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by Rich Rarey
((PUBLIC DOMAIN column for October 1995 Radio World, reprinted by permission))
Display the recipe to clean tapes of Mold
| Our Readers Respond... | We've received engaging
E-Mail from several readers for our "Bake the Flakes
Back into the Tape" column of several months ago.
Greg Guarno asked us 1. What are the audible
effects of 'baking' the tapes? I have heard that it
dramatically increases 'print through', and that it may
erase some of the high frequencies. |
|
I posed these questions to our two tape experts: William Lund, senior technical service engineer at 3M, and to Tom Neuman, senior staff engineer in charge of the Recording Technology Group at Ampex. Both experts said baking tapes at the prescribed temperatures will have no apparent audible effects. Neuman says a temperature at 120 degrees F does not affect lubricants or other additives, it does not destroy splices, plastic reels or leader materials. He adds that after personally baking 2,000 tapes, he has not noticed any adverse effects. Lund says that high frequencies do reside nearest the actual surface of the tape, but unless that surface is disturbed in some way, the baking process does not change the magnetic properties of the oxide particles which make up the magnetic coating of the tape. In Tom Neuman 's opinion, the only risk during baking would come from stray magnetic fields inside the oven from the electric fan motors, heating elements or solenoid coils. He adds that it's a good idea to check for any such stray fields before baking a tape in an unknown oven. |
| What is print-thru? A definition | Print-though, according to
our old Audio Cyclopedia, is the "unwanted transfer
of a signal from one layer of tape to another by magnetic
induction". According to Bill Lund the print-through
phenomena is also not well understood and even more
elusive to quantify. He says it is a characteristic of
the oxide used and how it is prepared for use in the
chemical binder of the tape. Interestingly, print-through
reaches a "terminal value" after a period of
time. That is, the tape will achieve the most print-
through it can have, and the amount of print-through
thereafter will not increase. The time it takes for a
tape to reach this "terminal value" is
dependent on the tape (and the oxide used on it) and the
storage temperature. Lund says that since the oxide and
the tape are pretty much fixed, the biggest variable is
temperature. A tape stored at a very low temperature will
take a considerable time to reach it's terminal value for
print-through, whereas a tape stored at high temperatures
will achieve it's terminal value much more quickly. The
terminal value is the same in both cases, it just takes
much longer to get there at low temperatures. He advises not to worry about the 'baking' process and it's potential for causing harm to the valuable tapes, because it doesn't happen. |
| What's different now? | What are Ampex and 3M doing
differently? Tom Neuman says that when the sticky
shedding syndrome was first noted and the effect fully
understood about nine years ago, ALL tape manufacturers
began the process to improve the tape's archival
stability. Bill Lund points out that "you do not
build a new binder and chemistry overnight", but
rather attempt to design new tape stocks with greater
longevity. He points to 3M's 900 series of tapes as such
an attempt, but cautions that even with all manufacturers
using accelerated aging tests to predict the behavior of
their product, the outcome is still...a prediction. The binder problem did not appear until 7 or 8 years after introduction of the product, and since predictions didn't show the problem at all, Lund says it "hit us as a real surprise". One interesting aspect of a particular product's age, Tom Neuman points out, is that manufacturers don't have control over the age of tapes sold by some of the supply houses around the country. A reel purchased 5 years ago could actually be 8 or 10 years old. Neuman recommends buying tape stock from well known and reputable distributors, and avoiding garage and surplus sales, where, he says,"nobody has any idea of how the tape had been stored or the actual age of the tape." |
| Bring back the old tape formulation -NOT! | Why then, with all the excitement over binders becoming unbound, don't the tape companies return to the old tried-and-true formulations that worked so well? 3M's Bill Lund says that in the quest for tapes with higher output, lower noise and lower print- though, different oxide technologies were required. The modern, better-performing oxide formulas are chemically incompatible with the older binders from 40 years ago. Consequently, if manufacturers were to return to those old binder compositions, we'd see a return of tape stocks that had inferior print-through, maximum output, and bias noise floors. |
|
Neuman says he has personally cleaned dozens of tapes using this method and it seems to work quite well.
We wish clean, dry, securely bindered tape to you all.
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| Author's note: Since these articles were
published in 1995, the tape industry has changed
dramatically; 3M no longer manufactures recording media,
and the division of Ampex that made recording tape has
been spun off, and is now known as Quantegy. Bill Lund is
working with 3M in their commercial graphics division.
You can reach him at wflund@mmm.com,
or at 75763.2162@compuserve.com.
Tom Neuman has left Ampex and is persuing interactive media development. You can reach him at Wildware@aol.com Interestingly, Bill Lund says Quantegy has recently purchased 3M's recording media intellectual property rights and remaining tape stock. |
Rich Rarey a Technical Director for National Public Radio, and can be reached at rrarey@npr.org
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