12at7 or 12au7
 

Does anyone know which tube 12at7 or 12au7 has more gain.

The 12AT7 has a higher mu, therefore higher gain. The circuit should be designed around it.

They are for the pilot tv so I was wondering why it don't have all that good of sound and picture, I have 12au7 in there so I'm sure it will improve with the right ones, it was designed for the at7 s.

I had to look at the schematic, the set uses three 12AT7's. The 12AU7, never did make a good tuner tube. Even if you have a 12AT7, that's a little weak, it's still better than using a 12AU7.
Once in a while, the tube sub guides, can lead you down the wrong path. :sigh:

A 12au7 has a gain of 20, 12AT7 is 70, very different tubes. Surprising it works at all with the wrong one. 12ax7 is closer to the AT7, with a gain of 100.