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Hope this is helpful.
T&E #13: MAW Valves

The MAW valves on the 2165 I recently sold were fantastic. Lighter than the factory valves and better made. That made for a fantastic feel under the fingers.

On that tuba, which wasn’t really known for an “open” low register, was immensely open and even in the low register. The fundamental C to D just above it was a smooth and easy slur with, as noted in the video, little to no change in timbre despite over a dozen feet of tubing being added.

Definitely worth considering if you have a great tuba that you wished were a little more open and even. Note, I wouldn’t expect any change in intonation. Possibly the slots feel different, but the bugle characteristics are unaltered.

I'd add that these, in my experience, are a significant upgrade for some tubas, but generally "okay" for others. For tubas like the 5450, with an already great low register, they were less exciting than in something like a 2165 or a Hirsbrunner.

I appreciate Chris' time for another excellent evaluation. I wonder his thoughts if he were to put these in an F tuba. Depends on what you've got, I guess!

In my Bohm & Meinl, they absolutely help the low register of the 4 piston limitation.

Where they really excel is in the weight department, particularly for MW/B&S big valve tubas. The weight savings are so noticeable for those tubas and hand fatigue simply goes away.