Schematic for the 60 W NDFL amplifier published by ETI in 1983, combined with a regulated power supply, in a 6.74 MB PDF. NDFL is generally read as no-negative-feedback-loop, but rely on the document text for the exact topology. A size like this usually indicates scanned magazine pages with the circuit, layout and constructional notes. Use it to restore or build the amplifier, and check how legible part values are in the scan before ordering components.
The button opens the matching file on RM Schematics, or a source page if it is not catalogued there yet. The original attachment is from @pdf_servicemanual. Enginerys does not host this file.
How to open a .pdf file
The standard format for schematics, block diagrams, power-sequence charts and service manuals.
Any PDF readerSumatraPDFFirefox / ChromeFlexBV (links PDF to boardview)