so I bought some NOS tubes for my fathers 60th Anniversary Fender Woody Pro Junior. some JAN Philips 5751's from the 80's and some Tesla EL84's, dating back to 1964. matched pair. we put the tubes in, turn on the amp and after one magnificent full sounding chord, the volume drops off by 60%..... I smell burning..... and I immediately look at the tubes to see one of the Tesla's red plating. oh well. they were a cheap eBay buy and thems the breaks. I switch out the Tesla's for the stock JJ's and the amp sounds great again. so I took the Tesla's home and thought to myself that I'd put them in my AC15 and take a photo of the offending tube to show it to the seller. wasn't interested in filing a claim, just more of a heads up. I put the tubes in, turn on the amp..... and they're fine. I start playing and there's nothing wrong! I played for half an hour. no issues. I can't for the life of me work out what's going on??? both Tesla's tubes are looking the same, the volume is consistent and they appear to be fine. how is this possible?