Tube Questions

My DAC uses 12Au7s and I see that I can use 5418As, as well as 7316s. What is the difference between a tube that is made by the same manufacturer, say an Amperex Bugle Boy where one seller lists them as 12Au7s and another seller has them listed as 7316?

According to the substitution guide book by Middleton:
12au7a, 5814, 6067, 6189, 6680, 7318, 7730, B329, E82cc, Ecc82, Ecc802, M8136 are all excellent subs for a 12au7.

Good subs are: 12at7, 12ay7, 5963

Middleton has never failed me yet. Don't see 7316 nor 5418A (assume it is heaver duty than 5418.
The 7316's are premium 12au7's made by Amperex. You can use the 5814s without a problem, in fact, likely the second best 12au7 variant is the CBS/Hytron 5814a Square Getter double Mica, circa early to mid 50's.