Vox AC30/6: black panels, split-front cabinets
mid/late 1960 - late 1961
Cliff Richard and The Shadows, and the new split-front AC30 in the booklet of early 1961.
As noted on the previous page, for around fifteen or so months production of the AC30/6 went side by side with that of the AC30/4. To simplify assembly, all preamp chassis were drilled for six inputs, the two that were superfluous for the AC30/4 being blanked off when the control panel was fitted:
A detail of the chassis of serial number 4715.
"Melody Maker" magazine, 30th July, 1960. The earliest dated advert for the AC30/6 to have emerged so far. Paul was Paul Jennings, son of Tom, and manager of "Musicland" at 88 Broadway, Bexleyheath.
Also in "Melody Maker", 30 July, 1960, was an advert featuring Shirley Douglas and Chas McDevitt and mentioning "*new Vox amplifiers". Much the same ad featuring Chas and Shirley had appeared a fortnight earlier, but without the mention of anything being new. See this page.
The first formal note of prices in the music press came in November 1961:
"Melody Maker" magazine, 19th November, 1960. The AC30/6 is 89 guineas; the AC30/4 is 85 gns. There is also an AC30/4 Bass model at 89 gns.
The serial numbers of black panel AC30/4s and AC30/6s ran from the outset in the same sequence - from the low 4200s to low 4700s. When the AC30/4 was phased out in October 1961, the AC30/6 Twin shared the continuation of the sequence with the new Super Twin through to 1964, black panels giving way to copper in late 1961 - see this page.
As there was no such thing as a black panel AC30/6 Bass, one only finds the designation "N" = Normal voicing. The AC30/6 Bass came a little later. The "W" (an upside-down "M") - also found on the plates of AC30/4s - may signify something along the lines of "wide frequency", distinguishing these amps from the more constrained tonal response of the early AC2/30 and AC/30.
Vox AC30/6 serial number 4680.
The speakers chosen for the split-front cabinet were new - and standardised (or at least regularised): the Celestion "blue" - G12 alnico T530, sprayed Jennings blue - as depicted in the page from the brochure below.
Note that the brochure illustrates a control panel for the new circuit of the AC30/6.
Although the AC30/6 became, in late autumn 1961, the principal model offered by Jennings, orders for the AC30/4 were still honoured at the old price of 95 guineas (£99 5s). See the documents on this page. For a limited time, however, the AC30/6 could be had at the special price of 100 guineas (£105) - a canny means of helping along the phasing out of the AC30/4 and the move to the new amplifier.
CIRCUIT AND COMPONENTS
The key differences between the AC30/6 and AC30/4 lie principally in the preamp. There is a single treble "cut" control instead of the dedicated bass and treble controls of the AC30/4. The EF86 is replaced by an ECC83 - one half each for the first stage of the Brilliant and Normal channels. And of course, there is the Brilliant channel itself, whereas before there had only been the Normal.
A more detailed description of the circuit will be reserved for another page. For the moment, simply to say that the changes introduced in May 1961 served to lift the gain of the amplifier (Brilliant channel in particular) and to enhance irs treble response.
The schematic for the AC30/6 is JMI sheet [O]A/026 (drawn 29th April 1960). Changes to the circuit are noted on the upper right hand side of the sheet. A/026 was later renumbered as OS/065.
Detail from sheet A/026. Drawn on 29th April 1960. Annotations are the same as on OS/065.
The transformers for both the AC30/4 and AC30/6 were made by Haddon ("Haddon Transformers Ltd." of South Ruislip), the choke by Radiospares. Resistors are white 1/4 watt Eries; coupling capacitors by and large are black WIMA Tropydurs; and filter capacitors are Hunts, Radiospares, and TCC. Potentiometers were made by Egen Electric Limited. The valves originally fitted are likely to have been yellow-print Mullards.
Up to Spring 1961, chassis were assembled at the Vox works at 115 Dartford Road. For pictures of the site and the factory, see this page (on the Vox AC100 website). Thereafter, chassis were assembled for JMI by Westrex at its Coles Green Road works. They are instantly recognisable by the presence of red dye on the solder joints, daubed on at point of inspection to indicate that the joints were good.
Notes on how to read component date codes, are available here.
Jim Elyea's book, "Vox Amplifiers. The JMI Years" (California, 2009) is again a wonderful repository of info on these amps and other AC30s.
"A Service Engineer's Guide to the Vox AC30 Valve Amplifier" by Stephen Grosvenor (2006), gives excellent schemas of the circuit boards and electronic layout. His site is here.
If anyone knows of further early new-style black panel AC30s that should be incorporated on this page, do let me know.
AC30/6 - black panel from mid 1960 - late 1961.
The new AC30/6 escutcheon panel, laid out for six inputs, vib/trem settings, three channels, and a single tone control.
Serial number 4350 - currently in the USA
Picture from Jim Elyea's book. Pre-production traffolite control panel with individual bounding lines for the controls. A similar panel, in a slightly more developed form, can be seen on an early AC30/4 chassis (or at least the remains of one) - at the foot of this page. The relevant image is this one:
The controls on this panel have captions and within the compartments there are marked settings.
Serial number 4463N - currently in the UK
The Shadows' amps - issued in March 1961
NME Poll Winner's concert, 5th March 1961. Photographed by Harry Hammond.
Note the logos high up on the front and the special "The Shadows" legend. Picture from Getty Images.
Below, some interesting details from pics taken on 18th June 1961 - The Shadows playing in Calais, a day trip planned as a double bill with Gene Vincent, though Vincent was in the end unable to appear. There's a short newsreel clip of The Shadows' performance on youtube.
