A Vox Ac30 CC2X arrived that was sounding mushy, crackling and popping and when you tapped the case made wonderful microphone !
On removing the back it was obvious that the EL84’s had been in the amp since new and I guess the amp to 5 or more years old. One of the ECC83’s had been changed for Groove Tubes at some point.
On testing the EL84’s they were totally mis-matched to each other and one ECC83 was weak and the other totally microphonic.
I fitted a matched JJ ECC83S in the phase splitter position and put four new Sovtek EL84’s. They run with lower current than what was fitted. The V1 position now had a Tung Sol 12AX7 for a nice rich tone and being tested at the factory for microphonics would ensure the microphonics would not return again.
I gave the valve printed circuit board a good clean and degrease as it had a lot of dust on it. This can cause possible leakage currents if not cleaned especially around the pre-amp valves.
The pots and jack sockets had a good lubrication and were cleaned to keep them nice and quiet. It was PAT tested to make sure it will plate the owner through bad earthing
Finally the amp was tested and played. The amp sounds really good and I liked the sound of the Celestion Greenback speakers. sadly though the reverb in an AC30 just does not have the sound of the Fender amps. However in every aspect this amp really deserves its reputation as one of the all time classic amps. It sounded lovely and sweet and ready to rock at more gigs !