recovering cartridge tapes

Dave McGuire mcguire at
Mon Jul 19 19:33:21 CDT 2010

On 7/19/10 7:59 PM, Brent Hilpert wrote:
>>   Every vacuum-column drive I've seen has used pressure sensors to
>> determine the position of the tape loops within the columns.  Granted
>> I've not seen a HUGE variety of different drives, but...just sayin'.
> On the desk beside me, I'm looking at a part from a Honeywell vac-col
> tape drive. It's an aluminum extrusion 1/2-inch wide and about 6 inches
> long, with a masked glass plate on one side. Inside, spread along the
> length are 8 selenium photocell strips.

  Wow, that's nifty.  What vintage is that drive, any idea?

> I think this was located somewhere around the mid-point on the vacuum
> column, that is, the target area in the column to keep the tape loop at.
> Perhaps optical was chosen for servo response time compared to
> mechanical pressure switches.
> I haven't examined a large variety of drives either, but at least on
> some drives, the sensors are not distributed evenly along the length of
> the column, but are concentrated around the target area, and become
> sparser towards the extremities. Never seen it, but one could imagine a
> hybrid design with optical sense around the target area and pressure
> sense further out.

  Yes, I've seen those nonlinear sensor distributions too.  My Kennedy
9400 uses continuously-variable pressure transducers along the vacuumn
columns.  They are effectively variable capacitors.

  That drive also has an 8088 CPU and an 8279 keypad/display interface
in it.  Neat stuff. :)


Dave McGuire
Port Charlotte, FL

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