Vintage RCA Ribbon Microphone PARTS LOT. RCA BK 11 Ribbon Microphone Bottom Base – Looks like Original Paint. Pair of RCA BK-11 Grilles in Very Good Condition but will need the metal band to be re-attached to one of the grilles – (usually is spot welded or soldered) – see photos and new grille cloth. RCA 74B Bottom Base – has some metal missing on back side – see photos.