... Is there a good source for schematics and service info ?
For as long as I can remember, there has been a publishing service,
Sams Photofact, that sells service manuals, schematics, etc. for almost every make and model of TV, radio, and phonograph available in the USA. Google that phrase and visit my link. Back when there were still Radio and TV Repair Shops, you could purchase a Sams subscription and get periodic updates when new models were released. Here in Dayton OH there was an electronics parts supplier, Stotts-Friedman, who catered to Radio and TV Repair Shops. They had several file cabinets full of Sams Photofact folders (usually there were several different makes or models in each folder) from which they would sell individual folders... good luck if someone had already purchased the folder you needed, because then it would have to be ordered resulting in several days or weeks delay getting the service information needed to make a repair.
Unlikely as it would seem with the disappearance of mom and pop TV service, along with our "don't fix it, buy a new one" economic model, Sams still exists and is still providing Photofact folders which you can now order on-line, no subscription required. They will also contact manufacturers on your behalf to try to obtain service information for products that don't have a Photofact folder. I haven't used a Photofact folder since the late 1960s, but that is where I would try first to obtain schematics and service info for guitar amps, especially vintage vacuum tube amps. You could of course try to contact the OEM (Original Equipment Manufacturer) yourself to see if they can provide what you need. Good luck with that.