Combined datasheet in PDF form covering the LM138 and LM338, 396 KB in size. Both are adjustable positive voltage regulators rated for around 5 A, the LM138 being the wider-temperature grade of the same design. The document should give the pinout, the resistor formula for setting output voltage and thermal limits. Technicians use it when repairing bench supplies and power stages, to verify adjust-pin voltage and confirm resistor values. Check the package and pin order on the actual part, as TO-3 and TO-220 versions differ.
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 @cyberlanelectonik. 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.