It depends on amp's circuit design more than on type of tube being used. Most of SETs are using primitive amature DIY design, but tubes in SETs last quite a long time before anything serious can happen. There are ways to prevent bad tube to blow:
1. Turn off tube amp when you're not listening to it. It takes only 5m to get tubes to the normal operation.
2. Eyeball the tubes having a normal glow when you play the music. One tube that will glow too bright or too dim might not be normal.
3. If you hear microphony, inspect tubes.
4. Have extra set of tubes. It helps you to check if problem goes away after you swap for the fresh one.
1. Turn off tube amp when you're not listening to it. It takes only 5m to get tubes to the normal operation.
2. Eyeball the tubes having a normal glow when you play the music. One tube that will glow too bright or too dim might not be normal.
3. If you hear microphony, inspect tubes.
4. Have extra set of tubes. It helps you to check if problem goes away after you swap for the fresh one.