ" = 4th February, 1964.

Treble chassis

A page on the "Treble" circuit can be found here. The key capacitors to check in the first instance are C6 and C9 at the right hand side of the lower tagboard. Those used for Trebles - 0.047uf, or 47000pf - are considerably smaller in value (and physical size) than those used in AC30s with "Normal", "Bass", or "Top Boost" voicing.

It pays to keep an eye out though. At least one amp on this page with a "T" on its serial number plate (to denote "Treble" voicing) is actually a "Normal" model. The only way to determine voicing for certain is to check the value of components at key points in the circuit.

Burndept-made "Treble" chassis normally have TREBLE stamped in red, and a flash of red paint at the right-hand edge of the chassis:

At the volume controls, a network of resistors and capacitors not found in other models:

Detail from a Burndept "Treble" chassis.

Burndept appears to have been maker in chief of "Trebles". There are precious few Burndept-made "Normal", "Bass", and "Top Boost" chassis from this period.

And Westrex was brought in too. Although most of its chassis were reserved for AC30 Super Twins ("Normal", "Bass", and "Top Boost" too), it is clear that a certain number of "Westrex Trebles" were used for AC30 Twins in the low 11000s.

"Westrex Treble" stamped in purply-blue under the input jacks.

The official circuit diagram for the AC30 Treble as we have it (OS/056), is likely to have been created in the first instance for the Thomas Organ Service Center in Evanston following the "Million Dollar Deal" announced in late August 1964. It is dated 10th September 1964. Whether anything existed before that - for the benefit of servicemen in the UK - is unknown at present.

Serial number plates

Serial number plates are still hand stamped. In the low 11000s (but no further than 11166), a type with "AMPLIFIER" rather than "VOX AMPLIFIER" was introduced, no doubt as a temporary measure (as also on AC30s with numbers in the 7400s). These were evidently used through to the 11100s. By serial number 11167 a new plastic plate had been adopted however, carrying through to the 11500s. Although text and numbers have often faded away, raking light normally reveals the impressions. Plastic was clearly a stop-gap though much as its immediate predecessor - the "AMPLIFIER" plate - had been. At some point in the high 11500s standard aluminium plates were reinstated.

Serial numbers 11066 and 11077.

Just to note again, "N" indicates "Normal" voicing (schematic OA/026 and OS/065), "B" is bass voicing. No early schematic survives for the bass circuit, though in relevant respects most amps (from 1962 on) follow OS/065, drawn in September 1964. "T" denotes Treble voicing - schematic also drawn in September 1964: OS/056.

Where component date codes are concerned, speakers consistently have the latest - i.e. later than any of those on the electronic components used in chassis. An overview of AC30s with dated speakers can be found on this page.

The page on AC30s with serial numbers in the 9000s, is here, and the page on serial numbers in the 10000s here.

If anyone knows of further AC30s that should be incorporated on this page, do let me know.

Serial number 11066 T - currently in the UK

Sold in early December 2021 by Gardiner Houlgate, auctioneers. Chassis assembled by Burndept; Woden transformers and choke with date code "AV" = January 1964. WIMA capacitors in the preamp. The serial number plate (as serial number 11076 below) has at its head "AMPLIFIER" rather than "VOX AMPLIFIER".

Serial number 11076 N - currently in the UK

A Super Twin amplifier section. Chassis assembled by Westrex; Albion transformers. Although the voicing is given as "Normal" on the plate, the voicing is actually "Treble" (as in the case of early Burndept-made "Trebles" with serial numbers in the 10000s). The TCC filter capacitor in the preamp has the date code "UG" = August 1963. The serial number plate has at its head "AMPLIFIER" rather than "VOX AMPLIFIER". The number itself overlies a first effort at stamping. Grille cloth is now Rose Morris (from the 1970s).

Updated

Serial number 11077 N - currently in the UK

As serial number 11078 above, chassis assembled for JMI by Westrex; Albion transformers. "AMPLIFIER" instead of "VOX AMPLIFIER" on the serial number plate. Much as in the case of serial number 11077, above, in spite of the plate, the voicing of the chassis is "Treble". In the preamp, WIMA red print signal caps; brown Dubilier resistors. TCC capacitors have date codes "UG", "UJ" and "UK" (250uf, power section) = August, September and October 1963. "DP", the inspector/checker at Westrex, signed off the underchassis in pencil. It is possible that this amp was in the hands of its first owner in late December 1963. Thanks to Glyn for the pictures.

Serial number in the low 11000s - currently in the UK

Chassis assembled by Westrex and stamped "Westrex Treble". The latest component date code known at present is on the tone pot - "AL" = January 1964 for its manufacture. A set of pictures and notes on various aspects of the amp can be found on this page.

Serial number in the low 11000s - currently in the UK

Another "Westrex Treble", in this case just the chassis, so perhaps from a Super Twin. Albion transformers; 50R cathode resistor. The tone pot has the date code "BL" = February 1964 for its manufacture. Evidently a good deal of new work in the preamp.

