I’ve recently purchased a copy of Merlin Blencowe’s book “Designing Tube Preamps for Guitar and Bass”.
This is the best books I’ve read on guitar amp pre-amps, which will come as no surprise to anyone who has visited Merlin’s excellent website. Although the approach is quite academic, even if you aren’t into the maths (sad to say I am), there are a ton of useful ideas and practical tips.
Thoroughly recommended.
The only disappointing feature of the book is that the author chose to you “tube” in the title rather than “valve”!