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Hi, Tom,

Your wondering is along good lines. I examined some Sony PR-150 with 
Graham Newton's stereo microscope which he uses for examining disk 
grooves. He had a selection of dental tools there  so I started probing 
around and the mag coat was soft and could easily be ploughed with the 
dental tools...ploughed rather than just scratched. The mag coat when 
ploughed had residual that was lumpy on either side.

This was years ago and when I read about Glass Transition Temperature 
(Tg) the Bhushan Tribology book, I somehow connected the two which was 
when I started playing around with cold playback. Later, Dr. Ric 
Bradshaw while he was still at IBM measured some tape (I forget if it 
was PR-150 or 3M-175) to have a Tg of about 8 °C, or 46 °F. Measuring Tg 
is somewhat subjective and involves plotting a curve and then estimating 
the breakpoint in the curve.

A confirmation came in a round-about way from work done at Indiana 
University. They were able to play a squealing tape, but not 
immediately, the tapes and machines sat in a walk-in cooler set to 4 °C 
over a weekend and it worked then.

What is complex is that cold playback works best for tapes that squeal 
(have rubbery mag coats) but are not visibly shedding.

I have had most success with cold playback on cassette tapes as the 
fridge I bought for cold playback can't keep up with the heat output of 
a pro tape machine. I was unsuccessful in using Studer A810 machines in 
the fridge (and now no longer have any). The APR-5000 is a bit too large 
to fit in and I think it throws off more heat than the A810.

Christopher Campbell had success with using a Sony APR-5000 outside his 
office in the autumn at similar temperatures a few years ago and was 
able to transfer all the squealing tapes in his collection. His 
experience, however, passes on a caution. When he first tried it, his 
ReVox C270 died. I think the capstan motor seized (like my A810) but 
somehow this also took out the capstan servo, at least this is what I 
think happened.

Finally, high(er)-speed playback can also help. Jay McKnight originally 
suggested it and David Crosthwait and I just went down the "air bearing" 
rabbit hole in a few messages in this thread. Shai's confirmation is 
good. I have found the Racal Store 4DS Instrumentation (IRIG) recorder 
with four-track inline heads to be a good machine for this with the 
caveat that some post-transfer EQ is probably necessary. The profiles of 
the heads are sharper than in an audio machine which may be due to the 
poorer spec of required low frequency performance. (The philosophy for 
the IRIG instrumentation standards seem to say "you have the option of 
FM recording available, use it instead of fussing with head bumps and 
fringing.")

Cheers,

Richard



On 1/25/2016 7:45 AM, Tom Fine wrote:
> I'm wondering if this is an extreme case of what I've  been theorizing
> about the surface getting degraded from going sticky and then being
> baked. Maybe the Sony and 3M tape that Richard has to cold-play have a
> surface so screwed up, either because it goes very un-smooth or
> something happens where binder material "dries out" so it doesn't shed
> but remains somewhat "rubbery" right at the surface have a chemistry
> that makes hydrolysis particularly damaging to the physics of the material?
>
> -- Tom Fine
>
> ----- Original Message ----- From: "Shai Drori" <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: Monday, January 25, 2016 1:03 AM
> Subject: Re: [ARSCLIST] One more sticky-shed data point - Richardson
> treated tape
>
>
>> High Richard
>> I think we had a discussion about these two in the past. The PR-150 has
>> some batches that run fine but most do squeal. I haven't even tried
>> baking
>> them except once just for the hell of it and of course no luck. Double
>> speed playback works when possible but I haven't had any lately so
>> haven't
>> tried cold play yet.
>>
>> Cheers
>> Shai Drori
>> Expert digitization services for Audio Video
>> Hi Res scanning for film 8mm-35mm
>> www.audiovideofilm.com
>> [log in to unmask]
>>
>> On Mon, Jan 25, 2016 at 6:10 AM, Richard L. Hess
>> <[log in to unmask]>
>> wrote:
>>
>>> Hi, John,
>>>
>>> This is indeed true. HOWEVER, my success rate for baking tapes that are
>>> suffering from squealing and/or deposition that are not back coated
>>> is much
>>> lower.
>>>
>>> This raises another question. If all binder breakdown is hydrolysis,
>>> then
>>> why doesn't baking cure it 100%? I'm thinking of Sony PR-150 and 3M-175.
>>>
>>> These two seem to show the falling Tg, but don't have the shedding. They
>>> are outliers and inconsistent.
>>>
>>> Cheers,
>>>
>>> Richard
>>>
>>>
>>>
>>> On 1/24/2016 3:41 PM, John Schroth wrote:
>>>
>>>> Back-coating may instigate or speed up the hydrolysis process but I
>>>> cannot ignore the fact that there are still obscure instances where the
>>>> tape had no back-coating and suffered from SS. Richard, you have noted
>>>> this in the past and I have had this happen in at least two instances
>>>> that I can recall. I'm at home today so I don't have access to my
>>>> notes,
>>>> but it was clearly sticky shed on tapes that had no back-coating. So
>>>> one
>>>> should not "always" equate back-coating with sticky shed.
>>>>
>>>> Just my two cents...
>>>>
>>>> John Schroth
>>>> MTS
>>>>
>>>>
>>> --
>>> Richard L. Hess                   email: [log in to unmask]
>>> Aurora, Ontario, Canada                             647 479 2800
>>> http://www.richardhess.com/tape/contact.htm
>>> Quality tape transfers -- even from hard-to-play tapes.
>>>
>>
>>
>
-- 
Richard L. Hess                   email: [log in to unmask]
Aurora, Ontario, Canada                             647 479 2800
http://www.richardhess.com/tape/contact.htm
Quality tape transfers -- even from hard-to-play tapes.