Hi there,the rect.tube could have gone because it's old and weak,or it could have gone because of a shorted cap or some other part.The tube probably had a heater open up on it,not short because your fuse hasn't blown,but you should check your fuse to make sure it's the right size.If everything pans out ok,then yes you can replace the tube,but since you've seen smoke,I'd look over everything.Good luck,Mel.