On most Walkmans that have a recording function (Aiwas such as  JX/JS/JM, and Sony equivalents) a small permanent magnet is used as an erase head. These either swivel into place (logic controlled models or door mounted heads) or are pushed down (most later, cheaper machines, some larger sized ones). Only a few machines seem to use fixed powered heads (serious recorders like the D6C, some later machines).

Now obviously the latter is better. However, I am always curious about the permanent magnets, as in some models, they are mounted REALLY close to the running tape when not in use. (An example can be the JX505, and virtually most door mounted head machines.)

Is it possible that through many playback passes (like over a couple hundred), these permanent magnet erase heads that hover so close can alter the recording?

Personally I've seen no discernible ill effects, and obviously the machines are engineered properly to not cause this.)

Interesting thought to have never thought about

sony wm-f707

i think that it is the smallest player with AC erase heads. This model has dc-dc converter 1,2v -> 3,5v

Oh yes, the WM-F707. It says it uses proper electromagnetic erase heads rather than permanent magnet erase heads found on most Sony portable recorders.

it can either use 1.2 or 1.5V to 3.5V.

How about other walkmans? GX90, GX50 and other 90's walkmans? Do they also use AC erase heads?