VOX AC30 TOP BOOST

I recently brought this VOX AC30 Top Boost the casing beeing absolutely mint with cover and even a manufactures tie on tag still on the handle. One previous owner from new. Unfortunately a previous repair left it with a Dynacord mains transformer, most of the switch contacts on the old jack sockets open, the vibrato channel diddint work at all, the main problem beint that the 25uF cathode capacitor had gone short circuit causing the 220K to go open circuit due to excess current being drawn. In fact all the cathode capacitors needed changing and most of the old resistors were well out of specification. There must have been quite a burn up around the rectifier (GZ34) socket and generally the underneath of the chassis. At least the main HT capacitor hadbeen changed, possibly being the original cause of the burn up of the rectifier socket and mains transformer needing replacing. The filiament wire had gone brittle with age and several other wires needed replacing, the 100R screen resistors and the 1K5 grid 1 resistors were the wrong value. Then found that the 110 volt tap didn't work on the voltage selector after replacing the mains transformer with an original AC30 old stock mains transformer so the voltage selector was also changed. The vibrato adjustment pot was broken to an old stock pot was fitted. There was a crackling problem on the top boost circuit due to a bad B9A valve base which also needed replacing. It's a good thing that restoring amps is my hobby, cause after this the clean up of the chassis took about 10 hours, moving certain tag blocks and components, cleaning with steel wool and the metal polish. Anyway check out the photo's of before and after. Hopefully this will make it clear to people that fixing an old amp is not just fix the fault like on a modern amp but virtually a complete rebuild if you want reliable operation with the amp working reasonably in specification. Resistors generally increase in value and even go open circuit with age especially if they are working close to the limits of their spec, Electrolytic capacitors need replacing as the electrolyte dries up causing them to eventually short out and it is always a good idea to change critical capacors such as the decouplers to the output stage with high spec polyprop 1000V capacitors and it is a good idea to replace the capacitors in the vibrato oscillator circuit. I guess if I added the time up done over a period of this restoration project must have taken nearly a week of effort in total.

Various Chassis views

New capacitor

Mains transformer from an earlier Vox AC30 so still an original Vox AC30 mains transformer even though it is from another older Vox.

Some new capacitors and a lot of resistors changed

Another New electrolytic capacitor and note the 2 fairly expensive replacement polyprop capacitors for decoupling of the output stage from the phase splitter

Heat resistant sleeving on the HT wiring to the output transformer and the 4 XEL84 output stage.

New cathode Capacitor and resistor. The early AC30 amps used a cathode resistor of 82R but in the mid 1960's changed to 47R. It is quite interesting to note that (other faults permitting) generally the older amps have less wax deposited from the mains transformer getting hot. In fact the mains transformer runs a lot cooler with the earlier valve of cathode resistor.

New valve base for the GZ34 and new 100R resistors on the output stage

Just how many AC30's made sometime in the 1960's still have the original manufactures VOX tag still tied onto the handle. One original owner kept from new in it's cover.

Front cloth perfect condition