On 11 Jan 2005 05:38:16 -0800, wrote:

generally yes, most dc motors used in cassette decks have a speed pot
which you could tap into.
-Ben

Correct. There were even tape machines made with pitch and speed
control for specialized use.
On the consumer end there were cassette recorders that had speed
sliders for the purpose of speeding up dictation time.(Try Radio
Shack, my wife has one packed away somewhere she used to use for
interviews that she purchased there.)
On the commercial level we used tape machines with sliders for pitch
and speed in the post editing phase of film production.(Ever wonder
how the background music got those eerie variations in speed and pitch
in those old horror films?)
Seems I remember someone made a line of tape recorders around the mid
70's that had speed control with pitch correction as well. Allowing
one to speed up the recording without having the pitch/tone go all
squeeky.