Thanks to Gary Kern for letting me review this clarinet!
Bore LH joint top: 14.6mm
Bore LH joint at bottom: 14.6mm
This Monopole is a lot different from the better Monopole I reviewed which I still do not think was made by Couesnon.
Gary found this interesting information from woodwind.org ClarinetBB:
Serial number 18900 - 1952
Serial number 28500 - 1960
At the rate of 1200/year, that would date mine around 1944
This clarinet has two pads for the one F/C key as seen below. The second key cup is not hinged separately. Both pads come down together. The second tone hole is just to allow for a second vent hole. The hole for the second pad is actually quite small, a little smaller than the ringless hole on the left hand joint. There is wide beveling around this hole in order for it to accept a large pad.
I think that this was designed because the G/D is often a fuzzy note— if the F/C pad is adjusted nice and close to the hole. The normal distance of 3mm often results in fuzzy G and D. Having the extra vent hole allows the two pads to be adjusted even closer than 3mm to the tone hole. This means that one does not need to move the key so far, and this would allow for a little better action in some quick passages.
Note also the extra long Ab throat tone key!
[Update 7Dec14] Thanks to Tony in Charleston for this interesting info:
Phil, I have 2 Couesnon Monopoles. One is only a few numbers from yours (10276) and has identical key work. The other is a Conservatory (20341) that dates from about 1953 (as do I). That one has the dummy 7th ring on the C/G hole with no roller and no second F/D vent. Both had exactly the same wonky tuning issued you found. I tried a Portnoy MP, and it was better, but not good. After a lot of fiddling, it turns out that the long notes are seriously over vented. Reducing the pad lifts with some strategically placed corks dramatically improved low note tuning without screwing up the clarion. There is a thin line between in tune and stuffy, but when it's right, these play really well. They aren't quite as in tune as my Leblanc Symphonie 3, but they blend easily with the community band, most of which are members of the Buffet Mafia.
Intonation results taken when playing loud and not lipping. See how to interpret these results on the Model Comparison Page.
For this test, I pulled 1mm at the barrel and 1 in the center. For the first test I used a Chedeville Prime (my second one) and afterward I realized that that mouthpiece does not play nearly as well as my first one. I have returned both of them for analysis. The second test was done with a Portnoy BP02 mouthpiece on which I know that my throat tones are always much lower.
Intonation summary: [My first reaction] In spite of obvious signs that Couesnon was trying to make a professional instrument, this does not arrive at professional intonation in the era that it was made. I should have pulled more than 1mm in the middle and at the barrel. But even pulling more, there are areas of the instrument that are too sharp. I have found some Couesnon instruments that are better. [My second reaction] Wow, what a difference a mouthpiece makes! If one uses the right mouthpiece it makes a whale of a difference. The Portnoy has a 14.8mm bore, and that could be one part of the difference, since I think the Chedeville is 15mm. I will have to check when I get them back. One could definitely play this clarinet in tune with the right mouthpiece.
Key work quality: The key work is better than many Couesnon instruments. Consider the roller for the Eb key, and there is the long throat tone Ab key, plus the special F/C double key. The Ab throat tone key has an adjustment screw, and that is unusual for Couesnon. The tone hole for C#/G# (left pinkie, at the bottom of the LH joint) has no beveling. I now think I know the reason: There just isn't enough room before the end of the joint (before the cut that goes down to the tenon joint). Beveling would go past the end, and this could cause the drill bit to chatter and chew up the hole.
This clarinet is most appropriate for: An intermediate student or adult.