There isn't a specific standard for the number of guy anchors per foot of height. Generally, the number of guy anchors is a reflection of the site specific conditions and the engineer. The biggest factor would be the distance of the guy anchor from the tower. The more property that is available, the farther the guy anchor can be from the tower and the easier it is to design. Normally, the outer guy anchor is 80% of the tower height from the tower. However, on tight parcels, the guy anchors could be as close as 30% of the height. In the latter scencario, there may only be on set of guy anchors or 3 total anchors. In the former, there could be 3 or 6 total anchors.
All this being said, it would be typical for a 500' guy tower to have 6 anchors.
The photo below shows 4 anchors for one side of a tower- which means 12 total anchors.
This answer is courtesy of our own Molly!