Take the advice of TerraHertz and nctnico. Read the schematics from the published service manuals of older test gear. Lots of great insight and reliable, proven designs there.
Check out magazines, hunt for pdfs if you have to, and read those instead of random blogs or random aggregations of schematics on websites. Many of the schematics you'll find on random websites just aren't right. They have poor input protections, or filtering, or limited usefulness over temperatures... or various corner cases, and have really not been well thought out, and you will only learn to repeat their mistakes if you follow the examples of most of what you find on the web.
So trust the magazines (although they are not always the best either) and trust the old service manuals. You'll learn far better practices from those sources than anywhere else.