For newbies and even some of us 'Seasoned' techs. He covers a great variety of important tube amp tricks and concepts just repairing and modifying this signal tracer.
Search YouTube: 'Electronic Repair Adventure- 'The Signal Tracer'. Mr. Carlson's Lab.
He also rebuilds a Fender 135W combo amp from a technical standpoint although he's not a musician and does it from a non-musician standpoint. (I haven't watched that one yet).
He does alk this in a very understandable-down-to-earth manner. Glen