[sci.electronics] Small DC motor speed control

keith@ux.acs.umn.edu (Keith MaloneyHuss) (03/01/90)

I use a small Sony microcassete recorder that has two tape speeds,
1.2 and 2.4 cm/sec.  As I use this only for voice recording, and 
"High fidelity" is not required, I was wondering if I could somehow
slow the tape speed to 0.6 cm/sec.  The recorder is powered by 3VDC
(two AA batteries).  Obviously, the electronics (amp, etc) need to 
keep getting 3V, but how is the motor speed reduced?  Is it a simple
voltage cut?  I don't care about wow and flutter as long as I can 
understand what is recorded.  Right now, at 1.2 cm/sec the sound
quality is excellent, and I'd like to be able double my recording
time if possible.
Any ideas on how to slow the tape speed to 0.6 (or 0.3?) cm/sec?

Thanks.
--keith