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Re: [ARSCLIST] Ampex 456 and Shamrock 041 Manufacturing Specs?

Tom Fine wrote:
3M also had cheapo "Highlander" brand tape for a while. I'm not sure if that was stuff that didn't meet spec or if it was 3M's last generation of brown-oxide, no-backcoat duplicator grade tape.

My experience with olden days Shamrock (brown-oxide acetate and early polyester days) is that it's not destruction-prone like some tape of that vintage but it usually country-lanes all over the place . . . Just what did a batch of tape have to do to get badged Shamrock instead of Irish?

I have no answers, only a bunch of urban legends.

1) The tape might have been the outside slits from the original 18-inch wide rolls -- that the regular grade tapes were the ones in the center. That might mean the oxide was full grade but they didn't trust the slitting. Or maybe the oxide might be thinner towards the edges.

2) These were the short ends of the rolls and are made from two shorter parts spliced together. I remember that some tapes seemed to have a splice about 2/3s of the way into the reel. Remember that most full-grade boxes mentioned that they are "splice-free". The tape might be fine but might change specs at the splice!

3) The slitting might have been bad. I have one reel I bought in1965 that is slightly too narrow. In 1967 one of the prolific producers at our station bought three or four reels that were slightly too wide and wouldn't play on the two home-grade Ampex machines in our main air studio. The tapes would just stop dead because these had the self-thread guides the full width of the tape slot. Unfortunatly, before we discovered this, he was assembling dozens of shows from things done on different reels of tape, so a segment on almost any of his shows might have come from those wide reels. For the rest of the year we had to run any of his shows from a machine in one of our other studios and patch it into the air studio board.

4) These were computer tapes that didn't make the specs for computer tapes but would be just fine for audio when they slit them down from 1/2-inch. This was the rumor especially when the highly polished oxides started appearing. Of course computer tapes needed different bias levels than audio machines and were designed for different wavelengths than audio. Then came the rumors these could be slit videotape. That would be even worse since the oxide particles might have been optimized for the different azimuith angles.

5) The black oxide backcoated tapes were 456 that didn't meet specs but were still better than regular grade tape. Oy veh.

6) The graphite lubricated backcoated tapes didn't meet the grade for tapes for cartridges. THIS, I believe. Whenever I got a reel of this, I set it aside to rewind carts. I don't think this stuff wore well.

Why oh why oh why did we buy this crap?? Because we were starving students or poorly paid professors, etc. And now we get that vicarious thrill knowing that those who could afford the GOOD stuff are having the same or worse problems now that we have with the crap!!!!

Mike Biel mbiel@xxxxxxxxx

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