Datasheet in PDF format for the 2N3055, 179 KB, filed among schematics; the RE suffix in the name is not explained and may mark a revised or reissued copy. It documents a widely used 2N-series transistor, giving ratings, curves, safe operating area and case outline. On the bench it helps confirm a failed part and the correct pin assignment before fitting a new one. Open it in any PDF reader and compare with the other 2N3055 sheets in the index, which come from different sources.
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.
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The standard format for schematics, block diagrams, power-sequence charts and service manuals.