You can convert a one valve bass trombone into a two valve bass trombone by selecting the 50B two independent valve option.
*On some models, especially those without a valve, the bell flange and socket may need to be moved upward or downward to meet the bottom bell brace of the valve section.
**Regardless of the number of valves on your 50B both the 50B(1v) and 50B(2v) will attach to your horn.