[78-L] half track tapes

[Michael Biel]

At 09:41 AM 8/8/2009, you wrote:
> > Remember the Wollensak with its dial for shifting the playback
> > head down a millimetre or two to play half-track tapes with
> > equal balance? Any other machines have a feature like that?

From: "Robert M. Bratcher Jr." <bratcher at pdq.net>
> Which model is that? 

Wollensak T-1515-4, T-1616, T-1580 (I think that's the number), and
several Revere's -- the stereo playback versions of the single knob and
the pushbutton models if they have a suffix "-4".  All of their stereo
playback machines from 1959 onwards were this way until they started
making machines that recorded in stereo, and they also sold an adapter
head-set.  The major purpose of the "Head Track Selector" was to enable
the recording on the lower tracks on these machines which only recorded
in mono.  This gave you four mono tracks, but they played back in
stereo.  Since the 2-track tapes were so common back then, the extra
notch to lower the head just slightly was quite handy.  The BEST thing
these things could do was search out the best part of the tape for
warped full track tapes.  It is still a very valuable technique to play
back old full track tapes.  (The second best technique archives use is
to have a quad-four head and pick out the ONE track which is the best.) 


There may have been a mistake in an earlier posting about which track
was weakened when playing a half-track stereo tape on a quarter-track
machine.  It is the RIGHT channel which is weakened.  The Guard-Band
space in-between the tracks is wider for stereo then it is for mono half
track.  The lower track of the 4-track system will hit half on the
guard-band and half on the lower track of the 2-track stereo tape, so it
needs to be slightly lowered.  This also has the benefit of moving the
upper track away from the edge of the tape which is where physical
damage can first happen.  It also helps when recording a tape to be
played on the full track Ampex portables 600, 601, and maybe the 602. 
These machines had a slightly curved play head which avoided the upper
and lower edges.  They completely miss the upper quarter-track.  The
record head is flat and records the full width of the tape, but since
portables might be working with damaged tape, this helped make the
playback of full track tapes more consistant.  There might have been
head-bump compensation.   

>I had a worn out Webcore Music Man that would shift the playback
> head with a lever on the back of the head assembly. Threw it
> away when it stopped playing tapes at 3.75 ips & was having
> trouble with 7.5 ips. Belts were shot really bad but then 
> I got it for free.....
 
The Wollensak/Revere device moved BOTH the Record/Play and the Erase
heads.

> Today, of course, you just look for a Technics 1500 with the quarter-
> and half-track playback heads. Still quite a few of them out there. dl
 
 Yes for 1.5k to 1.7k on the bay site. 
 
The Otari 5050 machines had an extra quarter track play head in the
second of the 4 head blocks.  It was standard equipment until the Mark
IV, when it became an option WHICH NOBODY TOLD ME WHEN I BOUGHT MARK IVs
FOR MY SCHOOL.  So those last 4 machines have only three heads and
screwed me up for playing my home recorded tapes.  I had to use the
earlier ones we had there.  By the way, the record and play heads are
exactly the right spacing for Staggered-Stereo playback!!  Set one track
on play and the other on Sel-Rep and it will play them!!

Mike Biel  mbiel at mbiel.com