Can using a bad tube hurt an amplifier?

Sounds like voltage changes if they occur from a tube should be corrected by the auto bias?  

Yes, I just had this happen to me: everything working fine for 4 months with the 300b Gold Lion’s in my Coincident Frankenstein stereo amp. The amp and tubes are both 4 months old, I haven’t touched anything in weeks, and I turn it on a few weeks ago and one 300b tube is much brighter than the other one. By the time I got to turn it off I hear sizzling bacon, I shut it down and witness what appears to be plenty of smoke bellowing from the amp. Israel Blume Coincident owner says the tube has "run away" which I believe is the same as "red plating" as stated above. I have no way to check tubes so I sent if off to the retailer and they have checked it and confirmed it is bad, warrantied it, and a replacement tube is on the way back. There is a 1% failure rate and I am one of the lucky ones.

There is automatic bias circuit in this amp so nothing to adjust on my end, but no special protection circuit to shut off the amp in the case of a faulty tube, not sure how many amps have this? 

No warranty for the amp as it was the tubes fault. Easy fix though thanks to point to point circuit wiring. 

The joys of tube amps I suppose. 

  I had this happen about 5-6 years ago with my Had Inspire SEP amp. It’s auto bias for the two power tubes and also will take multiple value rectifier tubes allowing me to raise or lower the voltage. It takes EL-34 to KT-150 and I can run any combo of power and rectifier tube. I had a new pair of GL KT-77’s that were at approximately 100 hours. I heard a loud pop from the amp and a really loud bang from my left speaker. I immediately hit the power switch and saw a wisp of smoke coming from inside the chassis. The tube never changed appearance when this happened and the left channel went dead. I took off the bottom plate and discovered the entire internals were coated with paper, oil and foil from the explosion. Also a large resistor exploded and together they generated enough force to break the terminal strip that the circuit was attached to. I shipped it to Dennis for repair and included the two power tubes for him to test. He confirmed that I had a “ Run Away “ tube. The vendor refunded the tubes and I paid for the damage. Another time I had a 6550 tube pop due to the glass envelope failing. I heard the sound and turned off the amp. The tube had a fracture that ran top to bottom and was completely white on the inside of the glass. There was zero damage to the amp, and I just replaced the one tube. Shit Happens when you run tubes, it’s part of the lifestyle. Cheers , Mike B. 

The problem I had was the tubes were fine for several months.  And then one day within 20 minutes one of the tubes started over heating and glowing alot more  it wasn’t the glowing tube that was the problem it was another tube in the same series, since they’re all connected.  all the tubes test fine it’s just that one of the tubes begin having voltage problems after 20 minutes. Very difficult to diagnose when you have many tubes.

There’s no way to predict this.  These were NOS tubes, presumably supposed to be higher quality than the new stuff.