testing tubes similar numbers

[timmy]

hi all i have a 6dq5 tube to test but i only have a listing for a 6dq6 could this be tested. and others with the same 3-4 digits but with some other letters on the end confuses me as to if i can test tubes with extra digits on the end, or should the first 3-4 letters or numbers be the same to test no matter whats on the end.