I'm working on a project for a friend where he has an old organ (4140 Wurlitzer) that was built in the 1960's. The schematics for it are no longer available. I've isolated the functionality problem to several TO-92 transistors on one of the tone generators. There is no part marking on the devices except for "891". Does anyone have an idea how to cross reference this to a part number? If not, is there an easy way to identify a potential replacement part?