human
Considering the provided database schema and associated query, produce SQL code to retrieve the answer to the query. 
###Database Schema: Driver Unit Model No., Release Year, Output Voltage (RMS), Inputs, Outputs, Notes
###Question: What year were outputs is 2x pro bias, rca loop out and notes is vacuum tube released?
gpt
SELECT Release Year FROM table WHERE Outputs = 2x Pro Bias, RCA Loop Out AND Notes = Vacuum tube