13th August (2)
Further updates (still more to follow):
A series of updates:
Early solid state rectified
Further amps to come.
The page on amps with numbers in the 4000s has been recast slightly to take account of a group with a distinctive set of preamp capacitors - green TCC cathode bypass, WIMAs for the tone circuit, and large green Hunts 0.1uf coupling caps.
As a preliminary to arranging the early large-box valve-rectified AC50s in a more accessible way, an index of serial numbers, in order, and main characteristics will be posted soon.
Pictures of the band "The Amen" with a small box thick-edged AC50 Foundation Bass set in 1970 and 1971 now on the bands page (towards the foot).
A copy of an early 1960s Brimar brochure on the brimistor now available here.
A new page begun on the Celestion 18" speakers produced for Vox from early 1964 to early 1968 - at present the earliest types (1964).
Examples of later Celestion bass drivers will be added during the course of this week.
The page on bands with AC50 Mark 1s (two input and diamond input) has been overhauled.
By AC50 serial number 7400 we are into 1967. Amps have the logo adopted for the Vox solid state range, which was brought to market in April 1967.
By serial number 8168 we are well into 1968, and close to the end of JMI.
Most of the changes to the site have now been pushed through. The pages should be easier to view on mobile devices. A few tweaks to follow, but nothing of great note.
Next week, around 12 new AC50s will be added.
The general introductory page has been updated and will be adjusted further over the coming week.
There is some valid concern over who actually "designed" the AC50. The answer is JMI, but with a slight twist.
In the "Vox Story" it is said that: "JMI's design team was already fully committed in 1962 with the Continental organ and the various solid-state amp ventures, so Triumph Electronics, one of the AC30 chassis contractors, offered a 50-watt design based on cathode-biased EL34 valves. This featured two channels, each with its own tone circuit derived from the Top Boost circuit...."
Well there are unfortunately three misconceptions in that: (i) Triumph made AC4 and AC10 chassis, but not the AC30; (2) the AC50 was never cathode biased; and (3) the AC50 was of course at first single channel (in 1963 and early 1964).
Producing a cathode biased AC50 in any case would not have provided much advantage in terms of power over the AC30. A fixed bias circuit was needed.
It seems vanishingly unlikely that Denney, co-author of the "Vox Story", completely mis-remembered Triumph playing some part. Everything falls into place though if one sets the design of the fixed bias circuit at Triumph's door - i.e. the arrangement of lamp, diodes, and resistor/capacitor network.
The working prototype was made at JMI - the tone circuit certainly being the JMI Top Boost circuit - and sent to Triumph for copying, as Graham Huggett notes.
There is no doubt that Denney designed the AC80/100 himself. Cathode bias was his thing.
As a coda: you will find old talk on the internet of cathode biased AC50s actually being seen in the wild. They are unicorns, or yetis, perhaps both.
Above, a detail of the tone circuit of the AC50, and below it, the top-boost circuit of the AC30, designed in 1961 ("borrowed" by Vox from the Gibson GA-70).
The JMI top boost circuit clearly provided the model for the AC50 preamp. It is hard to believe that the latter was not created by Dick Denney at JMI (as has occasionally been claimed.)
The page on early AC50s in thin-edged boxes has been updated with new info.
The page on Triumph Electronics, makers of AC50 chassis from 1964-1967, has now been updated.
11th July (2)
A new page on an AC50 cab from 1966 with Goodmans speakers is now online here.
Some great info from Graham Huggett, who worked at Triumph from 1963 to early 1966. Graham was "chassis beater", making the chassis for AC50s on fly-presses and hand guillotine.
The prototype for the AC50 was sent from Dartford to Purley (Triumph was at 118 and 122 Brighton Road) for copying. Flat masters of the chassis were then made for production.
Around three people worked at Triumph full time. The wirers, mainly women, were part time and trained by Yvonne Andrews.
Control panels (bezels) were sent from JMI for the finished amps. Runs of around 50 chassis were made up on receipt of orders from Dartford.
Graham notes "assuming we had received the transformers from our manufacturer (took some weeks) the staff would easily wire up 15 chassis in a week." Testing was done with a meter, sine wave generator and scope, not with a guitar.
Triumph did not have boxes or serial number plates. The finished chassis were loaded into the back of Geoff Johnson's Ford Zephyr estate - Geoff Johnson was owner of Triumph - and driven by him, often at speed, to JMI.
There the AC50 chassis were given boxes and serial number plates added.
Graham had long-term loan of the prototype AC50 and used it for bass with his band for a couple of years.
The page on Vox Sound Equipment Limited AC50s - mid 1968 to early 1970 (though probably not quite that far) - now updated.
The page on Vox Sound Limited AC50s - from 1974 to 1975 - has been updated too.
The serial number plate of no. 1578 - fully hand stamped. Made by Triumph for Vox. Despite the relatively low number, the amp was made in October/November 1964. Two pots have the codes "HL" = August 1964. The others have "GL" = July '64.
Above, two adverts placed by Rudall, Carte and Co. in Crescendo Jazz magazine, the first June 1965, the second November. The first AC50 is a guitar amp, the other possibly a Foundation Bass. Rudall also had a Vox 80/100, perhaps an early one, in May '65. See this page.
1st May (2)
Pics of serial number 3088, valve rectified, assembled at the Vox/Burndept works, now registered here. It seems likely that Burndept was simply using up available chassis as they came to hand - and this one, in company with serial no. 3226, happened to have been made for the old valve rectified circuit.
Some pages on early large box amps now updated, esp. those for amps with serial numbers 2000 - 4000. Further updates to come.
30th April (3)
A shot of the Goodmans catalogue page for the Audiom 90 - the first British 18" driver produced - used by Vox in the earliest Foundation Bass cabs (in its slightly later 15 ohm version). £28 in early 1964 is equivalent to around £520 in today's money. These were not cheap.
30th April (2)
Three new AC50s from the third quarter of 1964 added on this page, along with some updates to the intro. The amps in question have serial numbers 1729, 1746 and 1763. None preserves its original voltage selector, however.
22nd April (2)
Been a little while since the last series of updates - a good amount of new material to be added now over the coming days.
Serial number 118x - small thick edged box, diamond input - on sale here.
Click for a larger image. The Vox Solid State catalogue from mid 1967 - still the AC30 and AC50. The AC100 is not depicted, though it does appear in the contemporary pricelist.
28th January (2)
An early Thomas Organ flyer for its new solid state range, the "Berkeley" clearly styled after the large box AC50. The format was later changed. The blurb reads:
"High quality amplifier incorporating variable length reverberation and multi-speed variable depth vibrato. Two inputs, separate tone and volume controls. Amplifier and loudspeaker units are in separate cabinets to give greater power with feed back."
28th January (1)
"The Others and Me" with their large-box AC50 guitar amp, and thin-edged Mk1 Foundation Bass. The Mk1 amp is visible behind the bassist, Gary Thain, in the pic. below.
"Country Pie" in the early seventies with a thick-edged small-box Foundation rig, a large box AC50 and Vox Conqueror.
21st January (2)
A late Vox Sound Ltd advert for the AC50, still the Foundation Bass, the guitar version with a new cab (closed back and deeper than normal) and trolley, which might have benefitted from better styling.
21st January (1)
Above, "The Rapiers", from East Anglia, on stage with a small box AC50 and T60 cab. Picture originally posted here. Note the position of the logo on the amp - middle left, rather than top left, as in the amp below.
The amp from this set is now in Brighton, the cab in London.