I bought recently a pair of used globe power tubes. They both checked out fine, tested them on my radios. Bases are tight. What concerns me is that there are some flakes inside the tubes when one turns them upside down. Can I keep them or send back?
That would be the material used to coat the filament so electrons are given off at a lower filament temperature. I have found over the years that tubes that have been abused electrically, ie: over heated due to bad caps, tend to do this. I have also noticed lately that some of my NOS early globes are doing the same thing and they have never seen any service so not sure what to make of it. The biggest problem with this is this material can cause a short in the tube if it gets between a couple elements.
Gregb
That's very common in rectifier tubes and not worth worrying about. I would be surprised if I didn't find those flakes of cathode coating in my 80's.
I also have those flakes in some 45 and 47 globes. What kind of the worst scenario damage may occur while using them?
Prrobably OK, especially if kept operating in standard vertical position, base down. Might not like service in a helicopter or at sea.