30 seconds of fireworks! I am surprised the 5AR4 did not short out altogether and blow a fuse. It would seem your rectifier is going! In my experience, when a rectifier fails, it has blown the IEC fuse and not damaged the amp, though maybe I have been lucky. I am thinking I recall seeing that Steve has started using fuses inside some amps as well, I am guessing for double coverage??? Anyway, I would get a new pair, and in the meantime, I would pull the suspect pair you have in, and use spares until the new ones come.

Yes, if a rectifier arcs more than once or twice when it is new, then consider not up to the task. It might work in an amplifier with lower capacitor values like those built in the 1940's. Today that value has gone from 6 ~ 8 uF  up to 47 uF.  If you rectifier is not new, and one day it just arcs it means it is getting ready to fail.

Steve

Hey Radiofrequency:

Will, Lon and them have a huge thread on rectifiers in the MKIV. When I had one I used old US Made 5Z3's through an adapter. I never had arcing like you describe with those. That did happen to me with a Valve Art in my Zen; it blew the fuse.