Re: [ARSCLIST] Ampex 456

[Steve Puntolillo <steve@xxxxxxxxxxxxx>]

Hi --

Looks like I've been invoked.

OK, so Robert Hodge wrote:

> >>> I suspect that due to the increased surface area of your tape, you
> >>> would have to increase the baking time normally used for 
> 1/4 inch tape.
> >>>
> >>> Library Of Congress recommends 8 hours at 130 degrees for 
> pre 1975 and
> >>> 5 hours at 130 degrees for post 1975 and later for 1/4 inch tape.
> >>> I've never baked 2 inch , but this is the path I'd follow unless
> >>> someone has done it differently with success.
> >>> 64 hours at 130 pre 1975 and 40 hours 130 for 1975 and later.
> >>> ( Seems like a lot. ) But the math indicates it so. And the same
> >>> amount of time for cooldown which is equally important..

Tom Fine replied:

> >> Bill Lund, formerly of 3M, and a tape chemistry expert, 
> suggests 12 hours bake, 12 hours cool to 
> >> room temp before playing. I trust Bill and have used that 
> method successfully numerous times. 
> >> Earlier experiments with shorter times were not residue 
> free but did result in playability.
> >>
> >> No offense to the LOC, but Bill actually worked at 3M and 
> was involved with figuring out what was 
> >> wrong with Scotch 226.

Steve Smolian contributed:

> > It depends on the width and thickness of the tape.

And Tom Fine countered:

> I'm not so sure about this. Ask Steve Puntollilo, who has 
> successfully baked and transferred many 
> sticky 2" tapes. As I understand it, 12 hours at the right 
> temp will do it for any tape.

Ouch. Well not *any* tape. In all fairness to Tom and for the sake of
this group discussion, perhaps I should provide a bit more detail.

I've often wondered how to determine mathematically the right "formula"
to get the innermost 1/4" of tape in a 2" reel to bake for 12 hours at
130 F. And, if (and this is a "big if") we're indeed attempting to
evaporate moisture out of the tape, I've also wondered what effect the
thickness of the tape has on the path of escape for the moisture. 

(Note that I've checked and confirmed that an untreated 2" SSS tape will
leave oxide on static surfaces in the tape path *uniformly* top to
bottom. I think it's interesting that the condition is not perceptibly
worse nearer the tape edges. In fact, not only is that the case, but
I've also found that the deeper into the reel one goes, the worse the
condition seems to get. Tapes that are trying to play near the outside
layers will often crawl to a stop as we get deeper into the reel. This
is the opposite of what I would expect to see happen.)

If we use the LOC formulas as a benchmark, it certainly seems impossible
that it could take 8 hours to effectively treat a pre-1975 1/4" tape but
only 12 hours to effectively treat a 2" tape.

As Tom indicated, we have incubated a lot of tapes here. We do this
using a Fisher Scientific laboratory incubator.
http://www.sonicraft.com/a2dx/a2dx_tech.html 

While I did tell Tom we incubate tapes for 12 hours, it's important to
note that I don't start counting the 12 hours until the incubator
reaches 130 F. I also leave them in the closed incubator for at least 12
hours from the time the incubation cycle ends. This allows them to cool
to room temperature more gradually. Also, we will not play a tape until
at least 24 hours from the end of the incubation cycle.

There are a few points I may not have mentioned to Tom yet:

(1) Sometimes a tape won't make it all the way to playability on the
first try. Ironically, these tapes are more often 1/4" tapes than 1/2",
1" or 2". Don't ask me why this is. In fact, I respectfully take issue
with the LOC about the 5 and 8-hour incubation period for 1/4" tapes.
Maybe these times were arrived at a long time ago? I have reason to
believe that a longer incubation period is necessary today over that of
a decade ago.

(2) Sometimes I set the incubation period for a little longer than 12
hours. I might do this because the incubator is very full. Or it may be
because I've analyzed a given reel or batch of reels and found that they
have a worse than average case of SSS. Or both.

The amazing thing is that it *doesn't* take 40-60 hours to treat a 2"
tape (or batch of 2" tapes). If it's one 2" tape with an average case of
SSS, after 12 hours of incubation, 12 hours of slow cooling in the
incubator and 12 hours of standing at room temperature, the problem
should have yielded and the tape should be playable.

I honestly can't explain this. I only know that the process works. More
often than not, even the ugliest looking 2" tape(s) will play
beautifully.

I hasten to say that I have no desire to shortcut the process. In fact,
the opposite is more the case. I usually overestimate the time it will
take the incubator to reach full temperature, resulting in actual
incubation times that are somewhat longer than the time I actually think
will be necessary.

Hope this info helps.

Best,

-- Steve 

===================================================
Steve Puntolillo
Sonicraft Inc. - Analog and Digital Audio Services
http://www.sonicraft.com
===================================================