27 Jan
2015
27 Jan
'15
6:27 p.m.
On Jan 27, 2015, at 17:22 , Brent Hilpert <hilpert
at cs.ubc.ca> wrote:
On 2015-Jan-27, at 2:36 PM, Mark J. Blair wrote:
>
> I found a specification that includes the magnetic track dimensions of the DECTAPE II
on Al's site:
>
>
http://bitsavers.trailing-edge.com/pdf/dec/dectape/tu58/TU58_Engineering_Sp…
[...]
Both the
DECTAPE II media and standard audio cassette media are 0.15" (3.81mm) wide. DECTAPE
II has two .057" (1.448mm) wide tracks, centered 0.046" (1.168mm) apart.
Something's funny there, the C-to-C distance between two tracks has to be greater
than (with separation gap as shown in the manual) or equal to the track width, that is:
C-to-C = TW/2 + SEPGAP + TW/2
C-to-C >= 2*(TW/2)
but:
.046 < .057 Do some auto-reversing stereo decks have 4-transducer
heads? The ones I've seen (not many, so I don't know) mechanically flip a
2-transducer head around 180 degrees.
I have never seen one that moved the heads. I'm pretty sure that I've seen ones
that simply have four coils/gaps, just like the head in a 4-track audio recorder would
have.
I think the question would be what are the head-gap
widths. It's got to be small enough to adequately discern the linear-rate-of-change of
the flux variation on tape. I don't think that's necessarily going to correspond
to the AC bias F in audio recording, but yes, it's still in the ballpark of 20KHz
hi-fi audio.
I'm also blindly assuming that the coil/gap orientations are the same. Well, I could
always avoid the problem by using a real TU58 head; then I have to guide the tape
externally to the head (perhaps using tape guide spools harvested from a sacrificial tape
cart) instead of using the sheet metal guide notch found on typical audio tape heads, and
I need to get that epoxied-in head out of the transport and provide some means to mount
and adjust it. In contrast, my recollection of audio tape heads that I've seen is that
they're usually screwed in place (not epoxied), and in better drives there's even
an alignment adjustment.
--
Mark J. Blair, NF6X <nf6x at nf6x.net>
http://www.nf6x.net/