I recently came across a box of old vacuum tubes from among my grandfather's things. They range from 7N7s, to all kinds of other tubes for TVs and radios. Only 5 were usable in guitar amplifiers. All are USA made RCA tubes from what I can tell. 5U4GB 6V6G 6V6GT VT-107-A 5Y3GT I don't have or have access to a tube tester. I've visually inspected all the tubes and the 5Y3GT is probably bad (rattles and the base is loose). The others check out. No white inside around/at the getter; no other discoloration. No rattles. I've cleaned them up and cleaned the pins. What else can I do before I plop them in a known-good circuit and see what happens?