Old valve bass amp crackling

Try cleaning the tube sockets and tube pins. This is often a source of noise in older tube equipment caused by oxidation on the metal contacts. Use a good electronic contact cleaner and gently brush the socket contacts with a pipe cleaner or similar tool and clean the tube pins with a cotton swab.

If that doesn't do it you could have some coupling caps getting leaky but I'd bet on dirty sockets.
cleaning tube sockets

Just a quick question since I have a similar problem with an old Calrad sa30b amp. I do have another thread going on my issue under "...distortion..."

How do you clean the tube socket with a pipe cleaner? My sockets are tiny! Are there pipe cleaners or similar tools that can get in there?

Thanks from an aspiring diyer,