Fisher
Fisher 400 Tuner/Amplifier Service Manual (scan 1, scan 2)
Harman Kardon
Citation II upgrade (DC restorer) by Stu Hegeman (page #1 and page #2)
Pioneer
Pioneer SM-83 Integrated Amplifier Schematic Diagram (scan 1, scan 2)
Sansui
AU-70 Integrated Amplifier Schematic Diagram (PDF)
AU-111 Integrated Amplifier Sansui AU111 Schematic Diagram (PDF)
BA-303 Power Amplifier BA303 Schematic Diagram (scan 1)
Russian Vacuum Tube Testers
L1-3 User Manual and Schematic (DJVU Format)
L3-3 User Manual and Schematic (DJVU Format)
Articles
Measuring Unknown Choke (PDF)
Final Touch for Your Amplifier, by Harold Reed (DJVU)