Make sure all the tube pins are making good connection in their sockets. Sometimes it’s easy to over-loosen the sockets when assembling. If pin 2 (the plate) wasn’t making good connection then the screen (attached to the 2k2 resistor) would start drawing too much current. So tighten all the tube sockets.
…But I’d start by turning on the amp without the tube in the socket to see if the problem is just related to the tube and/or socket.
Keep me posted on what you find.
Good luck.
-Brach