The pics show the backs of the band's first set of split-front AC30/6s - smooth black vinyl, brass vents, black leather handles, black and gold circular control knobs, and the serial number plate of at least one amp on the lower back panel (rather than the upper, as is normal).
Note that the amp has five screws along the top edge of the top back board.
Serial number unknown - currently in Australia
Thanks to Guy for the pictures.
Serial number unknown - currently in the UK
Cabinet, speakers and chassis original from factory - the amp evidently much used over the years. Sold twice in the UK (two sets of pictures, the first from some time ago). No component date codes known at present. The main filter capacitor in the preamp (silver can) is a later TCC-Plessey component.
Chassis - currently in Australia
The blue Hunts capacitor has the date code "YAW" = 9th week of 1961. The TCC capacitor next to the choke has the code "SC" = March 1961; the tone pot is also March 1961 = "CI". The grey Radiospares coupling capacitors are replacements for the original black WIMA Tropydur.
Chassis - currently in Australia
Main filter cap., Hunts date code "NWW" = 17th week of 1961. Hunts cap. under chassis date code "YI W" = 3rd week of 1961. Green TCC preamp filter capacitor date code "RA" = January 1960.
Chassis - wherabouts unknown
Pre-list-of-changes AC30/6 chassis slipped into the trapezoidal cabinet of a much later AC30 Super Twin. Mains transformer has been replaced. The original Haddon output transformer and Radiospares choke survives A modern top boost unit has been added.
Serial number unknown - currently in the USA
A later assemblage. Cabinets recovered in Korg white vinyl from one source, chassis from another. Note the separate tagboard at left (with green capacitors) for the vibrato/tremelo footswitch circuit.
Serial number unknown - whereabouts unknown
Now in a post-1964 cabinet (assuming the silver alnicos are original to it). Note the small tagboard at left - therefore likely to be pre-"list-of-changes".
Serial number unknown - currently in the UK (?)
Now in an AC30 Anniversary cabinet, the original serial number plate transfered to the back panel. The small tagboard is visible in the preamp at left. Voltage selector set to 245v. The chassis may be that of the amp immediately above - note the orange capacitors.
Post "List of Changes" - 8th May 1961
"Melody Maker" magazine, 20th May, 1961, the AC30 in view said to be "New" - re-stated in the first line of the text: "new series amplifiers" - corresponding to the "List of Changes" noted on the circuit diagram, 8th May 1961.
Serial number 4680 N - currently in the USA (?)
A Super Twin box with the chassis just visible inside - nothing else for the time being. The serial number plate is genuine (and original), non-standard for AC30s though. Interesting to see the remains of black cloth under the plate.
Below, the serial number plate with a black panel AC30/6 chassis. Not sure what happened to the box. If box, plate and chassis originally went together, then this was a very early Super Twin.
Serial number 4760 - cabinet and serial number plate only
Position here is provisional (the original chassis is gone). Note however that the serial number plate is of the same type as the amp above.
Click for a larger version of this image.
Old pictures from ebay. Sold in May 2007. As the seller stated, the chassis is a replacement for what was there originally. The Woden transformers have the date codes "HU" = August 1963.
Serial number 4696 - currently in the UK (?)
Old pictures from ebay. Sold by Electromusic of Doncaster in June 2007, shadows of stickers on the front. The original footswitch survives. Blowing the thumbnails up well beyond their natural size shows that the amp is an AC30/6 post-list-of-changes.
Serial number 470x B (?) - currently in the USA
Pictures from the early 2000s. It seems probable that the chassis is not original to the box. Note the new slider board and the presence of silver alnico Celestions. If that is case, and if the plate does actually read "470x", which is certainly in the right range for an amp of this type, then the plate must have been transferred from the old box too.
Serial number 4754 - currently in the UK
Cabinet refurbished and in good order. Interesting to see that there is no designation of voicing ("N" or "B") on the serial number plate. One of the pots has the code "FI" = June 1961.
Serial number 4756 B - currently in Europe
Serial number 4763N - currently in the UK
The chassis was formerly in a box with a repro / fake serial number plate - 5014T. There was no such thing as an AC30 "Treble" at this point.
Serial number unknown - formerly in the UK
Sold on ebay some time ago - May 2007. No info at present on whether the amp is Pre or Post "List of Changes", so placed here on a temporary footing. Transformers are Haddons (stickers visible on the shrouds). The choke is very ruddy in colour.
Serial number unknown - currently in Europe
The box, which is early (square corners to the back boards), has been recovered. It is not known whether either of the two speakers is original to it. At this stage in production, JMI is unlikely to have sent out an AC30 with one speaker specially labelled and the other not.
The black control panel is a reproduction (but may replicate what was there originally). The serial number plate on the back panel is also a reproduction.
As in the amp immediately below (currently in Australia) the chassis has a phantom cut-out for the GZ34 valve.
The pictures above show the amp before it was serviced. The transformers are Haddons. One of the pots has the date code "FI" = June 1961. Three date codes on the Hunts capacitors are also visible: "HWW", "HTW" and "HSW" = respectively 21st, 24th and 25th weeks of 1961 (June and July).
Serial number unknown - currently in Australia
The amp is in its original box. The serial number plate (5984N) is from a later copper panel AC30. Thanks to Guy for the pictures.
Serial number unknown - currently in the UK
The speakers accompanying the chassis have date codes 24EG and 25EG = 24th and 25th May 1962. It seems unlikely however that they belonged originally to the cabinet that housed the chassis.
Copper panels appear in the high 4000s, see this page - AC30s in beige cabinets, copper panels.