16 Jun
2015
16 Jun
'15
11:34 a.m.
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:
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.
Johnny
On 06/16/2015 11:08 AM, Henk Gooijen wrote:
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. 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"