I've baked literally hundreds of 2" audio tapes including several 
seasons of TV episodics. Virtually every width, thickness and format of 
polyester base audio tape ever made. My experiences roughly parallel 
that of John Chester's comments. I say "roughly" because I tend to bake 
audio tapes at a lower temperature which extends baking times somewhat. 
The determining factor for audio tape baking time is the condition of 
the tape itself. I've had 1/4" tapes need a longer time in the oven that 
the average 2" tape.

Azimuth for 2" multitrack tapes:
2" multitrack tape decks were not routinely adjusted for azimuth. Ampex 
1" and 2" tape decks, for example, were fixed azimuth "What you bought 
is what you got". Adjusting azimuth on a multi-track tape deck is not an 
exercise for the faint-of-heart. One cannot assume that the outside 
tracks are the ones to use for adjusting azimuth. Due to small 
differences in manufacturing tolerances, the pole pieces are not always 
in perfect alignment so the tech has to determine which two pole pieces 
(tracks) represent the best average for that particular head stack, an 
adjustment that will differ from head stack to head stack. Record 
projects were often started at one studio and then moved to different 
studios for overdubs and mixing. The azimuth of the multi-track machine 
at a given studio was never (in my experience) a consideration. Mixing 
was a different story. As the engineer on a given project, I always 
tried to mix at only one facility (whichever was the favorite of the 
producer) for all of the obvious reasons.

Corey
Corey Bailey Audio Engineering
www.baileyzone.net


On 4/7/2015 4:34 PM, John Chester wrote:
> On 4/7/15 5:26 PM, Richard L. Hess wrote:
>> On 2015-04-07 3:18 PM, Eric Jacobs wrote:
>>> 2-inch tapes with sticky shed may not respond as well to baking as
>>> 1/4-inch.
>> That is true in the sense of in the same or similar time frame.
>>
>> I don't think there are precise formulae for predicting the time 
>> either to achieve thermal equilibrium or to achieve moisture 
>> equilibrium in a tape pack. Vos (1994) inspired me to develop a rule 
>> of thumb that moisture equilibrium appears to take 1500 times as long 
>> as thermal equilibrium in a one-inch tape, based on my extrapolations 
>> from his curves.
>>
>> We have long suspected that the width of the tape was a large 
>> modifier of this ratio. I based my estaimate on Vos's graphs which 
>> seemed to indicate that a 1-inch tape pack, might achieve thermal 
>> equilibrium might in 100-200 minutes while it might take 100-200 DAYS 
>> to achieve moisture equilibrium. I felt that a factor of 1440 implied 
>> far too much precision in the calculation, so I rounded it to 1500.
> 100 days to achieve moisture equilibrium?  That must not be required 
> for curing sticky-shed audio tapes, because they don't need to be 
> baked anywhere near that long.  I recently asked Steve Puntolillo (who 
> regularly bakes 2" audio tape) how long he baked it.  He said he gets 
> clean playback on most 2" sticky-shed tapes after baking for 2 days, 
> and cooling and resting for 1 day.  My recent experience with 1/4" 
> Ampex 407 is that one day bake and one day cool and rest is almost 
> always adequate.  However, both Steve and I have observed that the 
> required bake time has about doubled compared to a few years ago.
>
> -- John Chester
>