Cathode-biased AC80/100s - Spring 1965
Serial nos 320 - 380
GREY PANELS, DOME VOLTAGE SELECTOR, SMALLER CHOKE
In early 1965 Vox transferred production of the AC80/100 from Westrex, one of its principal contractors in 1964, to the new Vox Works on West Street, Erith.
A small run of amps with black control panels was produced initially. Thereafter they were grey, 140 or so being produced from February/March - June/July 1965.
A typical early grey panel chassis. This is serial number 392, slightly later than the amps on this page, but representative of the standardised production at the Vox / Burndept Works in the first half of 1965. Number 392, in company with many of these amps, was made for export to the USA.
New elements were introduced: the smaller choke (rated at 19H 100mA), white Erie resistors, and a chassis number stamped on the left hand side of the aluminium preamp upright (normally just above the terminal block for the output connections) - all marking a break with standard Westrex practice. Gone too is the red dye on the solder joints.
Many of these amps were shipped to the US in 1965, probably in large batches. A good number survive there too.
One can often spot in the "US export" amps an extra capacitor (not on the schematic) up by the mains switch in the preamp - a grey Radiospares (ie. English) 0.01uf, 500V. Its purpose was to suppress arcing across the mains switch. All US-made Gibson and Fender amplifiers had similar caps as a matter of course.
The cap. in question is above the green TCC filter cap. The AC80/100 schematic is on this page.
In spite of the fact that these amps run hot, they have lasted well - illustrated by the examples collected below and on subsequent pages. In the second half of 1965, however, JMI, moving with the times, redesigned the AC100, changing its circuit to fixed bias - the "100W amplifier". For examples of these amps - see this page.
If anyone knows of further grey panel cathode-biased amps, please email me at click here for the address. This page will be updated, so please come back to look from time to time.
Serial number 320 - currently in the US?
Sold on ebay some time ago. Grey panel, dome voltage selector, and Woden transformers with unpainted shrouds. The code on the (small) choke is AW = January 1965, and the codes on the mains and output transformers BW = February 1965 - the same as for serial number 337, below. The amp seems later to have been changed to fixed bias - note the new 220K grid resistors in the last picture. Thanks to Paul Johnson for the images.
Serial number unknown - currently in the US
This amp actually inhabits the box with serial no. 880 - on this page. The chassis number is 1040. The serial number of the original box will have been somewhere in the 300s. Transformers are Wodens with unpainted shrouds, the choke is of the later stand-up type (19H 100mA). There are a few new components in the preamp, but otherwise all intact. Condition is great. Thanks to Dave for the photos.
Pictures pre-restoration (ie. as above)
Pictures post-restoration (2015)
Expertly restored by BLC.
Serial number 323 - currently in the US
A nice early grey panel AC80/100 with a handsome bass rig. Thanks to Christopher for the pictures. Below, the original box.
Box of serial number 323, now in the UK. Made by GlaRev - the stencil just visible on the left hand inside. Single fixing point along the top edge. Arrangement of back panel as in no. 328, below. The Cannon connector was just popped in for the photo.
Serial number 328 - currently in St Louis
Chassis no. 1007. Grey panel; Woden transformers with unpainted shrouds, date code "BW" = Jan. 1965, as most AC80/100s on this page (evidently a job lot bought in by Vox). Carefully restored to full working order by the present owner. The wiring and various components in the power section had suffered from current-induced heat damage, the original bias resistors really only being correct for 110V, not the 120V delivered from wall sockets. Original connectors on the back panel. On the front, a cloth similar to that used by Jennings Electronic Industries. However, inspection showed that there were no signs of its having been replaced (no "old" staple holes in the white piping) - and there is reported to be one other amp in this rare custom cloth. This AC80/100 was acquired from the studio of Oliver Sain, friend of (and occasional musical collaborator with) Ike Turner, a Vox-endorsed artist. It is likely to have been part of a batch imported by the Thomas Organ Company in early to mid 1965 for sale in the US (note also the US provenance of serial numbers 331, 337, 406, 416 and 420 on this page).
