Hello Tomas,
It is probably not likely you are going to find easily find original B & O replacement belts in good condition for the 1700/1600 receiver. After a long time of searching I did find a source for making my own replacement belts. The belt is not the exact width and needs to be trimmed down and spliced to make it a loop. But if done carefully looks better than the original and is much more durable. I would rather have the originals but that is an unlikely option.
There are different places on the internet you can find them. If you do a search for “Industrial Drive Timing Belts HTD 3M Pitch Timing Belt Width 30mm Open-Ended Transmission Synchronous Belts” you will find several sources, it is branded 3M but made most likely in China. It is available in different lengths and I would get more than you think you need. You will have to cut the 30mm to around 27-28mm width and cut the length based on an old 1600 belt. Getting a clean cut between the belt ribs for a good splice is the tricky part. That is why I would get more than I need. If done cleanly and straight you then use Gorilla Super Glue Gel and clamp it for 24 hours. I have done two belts and the seam is invisible. You can use WD-40 and a cotton swab to remove small amounts of the visible glue.
John
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