This amp rebuild uses the Vox AC30 TBX UK made 1994-2004 series speaker cabinet and integral head chassis as the starting point. All electronics and transformers are discarded from the amp head (some of these, notably the Drake output transfomer, were reasonable quality but were rejected in favour of higher quality components and transformers throughout), and the steel plated head chassis is then cleaned down and drawn up for drilling of mounting holes for valve sockets, larger choke and tagstrip mounts.
The whole amp head is rebuilt from scratch using custom designed handmade mains choke and output transformers, over rated resistors, and preferred coupling and electrolytic capacitors all hand soldered on tagstrips like the best of the 1960s and 70s AC30s were. The circuit is my tweaked version of the AC30 based on my own preferences from the 1960s and 1970s amps along with a few custom touches thrown in.
Version 3 with silicone diode rectifier:
Silicon Diode rectifier used on the Brian May/Fryer AC30s:
With the version 3 Brian May AC30 I have used a small tagstrip for the 1N4007 silicone diodes. The tagstrip is mounted on 2 standoffs which bolt directly into the TBX chassis holes for the removed GZ34 octal socket. In the photo below the small rectifier tagstrip is at below right.
1N4007 tagstrip above here ^
‘Ultimate BM AC30′ debate? Well, many might say that Brian is using them already! I will put up a schematic diagram here soon, you just get rid of the things that I put on Brian’s 3 amps that were there to fill up the extra holes in the Vox top faceplate – such as the master volume control/ switch, 2nd normal channel with its vol control, and that luvverly Aussie sixpence.
Things to have:
Silicone diode rectifier as in the above pic and diagram, custom made Mains Tx old style full layer even wound like Martin Kell made for my amps’ mains txs, wound for 300-0-300 (not 310-0-310 like Martin’s txs, he based this on some of the best AC30s that he had seen from the 1970s), custom wound output transformer like Paul Voller’s and good to not to have modern mass produced transformers in my opinion, old style JMI choke not the choke filtered whole B+ supply idea like the DP amps, 2-4 EL84 switching this can be really good at times, definitely keep the EL84 cathode fusing and LEDs – this is really useful when an EL84 goes AWOL, Leo Fender style standby switching from above diagram rather than Grindrod style TBX style standby, 330 ohm/3W metal oxide resistors for EL84 screen grids, all valve sockets chassis mounted of course, all components hand built on tagstrip or turret board, thats about it…ready to rock!
No Matchless style master volume is needed of course, no master volume control ever really does the job soundwise compared to running the amp hard but a Mayday pedal would be a very useful addition in the guitar arsenal pedal suitcase 😉
More ideas and diagrams soon, GF