Restoration Examples Page
RCA 77-DX & RCA BK-5B Ribbon Mics - (See below
for the "Before" & "During" pictures)
The "After" Pictures:


AND: An RCA BK-1A Dynamic & KS-11 desk stand:
The BEFORE & DURING Pictures of the above 77-DX
& BK-5B:
The pictures don't really do justice to how bad these
were. On the 77-DX, the surface rust on the center label ring meant
removing the nickel plating (note it's brassy appearance in the disassembled
picture below), as did removing the rust, oxidation & pitting on the
shock mount parts, yoke thumbscrews & cable clamp. This mic prompted
me to learn how to do auto-catalytic nickel plating. On the center
body, which is a bakelite cylinder that is riddled with holes inside to
form a transmission line labyrinth, the top section had been covered with
a piece of copper sheet metal, to hide a 2.5 inch long section of the top
edge that was chipped out. I removed the plate & re-constructed
the chipped out section, then primed & repainted the entire body (to
the proper color). The bottom housing was pitted from oxidation so
badly that I had to get it sandblasted. Then, I polished back to
it's original shine.

The BK-5B shows it's damage pretty well. It was
mainly just a matter of stripping every bit of paint off of every part,
polishing out the oxidation pitting, then priming & painting.
The trickiest part of doing a BK-5 is the ribbon installation & tuning.
It's ribbon has a width of 0.052", vs the 77's 0.056". Not a big
difference, but the BK-5 has much less clearance between the ribbon &
the walls of the magnet gap, making it much much harder to keep perfectly
centered during clamping & tension tuning. In the pictures below,
note the ingenious use of the outside wall of the BK-5 center body to create
the labyrinth, necessitated by the fact that the transformer & low
cut inductor occupy the middle space.

