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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
coming off
>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
many tapes
(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
when treated
this way.

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).

Graeme Jaye

Personal-CD - Affordable Audio Restoration


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