[Coco] Importing CCRs

[Gene Heskett]

On Sunday 01 April 2007, Kevin Diggs wrote:
>Gene Heskett wrote:
>> Yes, the original kraft paper was replaced by a plastic film, and the
>> coatings also improved with better binders & other metals alloyed into
>> the rouge, finally getting so smooth that head wear was much less of a
>> problem.  Now, its only really abrasive in high humidity conditions.
>> Keep it at less than 20% RH, and the wear is almost a non-factor.
>
>Well there is another fun fact! I did not know that humidity had any
>effect on head wear. I assume you are primarily talking about those
>machines that use some kind of drum? According to the humidity meter it
>is 48% in my house. What kind of wear am I going to see?
>
Somewhat below average.  Its when the tape is stored in a normal room, and 
has had time to acclimate to a 90% humidity day that it turns into a 
strip of 1200 grit.

>> In the '70's when I worked for NETV, at one location out in Nebraska
>> there was 3 of those 2" wide quadruplex machines in their own air
>> conditioned, dehumidified room, being used for the one hour time delay
>> by the NETV commission network since NE has 2 time zones.  A roll of
>> tape went on those machines and didn't come back off for months, just
>> recorded, rewound and played, rewound and re-recorded, wash, rinse,
>> repeat, 19/7/365. They knew the head life they were getting was good
>> but it was really driven home when they had a rotary transformer in
>> one of them fail, and it was only a cheap 100 hour rated head. 
>> Checking the books, that head then had 7800 hours on it.  The head
>> re-builder fixed the transformer for nothing, said the tips were fine
>> & sent it back.  It ran to something over the 11 thousand hour mark,
>> but that was typical.  No food, smoking or anything else was allowed
>> in that room.  11,000 hours from a 100 hour pro-rated head is pretty
>> good IMO.  At most stations, the budgeted cost for operating expense
>> on those was $20/hour, 15 of it due to head wear.  The other 5 was how
>> much more a tech that understood them cost to keep on the payroll...
>
>Uhm. A what? What is a quadruplex machine? Was the humidity connection
>not well known?

A quadruplex machine is one of those old broadcast vcr's that used 2" wide 
tape, and the head had 4 tips arranged at 90 segments on the rim of the 
wheel, spinning at 14,400 rpm, so the effect was that of laying a new 
track across the width of the tape as each tip crossed the tape as the 
tape was pulled past the head at 7.5 ips in the later machines, 15 ips in 
the first ones.  Because of the orientation of the magnetic fields, the 
control and audio tracks were laid over that longitudinally, and the 
cross-talk was minimal, somewhat like using polarized light.  The word 
quad meant the number of heads and the crossed magnetic fields were part 
of the multiplexing, hence I believe, the quadruplex moniker.

And yes, the humidity connection was fairly well characterized by about 
1970-ish when this took place.  The room was constructed with that in 
mind, had precipitron air cleaners in the air conditioning to keep the 
particulates down too.  On average of those 3 Ampex VR-1200's, the 
shortest wheel life was on the machine directly under the precipitrons 
exhaust, the other 2 were in relatively quieter air.  Under those 
conditions, it was still getting 6000+ hours out of a 100 hour prorated
head, the other two averaged 2-4 thousand more.

Keeping it that clean while effectively being in the same building with a 
tv transmitter that pulls a couple of cubic miles of dirty air (this is 
in the middle of a cornfield being plowed, planted, cultivated and 
harvested) in just for cooling each day was I think, about as close to 
building a spaceship in Nebraska as you could imagine, but it worked.  
They were very carefull to maintain a positive pressure in the room so 
that when the door was opened for human access, only the dirt carried in 
on the person was a factor.

As they were remote controlled through glass windows, humans didn't have 
to enter very often.  Usually only to replace the tape end on the spool 
if somebody wasn't watching the rewind carefully enough.  As the end of 
the tape was usually wrinkled up some, pulling it past the head was 
considered a no-no.  With accurate control track counters, they could be 
rewound to within 10 frames of the start of the old recording if paying 
sufficient attention, which prevented the tape from becoming disconnected 
from the reel hub.  ISTR they also had some magic marker stuff painted on 
the back of the tape about 10 feet from the ends.  Which system they used 
was probably up to the individual operator.  And he didn't have a lot of 
time to do this if the third machine was down as the on the hour break 
was only 1:30 and the rewind time was over a minute for an hour's tape.

They were pretty good machines in their day, but gawdawfull expen$ive to 
operate.  In addition to the limited wheel life, tape was several hundred 
a spool, and some were _real_ power hogs.  The Ampex AVR-2 needed nearly 
25 kw in electrical service, and about that much more in air conditioning 
capacity.  The much more utilitarian VR-1200 still used about 15kw by the 
time you counted the air compressor and air conditioning load.

>kevin

-- 
Cheers, Gene
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