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I have an old Gon Bops conga 11", and found a quinto 10 1/2" of the same type as mine on Ebay. It is not a perfect fit, but i suppose there should be no problem tuning them to a good interval and still get the optimal sound from both. I also have a 10" quinto of unknown make, so it would be interesting to see if the new drum (if I get it) will fit with those two.
Another thing that might be of interest to some people here: there is another vintage conga on Ebay. Unidentified object, sold as a bongo. Search for vintage bongo.
Merry Xmas to you all. casaet.

FYI: The original pre-DW Gon Bops quintos were 9.75" and their congas/segundos were 10.5". The congas and tumbas came in a number of larger size variations, typically designated by "L," "XL," "2XL." On the badge you'll see things like "IC-3014" for a standard 10.5" conga, "ICL-3014" for a slightly larger one, and then things like "ITXL" for an extra large tumba. (The "I" might stand for International Series - not sure.) To my knowledge quintos were always just quintos, like "IQ-3014," and never had a larger version.

Taiko is right, 10 1/2" is a Gon Bops conga.
Gon Bops catalogue:

I've got an oak 10.75 gon bops and I really think it sounds much better for rumba than in a traditional salsa setting, not enough meat, much more of a quinto sound than a drum for playing marcha.
PC

I've got one too. I also use it mainly for rumba, as a tres dos.
But I've used it for jazz too. I think it works well with both.
Mine doesn't sound good as a quinto though. Maybe it's the skin.

Could be, I've got a mule skin on mine, and though it sounds fantastic when tuned high and tight, it does not have a lot of sustain and warmth at lower tensions. I guess that's why folks like them on quintos but not so much on smaller drums.
PC