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Ok... before leaving work, I was putting some tools away in my rolling tool chest, and noticed a Craftsman Vernier Caliper ( at least 40 years old, so it's quality USA-made ), no dial-indicator, but a Vernier scale that reads to 1/1000 of an inch. ( 0.001 ).

I "mic'd" the bayonet hub of the Columbia reproducer that I found on my desk: the hub/neck is ¾" dead-on: 0.750".

I brought said reproducer and arm home, and pulled-out my "New Columbia" sound-box, and tried that in the old-style arm: fits fine.

I then went-up to the attic, and tried to get the #6 Columbia soundbox off my 1914 "Jewel", and it is seized on the arm.


At any rate, my initial take-way on this is that "all" Columbia bayonet-mount soundboxes are interchangeable.

This is not necessarily so at the back end of the arm, where it mounts to the elbow: there IS variation here.


If you have several different bayonet-mount Columbia boxes, and NONE of them will fit your arm, my guess is that the socket on the arm is swollen-closed a bit, and needs to be relieved. Remove the horse-shoe spring and pin while checking fit.

Suggest you get a decent Vernier caliper or micrometer ( available at Sears, Lowe's, Home Depot, Harbor Freight ), and carefully measure the mounting hub / neck on the backside of the soundbox. If the hub measures ¾" dead-on, the hub is probably okay - don't remove any stock from it. Instead work on carefully removing a little material from the inside diameter of the socket.

Good luck !

Frank

For the good of the order, I am reporting back after playing-around with a few of my reproducers, arms, and circa 1912 Grafonola "Jewel".

I will attach photos of the reproducers I have mentioned in my posts above.

I went up to the attic, where my 1912 "Jewel" currently lives, and removed the whole tone-arm base, arm, and reproducer, and brought all down to the workbench.

The loose arm and reproducer I brought home from the work desk are probably post WW-I, an un-marked No. 6 reproducer, with the big strut connecting the needle-bar pivot bosses. The reproducer and the arm are both pot-metal.


The arm from the "Jewel" turns-out to be brass. The reproducer has been stuck in it since I got the machine. I summoned-up some courage, and put the arm and reproducer in the freezer overnight. This morning, I removed it, wrapping in a dish-towel, and tried turning the reproducer: still stuck. I though a minute, then ran hot water over a dish-rag until it was almost too hot to handle, wrung it out a bit, then grasped the end of the arm by the reproducer socket, waited a moment, and tried turning the reproducer again.... this time, it broke-free, and I was able to take it apart !

I put things aside, to return to room temp, and when I came back the reproducer, I noticed it had writing cast-into the back of the body, around the mounting hub, but concealed by the "skirt" on the arm when installed on the machine. It reads: "Patent Applied For" and "No. 6 ".

I cleaned-up the mounting socket in the arm, removing a few burrs around the hole of the locking pin, and then began to fit the reproducer - it would go into the socket about half-way, then begin to bind. I carefully, slowly sanded the interior of the socket, and the hub of the reproducer, using 400 then 600 grit wet/dry paper. For final lapping, I smeared some Colgate toothpaste around the hub, put it into the arm, and twisted a few times... it loosened right up.

Cleaned-out the toothpaste, and applied a little petroleum jelly, and it's as good as new.

All three reproducers, early No. 6, later No. 6, and "New Columbia" all fit the brass "Jewel" arm, although the later reproducer hubs are a little bit tight.

All of which does not necessarily help Doug, but does seem to confirm that from at least 1912 onwards, the bayonet-mount Columbia reproducers should be interchangeable...