Unintended tremolo

[AHS]

I have an inexpensive (entry level) Weltmeister 607 Anglo Concertina DG 20 on which I've been learning.  While it is not a high quality instrument, it has been working adequately for me and the notes all had a pure tone.  Suddenly, today, I noticed that it had developed what I can only describe as a tremolo.  The notes seem two waver across a small harmonic range, or perhaps there are overtones on both the D and G rows.  It is most pronounced when I'm expanding the bellows but I think I also hear it when compressing the bellows (although I'm less sure about that).   I took off the plates on both sides and examined both reed boards and I also blew them out in case dust had lodged in there.  I didn't see any obvious problems.  When I put it back together, it seemed to play normally for a little while and then the problem came back.  Any ideas would be much appreciated.

[robert stewart]

This may be an obvious thought that you have considered already. Do you have a ceiling fan or other kind of fan running when you play and notice the vibrato/tremulo? That frequently causes a tremulo effect for concertinas. Which is not there, of course, when any fans are off.

 

best wishes, Robert

[Frank Edgley]

If not the ceiling fan, then I suspect those two notes are a bit loose and vibrating at their seat. If it occurs only when expanding the bellows it suggests that the negative air pressure which occurs when expanding the bellows would tend to pull the reed(s) away from their seat on the reedpan, and cause a very slight vibration. I am not familiar with the Weltmeister, but I suspect there reeds are waxed in. Examine the wax around those two reed plates. There may be a very fine spacing or crack around the reedplate, which may or may not be visible. If that is the case, it should not be difficult to put it right.