Magnetic tape viewer

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(03-05-2020 09:17 PM)Jake Schwartz Wrote:  … in the 1970s, there was a liquid version of this viewer, called "Magna See" which did the same thing … decoding the HP65 and HP67 instruction sets by applying the liquid to visualize the tracks on the mag cards …

Magna See is referenced twice in Magnetic Recording Handbook:

Bibliography and References
page 639. Magna-see. Reeves Soundcraft Co., New York, N.Y.

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Bibliography and References
page 715 Magnasee, 29
MAGNETIC RECORDINGS MADE VISIBLE
The theory just discussed is verified dramatically by actually rendering a tape recording visible. When iron filings are sprinkled on or adjacent to a magnet, the particles align themselves to show the magnetic field direction. In the same way magnetic recordings, though much smaller, make themselves visible by attracting microscopically small particles under the proper conditions. The results are favorable when the particles are of micron size in a dilute liquid suspension. The finest grades of carbonyl-iron are suitable for the particles. Petroleum naptha is suitable for the liquid, as it dries quickly and is relatively nontoxic. The mixture is shaken vigorously and a few drops are flowed on to the surface of a magnetic record. Patterns of the recorded tracks develop out in a few seconds. Contrast improves after the liquid dries by evaporation. The pattern may be preserved by spraying with varnish or lacquer, or it may be wiped off with a cloth without harm to the recording. An alternative procedure that gives more uniformity is to dip a strip of the tape into the suspension for a short time, shake off the excess liquid, and allow to dry face up. Proprietary mixtures like the above are sold under such names as "Magnasee" (Reeves Soundcraft Co., New York, NY). Figures 2-10 and 2-11 show the patterns around wire recordings and tape recordings made visible by these techniques. Colloidal suspensions of much finer particles may be prepared to bring out detail according to Bitter techniques by which magnetic domains were first discovered.

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