I've been repairing valve and transistor amps (on and off) for thirty years. I'm a Chartered Electrical Engineer with 20 years experience in the Electronics industry. I've got a masters degree in electronics, but if you know anything at all about valve amps you'll know this is not that important. I can do anything from a service to a complete rebuild. I can do modern amps but generally you're better off taking them to dealers. I do guitar electronics - pickup and switch replacement, rewires etc. I am not a Luthier so please do not ask me to cut holes in your instrument.
I like Ampeg B-15s. I import them from the States and service them and have their transformers rewound for use on UK mains. I usually have one or two knocking around, so if you want one get in touch.