Hello:
Restoring that Firestone 13g3 I picked months ago. Its missing most all tubes:no: I have all needed except the 6SL7 plenty or any other 6S*7s but not what i need,is there a sub I can get by with untill I get a 6SL7, so I can test the set out thanks!

The 6SU7 is a direct sub. A 6SN7 *might* work, if your Firestone is NOT a series-filament-string TV set. The 6SN7 draws more current and has less gain.

Any other 6S*7 I wouldn't try.

You might find these pages useful:
http://www.duncanamps.com/tdsl/show.php?des=6SL7GT
http://www.nj7p.org/Tube4.php?tube=6SL7gt