I picked up RG Keen's "Vox Owner's Safety Net" recently for some background info on a Thomas-Vox Beatle that came across the bench. The book has a clear breakdown of the various circuits used in the Thomas Vox amps. What I wasn't expecting however was a really great section on debugging transistor circuits in guitar amps. Even if I never work on another Beatle amp I'm going to keep going back to the transistor debugging section of the book. I can't recommend the Safety Net book and the various supplements highly enough, especially if you have to service one of these amps.
http://www.thomas-vox-repair.com
RG Keen's Thomas Vox Books
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