I recently acquired a vintage RCA Radiola 106 loudspeaker on ebay. This was the speaker that RCA used for its 1929 theremins. I got a reasonably good deal on it because the tapestry on the cabinet was badly damaged but I didn't want the cabinet anyway - I only wanted the speaker with its coils and assembly, for installation in Samuel Hoffman's instrument.
Dr. Hoffman replaced the 106 that had been in his instrument originally, with a standard GE replacement speaker sometime in the early 1950's. The 106 is an extremely heavy unit (about 20 lbs) and must be plugged into a power source. The RCA is supplied with a separate power receptacle specifically for the purpose.
In any case, the 106 I bought on ebay turned out to have some minor issues with cracks in its cone that interfered with with the sound production. The cones were made from a heavy, black paper/cardboard that most of you are probably familiar with. Over the years the paper dries out and eventually begins to disintegrate, much like the paper in old books.
Since there were no holes in the cone, only hairline splits, I decided to attempt to repair what was already there rather than having the speaker re-coned with entirely new material. I figured if my repair job didn't work, cone replacement was always an option.
I found the following video on YT and followed the instructions to the letter, making the repairs with carefully cut out coffee filter paper and diluted Aleen's ORIGINAL TACKY GLUE. The results were excellent and the speaker works like new!
If anyone here wants to restore a vintage speaker, I strongly recommend the methods and advice in the following video.
