10-30-2019, 11:42 AM
I am always on the lookout for the early metal tubes - with the bump. Almost all of the big manufactures, less Philco, used them in 1935. Many quit in 1936. The earliest ones showed up in 1932. They had stamped labels on the upper tube body until about 1936. I have found most metal tubes (after 1934) to be equal or superior to glass, if for no other reason, shielding.