I finally got the cables for my dad's amplifier and it seems to work well, except that I can only hear one channel when I plug in my headphones.
EDIT: I've tested a bit and it seems the signal simply doesn't reach the left side of the amplifier. The actual connections are good and if I plug a couple of headphones that cause interference, the left needle moves like the right one.
The left needle doesn't move when I first power up the amp so this must be a very easy fix. I opened the case and everything seems to be in top shape, it must be a bad conneciton or something like that.
Thoughts?