Measuring on walkman's head.

I have measured the inductivity of reproducing heads. It was about 80 mH.
Each of the 3 heads in the picture is a four tracks head (two in one direction for stereo tape reproduction).

On the left picture (1.head) we see, that the coils from the head are serialised to play both channels at once. The electronic part of this cheap walkman is equipped for two channels, but only one of them was used. At the output the channels of the connector for headphones are also short-cutted with a piece of wire.

One channel has a 3 stages transistor amplifier with Si-transistors - two 9014(low noise) and 9013. For me it was interesting to measure the signal comming directly from the head. I couldn't catch it very exactly, because the signal was very weak. The AC voltage could be some tenths of µV with current about hundreds of nA.

Therefore the wires comming from the head are shielded. The inductive resistance on the audio frequencies is in the range of kiloohms. In the electronic part of the other two devices there was already used an IC (e.g. AN7108).

We can also see a comparison between a mechanics of a very simple player with play and fast forward functions

and another walkman with play, fast forward, fast backward and recording features.