It was wicked cool too! Was cranking some tunes and gave it more throttle. Was enjoying the warm glow of the tubes as the left channel 12au7 erupted in internal flame and then... my world went mono.
It had been one of a matched set of Amperex Bugle Boys that I suspect were fake. Bought em on eBay, where the set for sale had ink including the logo. Set that arrived had nothing at on them. Oh well. Live and learn. It was a fun light show though! I’m just glad I got to enjoy seeing it pop.
Replaced them with a matched set of Siemens Halske ECC801Ss. Like these better anyway.