Seems like a spring issue. One of your keys is opening slightly when you play causing the fluttering sound. Most likely this would be the F#/C# key but could be any key held down under spring tension. Try pushing the pad cup down somehow while playing and see if it goes away.

-Jdbassplayer

I'll order the next size up, 1/16" thick instead of the 3/64 as mentioned above.
Cheers!

Why? That's just a waste of time and money...

Let me clarify how the key work functions. The lower joint is standard Boehm system. The only difference is that there is no linkage to the upper joint as there is no need for an alternate Eb. For the upper joint, Eb is fingered xoo|ooo. E can either be fingered oxo|ooo or by playing an Eb and using the first trill key or the sliver key. F is normal but F# can either be played with the first or second finger.

The plate with the vent hole is there to help with the altissimo like on bass clarinet. This is needed because the first finger tone hole is now a semi tone lower, meaning it is less effective to just lift the index finger. The plate is connected to the third finger ring so it will close automatically when you play an altissimo note.

Carl Fischer has been around since 1872, so 1896 is a perfectly reasonable date and I would see no reason to doubt it. Looks to be in very nice shape!

Yeah it looks like someone was going to convert them to the normal configuration with a barrel but never did. I have an Eb I need to do that to as well. Just try the mouthpiece right in the upper joint and see how the intonation is.

>Although he says at the beginning that everything on it was 3d printed, it's clear that the keys weren't.

Correct. I think I said it in the video, but just to clarify the keys (along with the posts and springs) are not 3D printed. Unfortunately while metal 3D printing has come a long way the technology is still too expensive. After speaking with a prototyping company I learned the cost would be about $500 per key, well above what a skilled tech would charge to make a key.

One promising technology is desktop CNC machining. CNC machining has been around for decades, however desktop sized machines capable of cutting German silver are becoming available. The Shapeoko 3 costs $1250 and works for this application. Of course you can only cut out flat pieces effectively so you still have to do a lot of soldering, but it does make building large amounts of keywork simpler. Making posts and screws are still best done on a lathe though.

In my experience, The no-name A clarinets really need a new register vent in order to play correctly. Otherwise you will be fighting a loosing battle against wide 12ths. Fortunately, a very effective register tube can be made out of a Nylon 3/16" OD bushing cut down so that it is about 2mm longer than the stock vent. These are available at both major home improvement chains here in the US.