When sockets are new, they might require a lot of force to pull a tube out, in which case pull from the tube bass if it's an octal or 4-pin. In lder tubes, sometimes the glue that holds the glass envelope has dried out and lost strength.
Paramount in 2A3 form (now discontinued), if recent production v1.1 or with the soft-start upgrade, should rest for 20 minutes before re-starting. It's in the manual (p.67 for Paramount), but not everyone reads the whole manual, or remembers every word in the manual.