Mid-run cathode biased amps
AC80/100s in thick-edged boxes
Black panels (late 1964 - early 1965)
This page is a small gathering together of info and pictures relating to AC80/100s with black panels, some of it repeated on this page.
Perhaps the main question arising is whether every amp in the serial number range in view (from around 230 to 310) had a black panel. It certainly seems likely from the spread of survivals registered below.
A number of changes evidently accompanied the move to black panels:
- Transformers (still made by Woden) have plain metal tops instead of sea-green coloured enamel. Their date codes are of late 1964. See this page.
- The Type 1 trolley, with a basket top for the amp to sit in, gives way to the Type 2, with parallel bars across the top. An overview of early trolleys is given on this page.
- Main filter capacitors (100uf, 500v) were sourced from Daly late in the black panel run. The smaller ones came from TCC - the Telegraph Condenser Company. Information on various components is being gathered here.
The chassis of serial numbers c. 230 to around 300 were made for Vox by Westrex, which was based in north London. A small run - a few amps with serial numbers in the low 300s - was subsequently produced at the Burndept / Vox works on West Street in Erith. The West Street works became the main centre of production of AC80/100s in early 1965.
As ever, if anyone knows of other cathode biased amps with black panels, please email me at click here for the address.
Serial number 236 - currently in the USA
Perhaps the original cabinet (ie. the one that accompanied the amp from the factory) - note the Type 2 trolley. The original speakers have gone, but some of the wiring loom is still present. The layout of the back panel is much as that of serial number 262, below.
Serial number 249 - currently in the UK
Sold recently on ebay.uk. In company with serial no. 262 below, this amp has a Bulgin mains connector set low on the backboard. Speaker XLRs have been replaced. External condition is good.
Serial number 262 - currently in the USA
Below, an earlier picture of the amp in its original box and before refurbishing. Note the pattern of wear on the replacement output transformer. Between this picture and the ones above, the mains transformer, which is attached to the chassis upright with a bracket, must have gone.
Its existence was reported by "Joe L", its owner, in 2005 in a number of threads on the Plexi Palace Vox board in 2005. The relevant ones are here and here. The amp evidently had a fire at some point, damaging the power tagboard. Joe L also notes that the control panel was black, and that the Midax horns survived - presumably from the original cab.
The original box is not present - the amp now lives in a thin-edged North Coast Music reproduction thin-edged case. Mains and output transformers are replacements, and the power section has been restored, but chassis and preamp are fine.
Note that the shroud from the mains transformer survives, though has been turned by 240 degrees (in relation to the metal bracket fixing). The date code is KV = October 1964.
Serial number 269 - currently in Finland (collection: Björn Schauman)
Black panel. A single owner amp. Bought new by him in 1964/1965 along with a 4 x 12 cabinet. Used in the Finnish band "The Slippers", who were from Vaasa. Google translate, alas, only makes only partial sense of the entry for the band in the Vaasapedia. The amp is still in working order. Note that the white warning plaque, if in its original position, is in a non-standard position.
Serial number 276 - currently in New York
Sold on ebay in March 2006. A nice example of a black control panel. Probably very late 1964. The box has two fixing points on the top edge of the back panel.
Acquired by the previous owner (Connecticut) in 1993 from a seller in Washington State. The underchassis had been rewired, and the grille cloth and back panel connectors replaced (the cloth by Thomas Organ cloth). Put back as far as possible to stock by the previous owner.
Serial number unknown - currently in the UK
First eight pictures, the amp on ebay in 2007.
Resident for many years in Germany, this AC80/100 evidently saw plenty of action. The box is not original to the amp (note the stamping "G-R" = the Gla-Rev company). The internal wooden runners and fixing holes do not correspond to the chassis. The warning plaque may have been transferred from the original case, however.
Probably in an attempt to keep heat down, the chassis was painted black at some point (transformers and preamp upright too). One can see in the pictures below that the transformer shrouds, where the paint did not reach, were originally either green or tarnished bare metal - most likely the latter.
Note that the rough holes in the aluminium by the input jacks do not appear in the present control panel. The panel is therefore likely to be a replacement, possibly a relatively early one, replacing the original black.
Capacitor codes are VJ and VK = September and October 1964. The original 270ohm cathode resistors are datable to September 1964 too (they have the codes VK). The amp is therefore likely to have been produced in late 1964.
The mains transformer was removed in Berlin in 2006/2007 and replaced by an unsuitable unit, itself now replaced.
Above, a transformer from a Mk2 AC100, varnished by Majestic Transformers in Poole, in the course of being fitted. The original filter caps were made by Daly.
The amp as it is in 2014. The cathode resistors and capacitors were too far gone to use unfortunately, so have been replaced (and kept). Due to the higher B+ of the transformer, the present resistors are 390R, which is the lowest the valves will take. The jumbly connectors have now been replaced with ones more appropriate to the amp.
AMPS PRODUCED IN THE BURNDEPT FACTORY
Note the machine stamped serial numbers and the standardised layout of the back panels. For amps of the same date with grey control panels, see this page.
Serial number 306 - currently in Italy
A really fantastic AC80/100 and speaker cab. Black panel. Just visible through the grille, the large "lay-down" choke. Original XLR and Cannon LNE32 mains connectors on the back panel. Note the rivets (?) around the rims of the silver Celestion T1088s. The box has a single centre fixing point on the top edge of the back panel. Thanks to Tommaso for the pictures.
Serial number unknown - currently in Austria
Sold on ebay in 2007 and perhaps again in 2009 - it seems very familiar. The amp now lives in a later box with a three-line serial number plate = late 1965. The original serial number is unknown. The speaker cabinet and trolley may be of the same date as the amp's box. Note the unpainted Woden transformers (in the last image) and the dome voltage selector, the former as in no. 306, above.
Serial number 330 - currently in the USA
Reported as having a black panel (no pictures available at present). Note that serial numbers 320, 328 and another amp with a number close to 300, have grey panels.
A DIGRESSION - later black panels - 1967
Three black control panels of a different sort are known: on two AC100s, and on an AC50 probably put together by Alan Pyne.
The letters JMI are contained in small outline boxes, and the legend "WARNING" is off-centre in relation to the indicator lamp.
1. Accompanying an AC80/100 box - currently in the USA
Posted on a Plexi Palace thread, September 2009 - link here. The amp inside the box conforms to the "100W amplifier" schematic, probably having a serial number in the 600 or 700s, and is registered here.
2. AC100 seen at the Vox Factory, Dartford Road, in 1967
A black panel seen on an AC100 at the Vox Factory during the closing down sale in 1967 - reported on this page.
3. A sort of AC50 in a thin-edged box
Probably assembled from left-over parts by Alan Pyne, who took over the old Vox premises at Dartford Road. The green Woden mains transformer, similar in style to the transformers used in AC80/100s, but with a 5V line for the rectifier valve, has so far not been found in any other amp.