On the Emulation of TU58s

[tony duell]

[Driving tape]

> Another solution is to avoid the problem entirely by not requiring constant linear speed.  That’s what DECtape 
> (the real one) does.

Sure. A number of tape drives were built that way, the HP9865 (and thus the built-in tape drive on the
HP9830) is another example. 

>
> > One is to drive the tape itself using a capstan and maybe a pinch roller. Then have the takeup spool
> > driven too fast with a slipping clutch in-line. And a weak brake on the supply spool. This of course is what
> > was done in audio recorders (reel to reel and cassette), Video recorders (ditto), etc.
> 
> Or a variant: drive the takeup reel with a controlled torque motor and no slip clutch.  I think professional grade > tape decks may have been built that way.

They were. Or at least some semi-professional audio recorders were built like that. The Revox G36 (736) and Brennell Mk 5 among them (I happen to have both). Actually, the Philips V2000 video recorders (home machines,
not professional but quite the best of the home systems) did that. They had a pair of DC motors to directly
drive the 2 spools along with the capstan and head drum motors. No slipping clutches. Back tension was 
provided not by a light brake on the supply spool but by a suitable current through the supply spool motor
in those machines.

-tony