Interestingly, I have exactly the same problem but maybe my recent experience will help. I've got a 200A, 1980 and I've removed the action from the piano and have it on the bench in a jig. One of the things I discovered was that there were two reeds missing (21 & 22). I recently ordered them (complete with new screws and washers) from our UK supplier of Vintage Vibe parts. They are supplied without the solder pyramids and you need to make your own. VV sell a mould for this but I didn't want to pay for that with only two to make so I made my own using an adjacent reed as the model. They turned out really well and I rough-shaped them before the tortuous process of fitting them. First problem - tinning the reeds is difficult to get right and this needs to be perfect before trying to attach the pyramid. First, the base of the pyramid needs to be perfectly flat. Attaching the pyramid to the reed is the really tricky bit - I stuck the weight on the reed with flux, held it in a croc clip then heated the underside until the solder just flowed at the base, then removed the heat. The pyramids seem firmly attached and have been rough-filed in preparation for final tuning later. Here's the thing, I re-mounted the two new reeds and one sounds nice and clear and rings like the others. However, the other one sounds exactly as you've described - dull! No volume and no sustain. The ONLY difference I can think of is that the pyramid on the 'dull' reed is somehow attached imperfectly. The washers are the right way up on both and I've not overtightened the screws. So maybe it's a dry/imperfect joint thing causing the pyramid not to be completely stable, thereby damping the oscillation of the reed. Or maybe there's an air bubble in the pyramid. I'm going to investigate further and post the results when I get time. BTW, all my other reeds sound good and there are only a few with 'perfect' pyramids. Most of them are a mishmash of shapes but it seems to make no discernible difference to the sound. Sorry for the long-winded post but I hope it's of interest and we can find out the cause of the problem.