Serial number 330 - currently in the US?
No pictures available, but reported as having a black panel by J. Elyea, Vox Amplifiers, p. 446. Click here for a discussion of AC80/100s with black panels on a Plexi Palace thread.
Serial number unknown - though certainly 300s - currently in the US
Chassis number 1011. Grey control panel; Woden transformers. Reported by the amp's owner on a beatgearcavern.com thread.
Serial number 331 - currently in Florida (collection: Kent Pearson)
Chassis number 1030. Cathode biased. A nicely restored AC80/100, in the first picture sitting on top of a reproduction cabinet and trolley made by North Coast Music. The second picture shows the new reproduction copper panel, along with the original white warning plaque, serial plate and speaker XLR. In the other pictures one can see the new-style choke, and the white Erie resistors, which one also finds in AC100 Mk2 amps.
A great shot of the amp, cab and Telecaster.
Serial number 337 - currently in Sweden
Sold in October 2010. Cathode biased. A nice clean AC80/100, probably made close to the end of the "formal" cathode biased production run. In the second quarter of 1965 JMI evidently assembled cathode biased amps side by side with the new fixed bias ones. Note in this instance the small choke, dome voltage selector, Cannon LNE-32 mains socket, and unpainted shrouds on the Woden transformers. This amp was for years pictured on the Vox website (in their archive) with the suggestion of possible use by the Beatles, a claim that unfortunately cannot be substantiated. Capacitor codes WA = January 1965; the Woden choke AW = January 1965; and the Woden mains and output transformers BW = February 1965. The last picture shows the amp in its new home in company with an original T60 cab and reproduction trolley.
Serial number 338 - formerly in the USA
Sold in October 2012 (Heritage Auctions, first set of pics); and on ebay in January 2012. Chassis no. 1039. Good overall cosmetic condition. Converted from cathode bias to fixed bias (and the preamp also adapted to the fixed bias circuit). Main filter capacitors replaced. The output transformer has the code - "BW", as in the amps above and below; and the choke - "AW". The mains transformer is a replacement. Back panel arranged originally as serial no. 337 (above).
Serial number unknown - probably in the 300s
Sold on ebay some time ago. Box in good condition. Grey panel, dome voltage selector, Woden transformers with unpainted shrouds, cathode biased - further capacitance added later in the power section (image 3). The original cathode biasing resistors and capacitors are still in place.
Serial plate unstamped - probably in the 360s - currently in the USA
Chassis no. 1055, but no serial number on the back panel. Cathode biased (which one can tell from the preamp tagboard); small upright choke; white Erie resistors; dome voltage selector; transformer shrouds unpainted. The red warning plaque is a repro. The amp now has a new reproduction thin-edged box, matching the repro 2x15" cab. The original box survives, however, in good condition (photo 1). Thanks to Donald for the pictures.
Note that the un-numbered serial number plate is similar to one that sold on ebay in 2007 (below). At this point in production warning plaques were normally white.
LATER RUN CATHODE BIASED AMPS
(second quarter / mid 1965)
In 2002, a fascinating discussion took place on VoxTalks about these later amps. The archive of VoxTalks is now defunct, but the discussion is available in this PDF - download here. "TedB" is Ted Breaux, the guiding light behind Jade Liqueurs (http://www.bestabsinthe.com/).
Serial number 370 - currently in the USA
An amp sold on ebay in September 2012 with this serial number. The serial plate is unlikely to be original to the chassis however - a number in the low 500s being more probable. See this page for further information.
Serial number 380 - currently in the USA
Chassis no. 1032. Cathode biased. Illustrated in J. Elyea, Vox Amplifiers, pp. 447, 449. Two further pictures added. Standard back panel arrangement - serial number plate in the centre, XLR and mains sockets centred vertically left and right, white warning plaque above the former.