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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