If your charger doesn't work without a nattery load then you shouldn't ever power it without a fuse. That is because there is enough energy in the battery to give one serious burns if there is a short.
Do you have a volt ohm meter? If not you really need one. They can be had for less then $20. I can then describe how to check the heater in each tube. However, I think that powering it up first without the vibrator would be good.
