I bought 604 around 1988/89. I love the ex amorphous head. 604 uses only one Small battery and last long. When the battery was low on cassette, I can still listen to radio for quite many hours.
I listen to it with a pair of Sony 484 headphone. The 484 has LC-ofc cable and diamond amorphous diaphragm.
The sound was so real, especially on hands crapping.( I use an Akai GX65 deck to make records with TDK SA chromium tapes from CD).
).
