The cheap Japanese toy tape recorders available in the 1960's did *not* use capstan drive. Instead, the bases of the feed and take-up reels had a rubber ring on the outside. A motor contacted that ring to drive the play, record, rewind, and fast forward functions. Thus the speed of the tape across the head varied depending on the position in the tape and the slackness in the tape winding.
I am told that these recorders used a 10,000 Hz bias signal to record the audio on the tape. I want to design a device with a second head before the play head, that detects the 10,000 Hz signal bias on the tape and adjusts the tape speed so that the audio plays at the right speed as it passes the read head.
I realize that the quality of the recording playback will vary according to how much the original tape speed was at record time. But such a device would allow me to re-record old tapes in a consistent way.
Any ideas???