Much of Shamrock 0XX series tape was reslit computer/instrumentation tape, or govt spec tape made by Ampex that didnt meet spec.
Thats the reason for the various oxide and backing found from reel to reel.
The 1.5 mil black oxide with/wo back coating was computer stock, used by main frame computers for data storage. This was original 1/2 x 10" stock.
1.0 mil was instrumentation tape, usually after being used for one pass date downloads. Govt policy was not to erase tape, use new to avoid any contamination of new data by previous data that didnt get erased.
The navy contract was mostly for brown oxide in 1/4" audio formats on 10"plastic reels.
.5 mil with shinny black oxide was from 10"x1" or 14"x1" instrumentation tape. This shinny tape often lacked low frequency response as in instrumentation use a 15/30 ips tape speed was used and the data stream didnt hold any lo-freqs.
How do I know this? I worked for DAK industries buying, grading, overseeing the resliting operation with stock from the same sources used in much of the Shamrock product. We often bought Shamrock over stock and reboxed it as DAK tape.
In the early tape days nothing went to waste... there was always a use for bulk stock and bargain hunters who wanted something to talk back to them at a bargain price.
The laugh of the industry was a certain tape coater in Los Angeles that would buy the surplus Mother Cookies cellophane bag stock with the purple Mothers printing on the back side of the tape.
Ahh the fun days of long ago.
--- On Sat, 2/21/09, Michael Biel <[log in to unmask]> wrote:
> From: Michael Biel <[log in to unmask]>
> Subject: Re: [ARSCLIST] Ampex 456 and Shamrock 041 Manufacturing Specs?
> To: [log in to unmask]
> Date: Saturday, February 21, 2009, 9:53 PM
> Sarah Norris wrote:
> > Hello,
> > I'm looking for any manufacturing information
> available about Ampex 456 and Shamrock 041 tape. Anything
> would help, including manufacturing dates and anything known
> about materials or formulations used. All information and
> references are much appreciated.
> > Thanks,
> > Sarah Norris
> These were made in the former Orradio Irish Tape factory in
> Opelika, Alabama which Ampex bought in the early 60s.
> Shamrock 041 is 1 mil, 031 is 1.5 mil, and 051 is 1/2 mil.
> Shamrock, also found in Radio Shack Concertape boxes among
> many other brands, came in many different varieties. You
> could find brown oxide, standard non-backcoated black oxide,
> polished black oxide with carbon backcoating, and brown
> oxide with lubricated graphite backcoating that was normally
> used for winding continuous loop tape cartridges. When the
> boxes were shrinkwraped you had no way of knowing what you
> would get. I used to buy shrinkwrapped Concertape in
> discounted quantities of 10, and never did I get ten of the
> same type! In the early 70s I used to go to the main
> mailorder warehouse of Olson Electronics in Chicago which
> let me go thru the factory cartons of un-shrinkwrapped
> Shamrock 041 and pick which reels I wanted if I bought them
> in multiples of 50. Types were mixed in every one of those
> factory cartons of 50. Unfortunately I went for the quality
> stuff -- black oxide carbon backcoated. DAMN. So thre is
> nothing consistant about the 0X1 series.
> Mike Biel [log in to unmask]