Vox AC30 Super Reverb Twins
Later amplifiers in "slope-sided" cabinets.
1965 to 1968 - grey control panels
Serial numbers in the 3000s-5000s
The new format AC30 Super Reverb Twin represented in the "Precision in Sound" newspaper format catalogue of late 1964. Note that the amplifier section has sloping sides. The chrome stands on top of the speaker cabinet were a pre-production try-out. Production amplifiers had standard full trolleys.
A heat in the Thomas Organ Vox "Battle of the Bands" competition held at the San Mateo fairground in April 1965. On stage, a slope-sided Super Reverb Twin.
Earlier "Super Reverb Twins", that is to say from Spring 1962 to late 1964, can be found on this page. Cabinets for amplifier sections were initially exactly the same as those used for plain "Super Twins". "Super Twins" from 1964 are gathered together here.
A design for the Super Twin amplifier section registered by JMI with the Patent Office on the 28th August 1964. The other pictures submitted to the Office will be made available shortly (Nov. 2021) on a new page. Production slope-sided cabinets for AC30 Super Twins took a different form - see below - and did not really come "on stream" until early 1965.
Slope-sided cabinets were first used for "Super Reverb Twins" in early 1965. A few months later they were adopted for standard "Super Twins". The earliest AC30 SRT to have come to light to date with such a cabinet is serial number 3523 (below). The earliest slope-sided AC30 ST is serial number 3863.
This new style of amplifier section cabinet was taken up later by Thomas Organ for its solid state range: the Berkeley, Royal Guardsman, and Super Beatle.
In order to avoid paying a license to use an existing reverb design (from Hammond, Accutronics, and so on), JMI came up with its own. In the first instance, a pair of springs in parallel, with phono cartridges - normally white ACOS units - at the ends to serve as transducers. The tray containing the springs was suspended in the reverb enclosure by rubber bands in order to isolate it as far as possible from external vibration - it worked (to a degree). ACOS cartridges remained in general use through to 1966, after which time red Sonotones came in. Later reverb tanks had only one spring. A schematic for an add-on reverb unit, to augment standard AC30s, was drawn up on 15th January 1965 - OS/075.
Details of a single-spring reverb tray from a later sloping-sided AC30 SRT. Note that the rubber band (first picture, top left) has perished and no longer extends across the width of the tray through the black rubber grommets to suspend (isolate) it within the enclosure. One can just see the details of the ACOS cartridge - Stereo, GP 71.
Controls were on the back panel in a cut-out; reverb tray enclosure and driver transformer mounted on the underside of the amplifier's slider board. Early examples are scarce.
The controls on the back panel of AC30 Super Reverb Twin serial number 5031. Only the "E" of the legend "EFFECT" is visible.
AC30 SRTs destined for export to the USA were often fitted by JMI with a 0.05uf 500v Radiospares capacitor from the mains switch to ground - a means of suppressing arcing, if there should be any, at switch on. The capacitor does not appear on any circuit diagram. AC50s and AC100s were also fitted with these capacitors (again not represented on any of the sheets that have come to light).
AC30 Super Reverb Twin serial number 5031.
A detail from the JMI retail pricelist of November 1965. Four versions of the AC30 SRT were available - the AC30 SRT/I with one speaker cabinet; the AC30 SRT/I with Top Boost; the SRT/II with two 2x12" cabinets; and the AC30 SRT/II with Top Boost. Dealers in larger cities regularly sold AC30s at substantial discount, however.
"Melody Maker", 5th March, 1966 - a detail from an advert placed by Pan Music of Wardour Street. An AC30 SRT and two single 12" cabinets (these normally had fixings for wall-mounting) at £85.
If anyone knows of further Super Reverb Twins that should be incorporated on this page, do let me know.
Serial numbers in the 3000s (continued) - 5000s
Model designation ("AC30 S/T") and serial numbers are machine stamped on the plates of the amps on this page. Designation of voicing and reverb are generally hand stamped however.
Serial number 3523 - currently in Germany
Sold on ebay some time ago. The Woden transformers appear to have the date code "KV" = October 1964.
Serial number 3541 - currently in Germany
The Woden output transformer has the date code "KV" = October 1964, the choke and mains transformer "EW" = May 1965.
Serial number 3549 - currently in the USA
Serial number 3570 - currently in the USA
Purchased second-hand in San Francisco in 1968 and still in working order. Note the unusual designation on the plate - "RTB" = Reverb Top Boost. Thanks to Marc for the info and pic.
Serial number 3711 (?) - currently in the USA
The Woden transformers have the date code "KV" = October 1964, the choke has "BW" = February 1965. In the preamp, the Mullard mustard capacitors have "A4N" and "B4W" = first and second quarters of 1964. By the mains switch is the grey Radiospares capacitor (not on any known circuit diagram) which was added by JMI to amps destined for the USA.
Serial number 3767 - currently in the UK
The plate alone sold on ebay.
NEW
Serial number 3848 - currently in the USA
A detail of the stamp "T B" for Top Boost.
Further details of the preamp are on this page.
The rig was first sold complete to its original owner as a "Buckingham" in late 1965 by a music store in Alabama USA. Sold on in the early 1970s, it then passed to its current (third) owner in 2007. The amp is currently in Eastern Pennsylvania.
