Re: YBB641 valves, Pleeeeeease, HELP!


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Posted by Steve Dedman on March 22, 2001 at 20:20:49:

In Reply to: YBB641 valves, Pleeeeeease, HELP! posted by DS on March 22, 2001 at 18:09:42:

Unibal-type linkage can easily be adapted from model airplane parts. You might be able to machine something a little more durable. The problem is that a 641 is not as great of a candidate for conversion if it has the old-style pin-and-hole linkage, where the screw actually goes through the valve stop and linkage arm.

Another possibility is to manufacture a taller bridge, and extend the length of the spatulas. As I recall, the bridge that holds the valve spatulas and springs on a 641 is a little too short, IMO. By raising the bridge (and adding a thumb ring), a mechanical advantage is gained. The valvestroke is shortened a little, so the drawbacks of tighter springs are lessened. I'd talk to a pro repairman about that, though.

If you don't wish to perform major surgery, you might (after a thorough cleaning) try varying the weight of the oil you use on the bearings and races. You'll just have to figure out by trial and error what weight is best.

If you have the older pin and hole type linkage, check to make sure that the screw isn't torqued down too tight. It can actually be tightened down enough to lock the valve. Of course, this is a delicate balance between optimal function and having your own built-in percussion. If you end up loosening the screw, and it bangs like crazy, you can put a drop of 3-in1 oil on the screw and stop to cushion the linkage and maybe quiet it down a little.

Also check the back plate to make sure it is pressed in evenly on the back of the valve, and that maybe a tap to back it out ever so slightly might also help.

Lastly, check that no schmutz has built up in the back screw-on cap. As you may recall, Miraphone has a set screw in the middle of that cap to adjust tension. The 641 doesn't have that set screw, but gunk can build up in the recess of the cap and perform the same function, which in this case is unwanted.

With the older 641 valves and linkage, it took constant tweaking on my part for quite awhile to find the optimal adjustments. Be sure you remember what you do and when, because once you take a valve apart to clean it, you really want to get in the ballpark when you put it back together.

Steve "who waged this war daily in high school" Dedman


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