Like several previous pickups, the 513 pickup was produced for Hofner by Franz Pix. Although widely described as a Hofner 'Blade' pickup, it is generally described in Hofner literature as a bar pickup or all-sound pickup. The blade itself was originally un-nothched - see the image from the 1967 and 1968 Selmer catalogues - however, certainly by early 1968 the notch was present. It may be that differing versions of this pickup exist, as the catalogue descriptions mention two coils (i.e. a humbucker) but many people who have disassembled them have found just one coil.
The following description comes from original late 1960s promtional material
Number 513 model "All-Sound", metal box with small plastic frame, adjustable in height. Two layerwound magnetic coils, two permanent magnetâ€“systems. One pole with individually adjustable magnet screws for each string. Especially true to nature reproduction over the whole range of frequencies of the guitar.
And from the July 1968 Selmer catalogue:
A brilliant new pick-up design by Hofner, which gives excellent response over the whole tonal range. The bar magnet provides equal balance on all strings and eliminates the overpowering second string sensitivity found in conventional pick-ups
The unit pictured below has a DC resistance of 8.17kΩ
List of Hofner guitar pickups