Serial number 11137 T - currently in the UK

Cabinet recovered in beige. The plastic serial number plate (described in the seller's blurb) has blackened as in the case of the amp below. The general build of the amp looks typical of Westrex - probably a "Westrex Treble", the serial plate now reflecting the voicing (in contrast to serial numbers 11076 and 11077 above).

Serial number 11167 B - currently in the UK

Plastic serial number plate blackened as in the case of 11556 below.

Serial number 11247 B - currently in the UK

Chassis assembled by Burndept, number 038xx. Woden OT transformer with the date code "AV" = January 1964, choke "BV" = February 1964. The date code of the Woden mains transformer is "HW" = August 1965, so not original to the amp, possibly a factory replacement or added by a later repairman. The Celestion blues have date codes "03BJ" and "04BJ" = 3rd and 4th February 1964. The cabinet is covered with thick textured vinyl (dimpled / pebble pattern).

Serial number 11308 B - currently in the UK

Chassis assembled by Burndept. Chassis number 3889. Excellent cosmetic and electronic condition. The Woden transformers have the date code "AV" = January 1964 and the choke "BV" = February 1964. No other component dates are visible though. Signal capacitors are gold-coloured WIMA Tropyfoil (Tropyfol).

Serial number 11350 - currently in the USA

Existence recorded by Jim Elyea.

Serial number 11395B - currently in the UK

Recently sold in the UK. Chassis assembled by Burndept; bass voicing. The Woden mains transformer has the date code "AV" = January 1964. Output transformer and choke are unmarked. In the preamp, a mixture of WIMA and Mullard mustard capacitors, the latter with date codes "A4N and "B4N" (?) = first and second quarters of 1964.

Serial number 11421 N - currently in the UK

A Super Twin amplifier section, numbered in the standard Twin sequence. Note the discoloured plate, typical at this point of production.

Serial number 11444 T - currently in the UK

Chassis assembled by Burndept. The Woden output transformer has the date code "AV" = January 1964. On the back panel an added (non factory) Top Boost unit with an extra "Cut" control.

NEW

Serial number 11450 T - currently in South Africa

Chassis assembled by Burndept, number 04100. Woden mains and output transformers with date code "AV" = January 1964 for their manufacture. The choke is (now) a Radiospares. One of the Hunts cathode bypass caps in the preamp appears to have "YTT" = 4th week of 1964. The yellow-print Mullard ECC82 has the paint code "LA" = Jan. '64.

Serial number 11452 T - currently in the UK

Pictures to follow

Serial number 11542 T - currently in the UK

Probably a "Westrex Treble", though the pictures are a little small, and the preamp is not shown in full.

Serial number 11556 T - currently in the UK

Red paint over the original black covering. Chassis produced by Burndept. The "T" on the serial number plate denotes "Treble", but the circuit is actually "Normal". One of the Celestion blues has the date code "30MH" which is 30th December 1963.

Serial number 11564 T - currently in the UK

Chassis assembled by Burndept, number 03399. A Treble model. Woden transformers with date code "MU" = December 1963. In the preamp, WIMA Tropyfol capacitors. The original brown cover (well worn) survives. Thanks to Brendon for the pictures.

Serial number 11571 T - currently in Europe

Note the blackened plate, much as serial number 11556, above.

Serial number 11613 T - currently in the UK

Complete with its original green cover. Chassis assembled by Burndept. Chassis number 03083. The Woden transformers have the date code "AV" = January 1964. The choke has "BV" = February 1964. In the preamp, the Hunts 25uf cathode bypass capacitors have "IDI" = 38th week of 1963; and the filter cap underchassis "TSI" = 45th week of '63. Note that the cathode resistor is 47ohms.

Serial number 11657 TB - currently in the UK

Chassis number 04616, assembled by Burndept, integral Top Boost controls. The panel is probably from a later amp, however. Note the letters of "JMI" are on separate panels - this comes in in the 18000s (in terms of serial numbers). Note the splash of green paint on the chassis at right to indicate "Top Boost". In the preamp a mixture of WIMA and Mullard capacitors. The latter have the date code "14N" = first quarter of 1964. The cabinet is probably from a later 70s AC30 - three large plastic vents on top and double pins for the corner protectors.

Serial number 11715 T - currently in the UK

Chassis assembled by Burndept; number 03565. Inspection tag still present in the preamp. Thick dark grey textured vinyl on the cabinet (produced for JMI by Gla-Rev); brown grille cloth. The Woden transformers have date codes "AV" = January 1964. Thanks to Andy for the pictures.

Serial number 11718 T - currently in the UK

The cabinet still has its "Super Twin" runner. The chassis - assembled by Burndept and unusual in a Super Twin - is also unusual in having a Woden output transformer and choke (with date codes respectively "JU" and "KU" = September and October 1963), along with an Albion mains transformer.

Serial number 11727 T - currently in the UK

Old pictures. Chassis assembled by Burndept. The Woden mains and output transformers have the date code "AV" = January 1964.

Serial number 11739 N - currently in the USA

In great condition, a Super Twin, chassis assembled by Westrex. Transformers look to be Albion. The original Celestion blues are in place in the speaker cabinet.

