There are a couple of possibilities.
One is that the tube just needed a good re-insert and everything is fine now.
Another is that a pin on the tube was damaged when bumped. If so the tube needs replacement.
The least desirable issue would be the bump damaged the tube socket. This is unlikely in my experience. While the part is not expensive, that is a service call item unless you are very comfortable with using a soldering iron on the insides of an amp.
If you have a dead channel again, switch the tubes from the left channel to right and see if the problem follows the tube. If so, replace the tube. If you continue having dead channel issues in the original channel, have the amp checked by a technician.
One is that the tube just needed a good re-insert and everything is fine now.
Another is that a pin on the tube was damaged when bumped. If so the tube needs replacement.
The least desirable issue would be the bump damaged the tube socket. This is unlikely in my experience. While the part is not expensive, that is a service call item unless you are very comfortable with using a soldering iron on the insides of an amp.
If you have a dead channel again, switch the tubes from the left channel to right and see if the problem follows the tube. If so, replace the tube. If you continue having dead channel issues in the original channel, have the amp checked by a technician.