This will be the last news until I put a link of a good quality video.
The machine now works. The way the take-up reel engages in playback/record mode is a bit tricky, but it works even if I need to try one or two times, so I'll leave it as is.
The sound quality is not bad at all, although quite limited in frequency. I think 2KHz shoud be a maximum as it's meant for voice recording. But the low frequencies are excellent. I tried to record myself but I was too close to the microphone so the sound was totally distorded.
The remote control works as well, so I'm quite happy with this recent purchase.
Hopefully one who speaks German will tell me what the woman says on the wire when the video is ready.