In 1951 and 1952 I built my first audio tape recorder and it indeed had
a three-head assembly that rotated contrary to the direction of the tape
travel.

I invented and designed and built this machine without having seen the
innards of another tape machine or knowing the technique being used by
any of the companies then making tape decks or recorders.

I went to Charlotte, MI where the Recordio Company was making tape
recorders for RCA and others.  It was there that I was able to obtain
certain parts that I needed through their salvage department.  I
obtained several heads and motors and other parts that I used in the
design and construction of my own machine.

I used a system of slips to carry the lines for the heads as they
rotated around a shaft and the assembly in turn was driven by a variable
disc drive so that it would control both the head rotation speed as well
as the tape transport speed so that the heads and the tape remained in a
constant relationship so as not to vary the pitch although allowing a
wide variation in the speed of the recording or playback.

It was necessary to make the tape guides adjustable so that I could
assure that the tape path was far enough around the head rotor to make
sure that one of the rotating heads was in contact with the tape at all
times but not two at the same time.  Thus, it was possible to keep the
head to tape speed ratio the same at all times but speeding up the
rotation of the heads and the speed of the tape transport thereby
producing the same pitch as was originally recorded but shortening or
lengthening the time which resulted in the ability to speed up or slow
down the playback at the originally recorded pitch.

In fact, it was this very same tape machine that I built, that I also
used in my original experiments with binaural Amplitude Modulation
radio transmissions and receptions that I conducted in the early fifties
and which were later written up in Radio World, a broadcast radio trade
publication, in which it was established that I was the originator of
what is now called "Stereo AM" but which I called "bi-naural amplitude
modulated radio transmissions."

This was one of my 'brilliant' ideas that I've had over the years.
Mr. Stuart Rockefeller, of the Robotron Corporation, also a radio ham,
W8NJH, backed me up in my experiments and even took me to Kalamazoo to
see his patent attorney.  Stu had patents numbering in the dozens,
many having to do with electronic welding controls, and was very kind
in urging me on in my own endeavors.

Unfortunately, some of the circuitry that I'd incorporated into my
"Stereo AM" were similar to circuits that had been earlier patented by
the Hazeltine Corporation, and Mr. Woodhams(?) advised me against trying
to deal further with that company.  It just so happens that between the
Hazeltine Corporation and the Radio Corporation of America, they had
patents on nearly all conceivable tube circuitry at that time.

In 1956, after I bought a house in Onondaga, MI, I took that home-made
tape machine to Charlotte, MI, now only about twenty miles distant, and
showed it to the engineers at Recordio and let them have a look at it.
Several of them said it couldn't be done but they played with it for a
couple of hours one day and finally came to the conclusion that it _had
been_ done.

Unfortunately for Recordio, they were having financial problems and were
on the route to being no longer in the tape recorder business.  As a
result, nothing further was done with my design, except that one of the
people that I had shown it to earlier, wrote an article about a similar
machine that he had built patterned after mine.

Anyway, recording devices have an interesting history, much of which
is either today unknown, or ignored.  I had a friend in 1944 who was
also a member of the CAP Cadets at Willow Run, MI.  He lived in the down
river Detroit area and he had managed to build a machine that could
record several minutes of television.  I never was able to get to his
house to see it for myself but I talked with some other people who did
witness its performance and assured me that it did as he claimed.  At
that time TV wasn't a big deal for most people so I guess he didn't
pursue it further.  I lost track of him when I left Ypsilanti and moved
to Chicago.

That's where I was fortunate enough to meet a fellow, Ralph Glade,
who encouraged me to build by first oscilloscope.  That was in 1945.
I didn't do much of anything until after I got out of the Army in 6th
June 1949 and returned to Ypsilanti.

Hal Davis