[raduray]

Don't know anything about tube amplifiers. I've seen pictures of tube amps with pairs of large and small tubes and I assumed each one of the pair drives either left or right channel. But then I've seen others which only have one large and one small tube, and then even others with a single tube. How so those configurations drive separate left and right channels?

 

[Marutks]

Some tubes (for example, 6SN7) drive both left and right channels.

 

[HWB3]

There are preamp and power tubes. How they drive both channels depends on the design of the amp.

 

[EagleWings]

But then I've seen others which only have one large and one small tube, and then even others with a single tube. How so those configurations drive separate left and right channels?

These tubes have 2 x triode sections housed within a single tube and can act as 2 separate tubes.

https://www.superbestaudiofriends.org/index.php?threads/tube-amps-101-guide-for-dummies.12900/