I decided to work on it partly to have a working instrument to play about with while my concertina is in bits being restored, and partly so that I could practice the skills involved in tuning reeds on a relatively cheap and unimportant instrument before I tackle those in my valuable antique concertina. The tongues are made of brass rather than steel and they are held by one rivet each to a single big plate with multiple slots cut in it rather than clamped to individual frames with pairs of screws, but the principle of tuning is the same. To raise the pitch you file a tiny amount of metal off near the tip; to lower it you do the same near the root.
There were a couple of completely duff notes (it was like that when I bought it; it was a cheap "spares or repair" eBay purchase), and nearly every reed was out of tune (mostly flat), some by up to 50 cents (half a semitone). When I opened it up I discovered that many of the tongues have cracked next to the mounting rivet. One of the duff notes was caused by a reed that had rotated slightly and was fouling on the edge of the slot. The other had come a bit loose: a few carefully-aimed taps with a ball pein hammer tightened up the rivet enough for it to speak, though it still sounds slightly muffled.
Filing the reeds to adjust their resonant frequency turned out to be pretty easy (I was glad that I recently splashed out on a top quality Swiss very fine half-round escapement file; it produced a much smoother finish than whatever the factory tuner had scratched at them with). What I found difficult was measuring the errors, because:
- I wasn't able (not for want of trying) to sound the reeds at an even vaguely consistent pitch without fully assembling the instrument and blowing through the mouthpiece, which meant replacing 13 screws. I must have done this about thirty times, gradually stripping several of the screw holes in the process (it uses a wooden sound board and tiny wood screws). When I do the concertina reeds, the bellows bench should help with this problem.
- Even with the instrument assembled, it's easy to bend the pitch by +/- 15 cents or so just by modulating how hard you blow into the mouthpiece. Maintaining a consistently moderate breath pressure over 25 different notes is easier said than done.
- The reeds seem pretty unstable, some worse than others. The cracked mounting holes are probably mostly to blame for this, though I suspect it doesn't help that when you first play a note your breath causes the reed to warm up and become wet from condensation. One reed in particular seems to randomly go ten to fifteen cents sharp then back into tune for no apparent reason. Tuning that one was 'interesting' because filing it even by tiny amounts caused it to change pitch wildly and unpredictably. Two or three others suddenly jumped pitch by fairly large amounts when filed, probably more because the rivet moved rather than because of the removal of metal. Hopefully the concertina won't suffer from this problem because the tongues are much more securely mounted to the reed frames.
In the end I got all the reeds within a couple of cents of concert pitch (equal temperament, A=440Hz) when you blow moderately hard and when they all feel like behaving. The volume and tone varies a bit and I'm not confident that they will all still be in tune tomorrow, but I don't think there's much I can do about that, short of replacing all the cracked reed tongues. It's certainly not a professional grade instrument but it should be good enough for a beginner to play around with. I also now feel much more confident about tackling the concertina tuning (the part that still worries me is maintaining a consistent air pressure because of the pitch bending problem).