The first time you take a vintage piece apart, you may be shocked at the simple quality and small diameter wires you find.
Keep in mind, this is within the pieces that produced results that made the reputations of these great companies.
You mentioned amps, but I will never forget what I found inside the Fisher/Electro-Voice speakers I inherited, (made in 1958)
The wires looked just like these:
http://www.fisherdoctor.com/ev.html
just came across this tidbit
"They decided to focus their business on audio products. The company designed a PA system for Notre Dame football coach Knute Rockne. Rockne, who had difficulty being heard at football practices due to health problems that affected his voice, called the new PA system his "electric voice". Rockne’s remark inspired the company’s name. On June 1, 1930, Burroughs and Kahn incorporated under the name "Electro-Voice".[2][3]"