The Vox AC10 '2 input vibrato' or "Throwback"
Late 1960 to early 1962
Glen Lambert
Vox AC10 "2 input vibrato" or "Throwback"
An interesting postscript to the TV front G1/10, discussed on this page, is that a number of AC10 '2 input vibrato' amps otherwise known as the 'Throwback' were sold from late 1960 until late 1961, approximately a year after the G1/10 had been retired. These were the same de-featured single channel budget model, priced 10 guineas below the standard AC10 (Amp No.3), and restyled into a new form of split front cab. There appears to have been the additional purpose of using up leftover oddments at Jennings. The obsolete parts used included later riveted G1/10 box type chassis, odd vertically-mounted mains transformers with no 6.3V heater tap (requiring a small auto transformer to adapt a 6.3V tap), G1/10 black fascia plates (with centred 'INPUT' legend), early Univox output transformers, and 1930s vintage 5Y3 large bottle rectifiers. In this instance the term "vibrato" on the pricelist means tremolo. All surviving examples are 'vibrato' having the pre-amp valve deleted from the main lower chassis and a purpose-made 2 x EF86 driven preamp tremolo upper assembly - in the JMI pricelists of November 1960 to late 1961, the "VOX 10W - 2 input vibrato".
November 1960. The last known occurence of the Vox 10W 2-input model is late October 1961. By January 1962 it is gone.
A G1/10 fascia panel used on the AC10 "2 input vibrato" model: Rendar and Re-An input jacks, ivory coloured Radio Spares GS11 knobs (also used by various makers including Roberts Radio and Selmer amps), hexagonal power jewel, Arrow bat-style SPST switch, and B9A three-way voltage selector - which employed a standard 9 pin B9A valve socket with a special rotating plug in top which linked the appropriate pins depending on the position it was inserted. All of these parts were found in other Jennings amplifiers of the era.
Late 1962 AC4 and c. late 1960 AC10 "2 input vibrato" fawn rexine cabinets, showing identical outer dimensions but differing gold perimeter inlay 'string' piping and front valance proportions.
Below, some detailed shots of the power section of the AC10 "2 input vibrato" amp illustrated above:
The AC10 "2 input vibrato" riveted corner "box" style chassis (non-original output transformer). Virtually identical to that in the later 1959 TV front G1/10 amps. Note the unused pre-amp valve opening due to the tremolo pre-amp assembly located at the top of the cab under the control panel.
Very unusual old-style vertical mount 213-228-250 mains transformer with no 6.3V tap. One would take it to be a non original replacment part were it not for the fact that the same transformer with identical hookup wiring has been documented in at least two other "10W 2 input vibrato" amps of the period.
Filament auto-transformer located inside lower chassis to produce the required 6.3Vac, due to the odd mains transformer.
The original small output transformer of another Throwback, the horizontal frame similar to that used in the Univox keyboard amp and the G1/10. The small tagstrip attached to the top has a couple of free terminals that were not internally connected and could be used for joining wires or even mounting a component, as was done with the choke.
The rear grey painted masonite cover of the AC10 '2 Input Vibrato' Throwback amp. Single Speed control mounted through rear cover and opening for cable and pedal storage. A proper serial number plate was used on these, one of the surviving amps for example being numbered 3431 (indicating 1960), another 3640 (suggesting 1962).
The AC10 "2 input vibrato" amp may have been the first "fawn" amplifier into production: the cabs presenting a series of new features which became standard on all subsequent amps, but retaining the island style control cutout, and single-piece slotted masonite (hardboard) rear cover similar to the earlier TV front cabs. Indeed, the Throwbacks were probably the earliest to have 'split fronts', albeit with design proportions not yet perfected. They had a very small rexine covered 'valance' area at the top of the front baffle with a comparatively large area of grille cloth; gold 'string' inlaid around the perimeter (though at a different spacing to later amps); and brass vents. They may have been a developmental cab or even a first run intended for the AC2 but set aside in favour of the more familiar design proportions used in subsequent amplifier cabinets.
These amps were in the same '3XXX' serial number range as all other varieties of AC10, but several hundred units later than the last known TV front G1/10 amps in the sequence. Dates on components found in surviving examples suggest they were made in mid 1960 but some were stamped and sold as late as 1962. These amps were fundamentally still Derek Underdown's G1/10 design and may have also been a side project of his to have various left-over parts finished off. There was certainly some effort and work undertaken to achieve an attractive and serviceable result. It's also nice to note that Derek had his original G1/10 design still in use in the early 60's. The 'W' stamp on the serial number plates may signify that the assembly of these amplifiers was contracted out to Westrex.
Thanks to Valentin of Finland for measurements and images of his fawn AC10 Throwback amplifier.