So I have a Trombone that’s been in my possession for awhile now, but I have yet to figure out exactly what model it is. It is a Bach trombone with the serial number 27307. When I check serial number charts online, it shows it being a 1977-78 model, but doesn’t tell me what the actual model is. Does anyone have any clue? I can post pics if needed. It is a small bore, has a smaller bell (like a tenor peashooter), but has an F-Attachment. Also doesn’t have an arm mechanism for the spot valve, but has an enclosed, spring-loaded, push valve.