FWIW, Don't know about the 6l6, but I have used Westinghouse labeled Sylvania 5v4 rectifier tube with great results, and have some shortplate Westinghouse yellow print/yellow star 12ax7's that sound great, that particular 12ax7 is a fave of Bob Rissi, a major guy formerly working for Fender, the designer of Risson boutique amps and the Rickenbacker Transsonic amps used by Led Zeppelin in their early days on tour.
