Need info on a Ken-Rad 5z4-MG tube


I had this metal can for some time now and wanted to see if anyone could help with more info. This monster of a tube is 4.5 inches long and about 1 inch in diameter. The entire can is perforated with holes I suppose for heat dissapation. All the metal tubes I've seen do not have these holes. I have yet to try it in my pre as I hear a slight noise when handled. Strange to me but may be common to others. Unable to test but don't want to trash it just yet. Thanks in advance.
FWIW, my older Sam's Tube Substitution Handbook lists it as two-way interchangeable (meaning either can be substituted for the other) with all other versions of the 5Z4, as well as the 5CG4. The 5V4GA, 5V4GY, and 5AR4 are listed as substitutes for it, but not the other way around.

-- Al
Hi Al,

Thanks for your response. I wish I had a way to test it for shorts etc. It sounds like something is loose when turned upside down. Even with the holes it's hard to see the inside. Perhaps I'll find someone that can take a look see.
Regards and good listening,