Posted by Ray on December 31, 1998 at 13:53:41:
In Reply to: valve porting posted by Jon on December 31, 1998 at 10:04:27:
The effect of porting a rotary valve allows you to pull the slide without building up pressure (tuning the first or other valves). I have ported the valves on two tubas and would recomend that you have someone do the work who knows the right place to make the hole. If the vent is in the wrong place or is too large, the valve may leak.