On the Emulation of TU58s

Johnny Billquist bqt at update.uu.se
Tue Jun 16 16:17:37 CDT 2015

On 2015-06-16 21:20, tony duell wrote:
>>>> And yet another (possibly the most common one on computers) is to have a
>>>> small drive wheel that pulls the tape at constant speed across the
>>>> heads, and then have some other construction that drives the tape reels
>>>> depending on tape tension or length. Think vacuum columns or spring
>>>> loaded arms.
>>> That is closely related to the capstan and weakly-driven take up spool I think.
>> I would disagree. There is no slipping clutch. Instead, the motors (on
> True. I meant it was a system where the tape speed was determined by the
> capstan, and the reels are driven to keep the tape round up, not all over the
> machine room floor :-)

Ok. Then I would agree. :-)

>> The actual tape movement as such, is all done by the small wheel next to
>> the head, which just runs the tape past the head.
> Which is essentailly the same as the capstan in an audio tape recorder, albeit the computer
> drive doesn't have a pinch roller


>> I've been wondering if there is some sensor of tape tension/pressure at
>> the heads, and this will allow the drive to figure out how much
>> faster/slower the reels must run, relative to each other, in order to
>> keep the tape tensioned. Then you can figure out tape speed across the
>> heads (if you care) by just observing flux changes.
> Only if there is something on the tape. These computer tape drives could surely record on a
> totally blank tape and get the right number of bits per inch. So the thing can't use the data rate
> at the head as a speed measurement.

Ah... Good point. I didn't even think about writing. Stupid of me. :-)
Anyway, it seems the drive do some clever computations to figure out how 
to keep the speed constant.


Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: bqt at softjar.se             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol

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