If you can't obtain the forementioned Marantz: There are two ways for
controlling tape speed on later open reel tape recorders. The first was
mechanical switching of belts or rollers; this kind is prone to speed
inaccuracy and definitely needs to have a fine tuning or pitch adjustment.
The second way was to electricall switch the motor speed in half: if the
original playback pitch is correct, the half speed will also correct in pitch.
Of course if you did your recording on the same machine, there would be no
pitch problem, regardless. Toward the end of the consumer open-real era, this
was most common method.
However, neither of these two will correct the pitch. The half speed playback
is down an octave for all the sounds. It takes digital processing to halve the
playback speed and maintain pitch. And, that's expensive. -ron