From: "Glenn Meadows" 

The 1973 tape was a totally different problem.

In the late 70's, into the early 80's, formulation of tape was rapidly
changed due to EPA demands.  The old stable formulations of tape had to be
changed to remove carcinogens released during the actual manufacture of the
tape, and both Ampex and 3M were give 90 days to make changes, or stop
production.

That lead to shortages of tape for about 9 months, as each company
scrambled to adjust tape formulation and mfg procedures that had been
tweaked and micro tuned over years of production.  The initial new
formulations appeared to work well, but about 12 years later, a horrible
problem appeared in tapes made during the first 3-4 years of that span, the
binders started to break down due to absorbsion of moisture, and what was a
solid coating, started to turn to gooey paste.  As you played the tape over
the heads, the oxide would start to scrape off, and pile up on the edges of
the heads or guide.  if the tape machine had a tape lifter to hold the tape
off the heads, it could literally scrape a layer of oxide off the tape. 
Then, when you stopped, the glob of oxide would be deposited on the tape
where you stopped, thus making that spot a real "klunk" spot.

It was someone at Ampex that came up with the solution, bake the tape.  The
initial device, was a cardboard box, that used 2 hair dryers on low, with
slots cut in the top of the box, and used a meat thermometer to monitor
temperature.  Keep it at 135 degrees for 8 hours per 1/4" reel in the
box. Separate multiple reels so air could circulate.  The idea was to drive
the moisture out of the tape.  It worked.  A new cottage industry sprang
up, baking tapes.

We bought a round Sunbeam convection oven, that also had "extension
rings" that allowed you to make it taller. We could handle 3 2inch
reels of multi-track tape at once.  We charged $25/hour for tape baking,
and saved many a project for people.  One of the later ones, was the Linda
Rondstadt Live orchestral project.  Dual 24 track recordings, 20 reels of
tape, took days to bake.  After baking, the tapes will keep their form for
many weeks.

About 4 years later, both AGFA and BASF suffered the same fate, and the
same corrective action was required.

There are thousands of tapes out there from that era that have to be baked
to extract their music.

There also is a generation of Ampex 456 that has a different problem.  In
the making of the tape, the "calander" the oxide side, to make it
smoother (shiny).  At one point, in the strive to increase the output of
the tape, they over calandered the tape, and on Studer, and some of the
Ampex ATR-100 machines, that tape would grind to a halt, not because of
sticky goo, but because of the too shiny.  Have you ever tried to slide 2
pieces of glass against each other?  That's what would happen.  The heads
on the tape machines got smoother and smoother, and the tape being so
smooth, would be like 2 pieces of glass.  Nothing more odd, than seeing a
$50,000 tape machine trying to move tape over the heads, pinch roller
engaged, and the tape is frozen in place.  The resolve for that one, was
ADD moisture to the tape.  We'd place a cloth that was damp, just touching
the tape as it entered the head block section, to "wick" the
tape.

Then there's the old acetate tape from the 50's and 60's. Those tapes will
curl away from the heads when you play them, as well as being super brittle
now.  I've taken many acetate tapes and had to splice them back together
when they've split/snapped during rewind. Or the splices have dried out,
and come apart as the tape is played.

Too much to remember...yikes....

--

Glenn M.
"Frank Haber"  wrote in message
news:459ff69e$1{at}w3.nls.net...
> (Gummy analog masters, baking)
>
> Ten years ago, 1973 Ampex 406 was the worst offender.  Has the rot now
> extended to 456, Agfa, BASF and Scotch?  I've never baked, or mothered, a
> 2" master.  Any different from 1/4", except for the time in the oven?

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