My Martamp Goldstar has developed a problem where after its been on for 30 minutes, it starts to get farty, and the clean is terrible (not that its great, but it used to sound 10x better), especially with the gain and master low, better with the master high. I've swapped single pre and the single EL34 power tube recently, after this started a couple of months ago, and it's still recurring.
Before I take a trip to Martin's does someone have a known good single EL34 which I can give it another test, and can post it to me.
