I notice that a Swan 250 six meter rig uses 6146B tubes in the final. What I'm wondering is if what Glen has stated about the swapping of 6146W tubes for them in Heathkit HF rigs also applies to the 6146B and W versions being swapped in the Swan six meter rig ... i.e. the W versions can sub for the B depending on the manufacturing date of the W? Ray wa7itz