Popping occurs every ~2 seconds

Troubleshooting audio is a bitch fam

Edit: Looks like it may be the tubes from what I've read on line. I'm purchasing a set of GE 6j1 5654 / 5654W / 6AK5 / 6AK5W tubes.

Hopefully they solve the problem and I dont have to start replacing the capacitors.

Edit 2: It was builder (me) error. I'd installed two transistors in the wrong place. Whoops.