Serial number 11769 T - currently in Europe

Chassis assembled by Burndept; number 3094. The Woden transformers have date codes "JU" and "MU" = September and December 1963. The choke has "HU" = August 1963.

Serial number 11781 T - currently in the UK

Grey panel; silver Celestion speakers. Some later work visible on the cabinet.

Serial number 11800 - currently in the USA

A Super Twin amplifier section, a speaker jack socket added on the serial number plate.

Serial number 11873 T - currently in the UK

Chassis produced for JMI by Burndept. In superb original condition - one handle replaced, along with four resistors, two capacitors, but that's it. The circuit conforms to the "Treble" circuit diagram. The Woden mains transformer and choke have the date code "AV" = January 1964. The output transformer has "MU" = December '63. What is probably the original Mullard GZ34 valve survives with the date code "B4A3" - 3rd week of January 1964. Valves did sit in stock for a while (both at Mullard and Dartford Road) before being fitted though. The original Brimar preamp valves also survive. Thanks to John for the pictures and info.

Serial number 11874 T - currently in the USA

Chassis assembled by Burndept; number 3104. The Woden mains and output transformers have the date code "MU" = December 1963. The choke has "JU" = September '63.

Serial number 11912 N - currently in the UK

Sold on ebay in the USA some time ago. The serial number was said to be 11912N, but the chassis stamped "Westrex Treble". Top boost added later "a replica".

Serial number 11954 T - currently in the UK

Formerly owned by Max Boyce. Thanks to Phil for the pictures.

Serial number 11973 T - currently in the UK

Sold on ebay.uk some time ago.

Serial number 11974 T - currently in the USA

Serial number 11982 T - currently in the UK

Serial number 11997 T - currently in the USA

Serial numbers unknown

The chassis below are for the most part Treble models assembled by Burndept for JMI - there is at present one Bass model. Treble voicing is indicated by a flash of red paint, normally accompanied by the legend "TREBLE" stamped in red. On the Burndept chassis colour codes - see this page. A page on Burndept's Treble chassis can be found here.

Serial number unknown - currently in Australia

Chassis number 3018 - TREBLE

Treble model. Chassis assembled by Burndept; number 3018. Woden transformers with date codes "KU" and "MU" = October and December 1963. Hunts capacitors have codes "TWI" and "TDI" = 40th and 48th week of December.

Serial number unknown - currently in the UK

Chassis number 3053 - TREBLE

Chassis number 3053, Treble voicing, assembled by Burndept. The Woden transformers have the date codes "KU" and "MU" = October and December 1963; the main TCC filter capacitor "TDI = 48th week of 1963. The The inspection tag is still present in the preamp. The box has been refurbished with new cloth, handles and corner protectors.

Serial number unknown - currently in Sweden

Chassis number 3086 - TREBLE

The red flash indicates Treble voicing, but the "TREBLE" legend was either not stamped or has since been rubbed away.

Serial number unknown - currently in the UK

Chassis number 3098 - TREBLE

A Treble model. Chassis assembled by Burndept; number 3098. The lower preamp board has been denuded of its components (Vib/Trem circuitry removed). Two of the blue Hunts 25uf bypass caps have the date code "TWI" = 40th week of 1963. The main filter cap has "TDI" - 48th week of '63.

Serial number unknown - currently in Sweden

Chassis number 3265 - BASS

Chassis assembled by Burndept. Chassis number 3265, a Bass model to judge by the blue splash of paint at right. The amp was exported to Sweden early on - voltage selector blanked off and further internal fuses added to bring the electronics into line with local electrical legislation. Note the (unusual) textured aluminium of the preamp upright. One of the pots has the date code "KK" = October 1963. The main TCC preamp filter cap has "IDI" = 38th week of '63; one of the blue Hunts cathode bypass caps has "TNI" = 47th week of '63.

Serial number unknown - currently in the USA

Chassis number 3443 - TREBLE

Woden transformers with date code "AV" = January 1964. The chassis is now in a Super Twin box which may not have been its original home.

Serial number unknown - currently in Europe

Chassis 3465 - TREBLE

A Treble chassis in a home-made cabinet. Chassis number 03465, Treble model. Woden choke and output transformer have the date code "AV" = January 1964. The mains transformer has "MU" = December 1963. Gold-coloured WIMA Tropyfoil (Tropyfol) signal capacitors throughout.

Serial number unknown - currently in the UK

Chassis 3545 - TREBLE

The red flash of paint indicates a Treble model. The Woden output transformer has the date code "AV" = January. The main Hunts preamp filter cap has "TDI" = 48th week of 1963.

Serial number unknown - currently in the UK

Chassis 3571 - TREBLE

Chassis number 3571, the serial number too scratched to decipher. But note the short form of the plate's two panels, as serial number 11954 above. The box is covered in black dimpled vinyl, the voicing of the preamp stamped in red as "Treble" on the right-hand side of the chassis. Both Woden transformers and the choke have the date code "AV" = January 1964.

On to serial numbers in the 12000s.

Back to serial numbers in the 10000s.