The post in the old 2013 thread is not very accurate from what I can see. Most of the D&RGW engines that have a single NOTE whistle today are D&RG or D&RGW hooters. Not every hooternis a star brass.
What Stathi was doing was tuning the whistle. The same whistle can be used on different engines and at different pressures, but needs to be adjusted for each pressure. Single note whistles often have a center stud that the bell threads onto. You can raise and lower it to adjust for different pressures.
When 315 borrowed the hooter from knott's it was not properly tuned. In between photo runbys Joe Daily tuned it and to sound much better.
Jeff Taylor
CRRM curator of equipment and rolling stock.