I've purchased NOS tubes with success from tctubes, Upscale and Andy's Vintage tube services.
Some tubes I've needed that aren't that easy to find (6350 and 6C33C-B) I've purchased off ebay and audiogon. For those, 've sent them to tctubes for testing and believe me you get thorough test results and excellent personal service.
Some tubes I've needed that aren't that easy to find (6350 and 6C33C-B) I've purchased off ebay and audiogon. For those, 've sent them to tctubes for testing and believe me you get thorough test results and excellent personal service.