A common complaint is that the low notes don't speak freely. For discussion, assume that you are faithfully practicing long tones in the lower register for the minimum of four hours each day; that you have the perfect reed; that you always keep your horn in key clamps when it is not being played; and that the moon is in the correct phase and the planets are in optimum alignment. Maybe it's time to consider a trip to the shop!
Here are a couple of modifications that I've made to customer's instruments (and my own!) that have gotten good results.
As you know, when the F, E, or D key on the right hand table is d
epressed, the F# pad (right above the F key) is closed simultaneously. This is accomplished by means of bumpers on the foot of each key which raise a bar which in turn closes the F# key.
The problem with this system is that the bumpers (cork or felt) tend to compress with time and/or the bar gets bent and out of adjustment, and you end up with a leak at F#. If this is the case, a solution is to place a "helper" bar atop the F key which gives the F# pad a little extra push. I first saw this done on Michael Brecker's Mk. VI when it was in my shop, and I tried it on my own Mk. VI and now I can't live without it!
The next modification, and probably the one that gives the best results, is to stabilize the lower
(C,B,B flat) keys. If you think about it you will realize that these keys have the largest diameter of any on the horn, and they are attached to the rod which actuates them at only one point. It is very common to find that the key has flexed from side to side and the pad no longer seats.
The solution to this problem is to add an additional rib which connects the key cup and the rod in a fashion which prevents the key from flexing. In
addition to assuring a consistent seat for the pad, I believe that this procedure gives a more positive "feel" to the lower keys.
I illustrate this in figure 2:
Of course, these modifications should be made ONLY after we are sure the horn is leak free, has good pads, and level tone holes.
Probably the number one complaint I get from players is that the G#
pad sticks. On "modern mechanism" horns (i.e. Selmer;
Yamaha; etc.) the solution is to add an additional spring that helps
pull the pad up when the G# lever is actuated. 
Presto! No more
sticking pad. The additional spring , a flat one mounted on the G# key
arm, is necessary rather than just increasing the tension on the G#
pad spring. This would result in the G# pad opening slightly all of
the time.
Some of my customers have had me modify the front F mechanism so
that the F and the Eb pad open simultaneously. This system was used on
the Holton Rudy Weidoft model horns, and facilitates some of the
altissimo notes.
Once I get the key heights adjusted, and a proper mouthpiece
selected, the Battle of Intonation begins! The notes C#3 and above are
notoriously sharp, and I have had great success in fabricating an
additional mechanism which changes the venting of the C# pad in the
upper register only and greatly improves the intonation of all of
these troublesome notes.
