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Re: Antwort: Re: [AV Media Matters] Convection Oven
At 09:35 12/05/00 -0700, Catherine wrote:
>What are the recommended temperatures and "baking time" for
>tapes? I have heard that a longer baking time (100 - 120 hours)
>at lower temperatures of 50=B0C is preferable to a shorter baking
>time of 9 hours at the higher temperature of 70=B0C. Within what
>time span do the tapes start disintergrating again after baking?
>Does a longer baking time help prolong this interval?
At the risk of a drubbing from the longer-term members of the group, I am
copying an exchange from last December, when this subject was discussed.
>I've got a circa 1982 Ampex 2" 16-track tape that I want to transfer to
>ProTools. It has been stored in various conditions and levels of
>humidity since that time, but has not been played since then. I've been
>told that I'll need to "bake" the tape to keep the acetate from
>on the heads. Is this normal (and is it the only way to do it right?)
This is a well-known problem which affects tape (not only Ampex) of this
vintage. It is to do with the binder chemistry being changed around that
time for something which (over a period of time) becomes 'sticky'. It's
commonly known as 'sticky shed syndrome' and it's not the acetate which
comes off, but the iron oxide!! If I recall, Graham Newton has some
information on his website about this subject
(http://www.audiorestoration.com) which you might like to have a look at.
Baking the tape is the accepted solution for the problem, although it does
*not* effect a permanent cure. Something like 6-8 hours at 130-140
Farenheit is the usual sort of figure recommended. I have baked
(must be well in excess of 100 by now) and have not had a failure so far.
All my tapes have been 1/4" masters, but I don't see that a 2"
would be any
different. It does no harm to leave the tape for longer, but I would be
very wary of going over-temperature.
You can be fancy about it and use a temperature controlled, electric oven
(not a gas one). Personally, I do mine in a cardboard box, about 2 ft
cube, with the tapes supported on a wooden dish rack, two electric light
bulbs, a dimmer unit and a photographic thermometer :-)
After baking, spool the tape a couple of times before playing.
>This person said that after baking, the tape would only be good for about
>2 to 4 plays, so I want to make sure.
I don't think it is a case of the number of plays, so much as the time it
will take for the binder to re-absorb moisture from the atmosphere (which
is what causes the problem in the first place). After baking, I place the
reels inside a sealed polythene bag (assuming I am not going to use them
immediately). They have certainly been playable after a month
To answer your specific question a longer time seems to do no harm, but it
will not extend the interval - once you have removed the moisture, that's
as far as you can go and it's more a case of how long it takes to reabsorb
moisture from the atmosphere. Put another way, how long the tapes will
remain playable depends on the storage conditions after baking. I easily
achieve 4-6 weeks, using a sealed bag and keeping the tape in a (coolish,
for Spain) room at some 20 odd degrees C.
They may well last longer, but I have never had the opportunity or need to
test this out.
Upon re-reading my original post, I should have made it plain
that the tape
should be allowed to cool naturally to room temperature before spooling or
playing (I always leave them for 24 hours after baking).
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