Chassis assembled by Burndept - "T B" (for Top Boost) stamped on the preamp upright at left. Chassis number 11101. The flash of green paint at right in the preamp also indicates that Top Boost controls are integrated in the control panel. The Woden output transformer has the date code "JV" = September 1964; choke and mains tranformer are Albions. In the preamp Mullard mustard capacitors with "B/64" and "C4N" date codes = second and third quarters of 1964 for their manufacture. Original covers for both sections are still present. The original god-coloured Oxford speakers were replaced with a Celestion silver, reconed by Celestion in the late 1960s, and a blue, repaired by Orange County Speakers in California in 1994. Thanks to Rich for pictures and info.
Serial number 4313 B - currently in the USA
A superb Super Reverb Twin. Chassis number 12618, produced by Burndept Electronics and still with its inspection tag, signed off by "Newcombe". Visible date codes are "B4W" on the mustard capacitors = second quarter of 1964; and on the gold-coloured TCC 25uf cathode bypass caps "WC" = March 1965 (or perhaps "WE" = May). The speaker cabinet was made ready (given vinyl, grille cloth, fittings) by "Alice". Thanks to Jet for the pictures.
NEW
Serial number 4655 TB - currently in the USA
Chassis probably assembled by Westrex; Albion transformers. In company with serial number 4691 below, a Top Boost Super Reverb Twin. Probably long in the USA. Good external order. Speakers are now later Celestion ceramics. Thanks to Marc for the pictures.
Serial number 4691 TB - currently in the USA
Chassis assembled by Burndept, chassis number 10864. The Woden output transformer has the date code "KV" = October 1964, and the choke "AW" = January 1965. The power transformer is a replacement. In the preamp, the mustard caps have "B4N", "C4N" and "D4N" respectively second, third and fourth quarters of 1964. One of the blue Hunts cathode bypass caps gives "IYT" = 30th week of 1964. The back panel has an amazing number of sockets. Thanks to Stephen for the pictures.
Serial number 4842 - currently in the UK
Thanks to Tim for the pic.
Serial number 4857 - currently in the USA
Sold by Heritage Auctions some time ago. Reverb has been removed and the serial number plate moved to cover the hole formerly occupied by the controls on the back panel. The "Super Reverb Twin" runner remains on the front grille.
Serial number 4858 - currently in Germany
Note that "Reverb" is not designated on the serial number plate.
Serial number unknown (high 4000s / low 5000s) - currently in the USA
Chassis assembled by Burndept - number 10375, the flash of green paint at right indicating that this is a Top Boost model. With the usual caveats, note that serial number 5031 (below) has chassis number 10371. Transformers are Parmekos. In the preamp, a mixture of WIMA and Mullard mustard caps, the latter with "B/64" and "C4N" date codes = respectively second and third quarters of 1964 for their manufacture. One of the TCC cathode bypass caps has "WD" = April 1965. In company with a number of other Super Reverb Twins, this amp was specifically produced for export to the USA - an 0.05uf Radiospares originally wired to ground across the mains switch (to conform with UL requirements). One can see the hole for the bracket in picture no. 6 above. Thanks to Steve for the pictures.
Serial number 4907 - currently in the UK
Thanks to Bill for the note on the amp's existence.
Serial number 5031 - currently in the USA
Chassis number 11371. Mullard mustard capacitors in the preamp have the date codes "B4N" and "C4N" = second and third quarters of 1964. One of the blue Hunts cathode bypass capacitors has "HWT" = 21st week of '64; another has "WWS" = 11th week of 1965. The large TCC 8uf electrolytic has "VF" = June 1964. The mains and output transformers are Albions, the choke a Woden with "BW" = February 1965. The grey capacitor underneath the mains switch was added in England as a "snubber" to suppress surges at switch on in amps sent to the USA. Capacitors of this type were also added to AC50s and AC100s allocated for export. They were not marked on the circuit diagrams.
Serial number 5116 - currently in the USA
Chassis assembled by Westrex. The Reverb unit has been removed and the serial number plate repositioned to cover the opening in the back panel. Cabinet recovered and re-grilled. In the preamp, WIMA capacitors. One of the pots has the date code "JL" = October 1964, and one of the TCC electrolytic capacitors "VF" = June '64. The amp was probably ready for sale at some point in the first half of 1965. Thanks to Cameron for the pictures.
Serial number 5132 T - currently in Australia
Thanks to Greg for the info.
Serial number 5195 T - currently in the USA
Currently (December 2020) here.
Serial number 5207 - currently in the USA
A Super Reverb Twin amplifier section in old-style rectangular cabinet.
Serial number 5223 T - currently in Germany
Sold on ebay some time ago. The reverb controls have been removed. Transformers are Wodens. A square-sided box, as in the case of certain late Super Twins.
Serial number 5262 TB
A top boost model. Thanks to Johnny for the pictures.
Serial number 5263 TB
Plate only.
Serial number 5301 TB - currently in Europe
Chassis number 12492. The Woden choke has the date code "HW" = August 1965; the mains transformer "EW" = May 1965. The majority of the Mullard mustard capacitors in the preamp have "D4N" = last quarter of 1964. The gold-coloured TCC cathode bypass caps have the date "WE" = May '65.
Serial number 5318 TB - currently in the USA
On the serial number plate: 05318 TB RV. Sold on ebay a while ago. Pictures and text of the auction page can be found here.
Serial numbers unknown
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