I have 8', Sylvania T12, 75W tubes (2 each) in my shop fixtures. The
other day one of the tubes quit working. I replaced it with a used
spare I had and it worked but appeared to not be as bright as a new
tube would be.

Today I bought a box of new tubes that are exact duplicates of what I
had

http://www.menards.com/main/electric...33660800703824

http://tinyurl.com/oswn9a7

and replaced both of the above tubes with new tubes. Neither new tube
would start properly, they flickered and hummed and would only produce
about 1/2 of the expected light output.

I moved the new tubes to another fixture and had the same results. I
replaced one new tube with a used tube and the used tube worked fine
and the new tube still flickered and hummed and produced 1/2 the
expected light. The results were the same in a third fixture. All in
all I tried variations with six of the new tubes and none worked
properly.

I don't have any spare ballasts to test for a dying ballast. I'm not
sure how old the ballasts are, maybe 10 years old. Could the ballasts
be the culprit or did I get a box of bad tubes?