On the Emulation of TU58s

Johnny Billquist bqt at update.uu.se
Tue Jun 16 13:34:14 CDT 2015

On 2015-06-16 20:30, Henk Gooijen wrote:
> -----Oorspronkelijk bericht----- From: Johnny Billquist Sent: Tuesday,
> June 16, 2015 8:22 PM To: cctalk at classiccmp.org Subject: Re: On the
> Emulation of TU58s
> On 2015-06-16 20:20, Chuck Guzis wrote:
>> On 06/16/2015 11:08 AM, Henk Gooijen wrote:
>>> The round (approx 2" diameter) "bearings" of the TU80 do not rotate.
>>> Instead, the metal has tiny holes. Air pressure pushes the tape away
>>> from the bearings. As the tape moves, due to movement pressure, the
>>> tape comes closer to the air bearing. That is measured. To get the
>>> air pressure back to some sort of equilibrium the pickup or supply
>>> reel speed is adjusted.
>>> That is how I understand the mechanism ... now writing this down, I
>>> think I should read up the Theory of Operation chapter ...
>> Pretty much the standard CDC vacuum-column design since the 1960s.  The
>> TU80 is, after all, a CDC product.  Two counter-rotating capstans--tape
>> movement is determined by applying positive or negative pressure to
>> ether or both (i.e. positive pressure on both results in the tape
>> "floating"
> Uh... The TU80/TU81 do not have vacuum columns...
> Johnny
> -----
> well, the tiny space between the tape and the air bearing could
> be regarded a vacuum column, but it's a very short one :-)
> The two air bearings are immediately above and below the R/W
> and erase head. And they do *not* rotate. The tape glides on
> an air cushion over the bearing.

Hmm, I guess it could. But it is a very different construct compared to 
a vacuum column drive. In this case we're talking about overpressure to 
act as a cushion, and not underpressure to act as a takeup/buffer mechanism.


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