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In the early 1950s, RCA began developing a uniaxial ribbon microphone design that would be smaller and more compact than its predecessors. Built with a unidirectional polar pattern specifically for radio and television broadcasts, the BK-5A quickly became a trusted mic. The model was used for speeches by President Dwight D. Eisenhower, as well as radio performances from Frank Sinatra, Ella Fitzgerald, and Perry Como.
The BK-5A was quickly followed up by the BK-5B, another legendary ribbon microphone. The differences between the two mics are somewhat minimal, but check out the comparison chart below featuring information from archival RCA manuals.
Two standout features of the RCA BK-5A and BK-5B are their Blast Filter and Frequency Response Compensation systems.
The Blast Filter was specifically designed to protect the microphone from extremely loud sounds. According to the original RCA manual, it specifically safeguards against "gun blasts and other violent noises." This protection is achieved through two layers of acoustically transparent cloth supported by the microphone's metal grille assembly.
The BK-5A and BK-5B's Frequency Response Compensation is a fancy term for the microphones' selectable filter. Located on the bottom of each microphone, the filter is adjusted using a selector switch that requires a flat-head screwdriver. Three response settings are available: M (Music), V1 (Voice 1), and V2 (Voice 2).
With the BK-5B's Blast Filter in play, the ribbon mic handles extremely loud sources exceptionally well, including drums and bass amps. In particular, engineers often reach for the mic when tracking guitars, horns, and vocals. The BK-5B has that classic ribbon sound, smoothing out a source's harshness while delivering rich lows, silky mids, and smooth, natural highs.
Read on to learn more about the vintage RCA BK-5B currently available at Vintage King, professionally serviced by the Vintage King Tech Shop and ready for its next home.
Vintage King's Microphone Technician Tim "Timmo" Johnson recently spent some time servicing this RCA BK-5B. The restoration focused on cleaning the mic and addressing a few age-related issues that had accumulated over the years.
Timmo began by completely disassembling the microphone and thoroughly cleaning it inside and out. There was some corrosion built up on the mic's interior, so every component was carefully cleaned and restored before the mic was reassembled.
A couple of the BK-5B's original components also needed attention. The filter switch had stopped functioning properly, so Timmo disassembled, cleaned, and repaired it to restore full operation. Rather than replacing the original swivel mount, he repaired and refurbished it, preserving the original hardware and returning it to proper working order.
The microphone's cable had also seen better days, showing significant corrosion and physical damage. Timmo removed the deteriorated cable and fabricated a new short pigtail cable, finishing it with a new XLR connector that will have it ready for years of reliable service.
After reassembling the microphone, Timmo thoroughly tested the BK-5B to ensure everything was operating as intended before completing the restoration. And just like that, the microphone had been fully serviced and deemed to be in incredible working order.
