Just as a point of interest, I have an RCAF BC-456 which has been modified with both a sidetone level pot, and a microphone level pot. The modification tag on the side shows B!,B2, and 3. Which leads me to wonder if anyone has ever put together a complete, all RCAF SCR-274N system, or for that matter a complete Colonial made SCR-274N system? Jack Antonio WA7DIA