Vox AC30 Solid State - late '70s

[kebab-eater]

Hi all,
Having come into possession of a non-working Vox AC30 Solid State, I thought it was a challenge too good to pass up. A lot of internets later, there really wasn't much out there. The only schematic I found looked like a photocopy of the one that is etched onto the back of the chassis, on a cover plate, and there are areas where even the original etched version is unclear.
So I bought a second unit. Then a third one. And a fourth. All had faults of some description. Here's what I've learned so far, in no particular order.
From voxshowroom: an entry in the 1977 UK product catalog, a half-page blurb with photo. No product write-up from Gary Hahlbeck though. Can't confirm his comment on the derivation of the circuit from Thomas Organ.
Nothing in Jim Elyea's seminal work on Vox amplifiers, nothing in Dave Petersen's "the Vox Story".
No published schematics or layouts excepting the schematic etched onto the chassis cover plate.
Reaching out to Korg UK produced "sorry we don't have any old papers any more".
Manufactured/assembled at the Dallas factory in Shoeburyness, Essex, from 1977 onwards, probably for at most a couple of years.
Features include the standard 6-way input jack array, a vib/trem facility with continuously variable speed control, switched using a wired-in stomp footswitch. Treble/bass on the brilliant channel only. (Tone) cut across all channels. No master volume. Exactly as was for the Later Dallas and early Rose Morris valve-based AC30s.
Uses a steel chassis in C-section, held in place using 6 machine screws through the upper rear cover, supported by two eccentric rotating wooden paddles inside the cabinet (no tray or side bolts).
The circuit is a lash-up of several different previously used circuit segments, in particular the use of two RC4136 14-pin ICs in the preamp section, and a derivative of a traditional single supply quasi complementary amp in the power amp section using 2N3055 transistors at the output. Capacitor coupled to a pair of 12 inch loudspeakers, which were either from Fane or Celestion.
Overall, the PSU is a fairly standard single supply using a hefty 1P1S transformer, 4x1N4007 to rectify and a single reservoir capacitor. Primary is fused on the top panel, secondary is fused internally.
Analysis of the serial numbers, including photographs from other units, suggest maybe 1000-1200 units manufactured altogether. Lowest number seen was 33028, highest 34070. No correlation with serials from any other product line by date or any other factor that I could see.
Earliest units featured the Dallas colour scheme for the top panel, plain grey with white lettering and piping. Later units moved to the Rose Morris colour scheme, with gold writing and piping over a different, darker shade of grey.
Most units had a single suitcase-style handle, a few had a single dog bone handle.
A very rare reverb variant (only two seen), with long tank in the cabinet base and an additional, small PCB to house the extra components, together with a small driver transformer. This made use of two unused op amps in the second RC4136. Serials dont match the range of the non-reverb units.
Several different versions of the main PCB were observed, including some with the "F" stamp, indicating supply by Faraday Circuits. All were single side, with track jumpers where necessary. Later versions had additional through-holes capable of receiving wires to support the reverb sub-system.
The main board contains the whole of the preamp stage, and the first half of the PA stage, the remainder of the PA components being mounted using an eyelet strip or directly on to the heat sink, which doubled as part of of the chassis cover. Jack array separately hand-wired, as were all pots and switches.
The cabinet is compressed board rather than ply, as it was for all of the Vox amps produced at that time. Tolex was the standard cross hatch. Grille cloth was what Gary Hahlbeck called the Rose Morris wide version, over black. No vents in the top, just the carry handle.
Overall, the amp has the feel of a poor relation (which I suppose it was!) of an AC30, using parts from a common parts bin, or the cheapest available.
No sign of marketing or sales outside the UK, although it's clear a few units have ended up in Europe.
If there's any interest, I will see if I can post up some gut shots, as well as scans of the chassis cover plates with the schematic etched.