This is a rare M55rp model from the Regular Phase/Printed Ribbon line of Fostex microphones. It appears to be designed as a vocal microphone ala SM58 but sounds much better than an SM58 - on vocals, guitars and most other applicaitons.
The microphones from Fostex's line of "Regular Phase" microphones from the 80's and 90's are often referred to as "Printed Ribbon" microphones (and eventually even Fostex started using that term), and this is because they have a proprietary capsule design that has the coil printed, or etched, into the diaphragm. This makes the microphone neither a dynamic nor a ribbon by design, but some kind of a hybrid which has the same accurate phase response and pistonic movement of a ribbon, with the durability and SPL handling of a dynamic.
