Here are some of the vacuum-tube operational amplifiers that form our heritage:

1. Loebe Julie's 1941 vacuum-tube operational amplifier with differential inputs.
   
   
2. 1942 M-IX Gun Director Operational Amplifier (which needed 5 precision regulated power supplies).
   (printer version)
   
   
3. 1950-era operational amplifier for Nike Missiles.
   
   
4. Data sheet, Philbrick K2-W. (page 1, page 2)
   (printer version:  page1,  page2)
   
   
5. Expanded Schematic Diagram, Philbrick K2-W.
   (printer version)
   
   
6. Data sheet, Philbrick K2-XA. (page 1, page 2)
   (printer version: page1, page2)