After giving up on using my amp with 300B, I put the 6B4G back in and I noticed one side was somewhat weaker than the other. I figured it was one of the tubes not properly seated in the socket, usually it's the Russian driver tube because the pins are slightly narrower. I did my usual wiggling and it settled in place, then went out again. I went to wiggle the power tubes after and I noticed that one tube was much cooler than the rest. I used my new handy dandy IR thermometer that I've been using on everything, and are being used to take peoples' temps too in the age of Covid-19, and sure enough one tube measured 150F or so internally where its mate measured 250F. I checked the other pair and it was more like 220/230, so a better match. I also swapped the cooler tube with the hot one to see if it was something other than the tube but the cool tube stayed cool. And cool is relative, I wouldn't want to grab either tube.
Does this mean that the one cool tube is drawing less current and generating less heat and hence the other gets more? I know this isn't a direct measurement, but can I make this assumption? And how would I measure individual current with a shared cathode? Can I just measure with a single tube and then swap?
What got me started on using the 300B was that I thought I was going to need a new pair soon after one of the filaments crapped out a month or two ago, and I wanted to try something other than the Sovtek 6B4G. I had a spare that I used but it likely didn't match. I may be in that situation anyway.
It sounds as good as ever at the moment, when the driver isn't seated it sounds distorted since one tube isn't getting voltage on the grid and it sits at ground.
Does this mean that the one cool tube is drawing less current and generating less heat and hence the other gets more? I know this isn't a direct measurement, but can I make this assumption? And how would I measure individual current with a shared cathode? Can I just measure with a single tube and then swap?
What got me started on using the 300B was that I thought I was going to need a new pair soon after one of the filaments crapped out a month or two ago, and I wanted to try something other than the Sovtek 6B4G. I had a spare that I used but it likely didn't match. I may be in that situation anyway.
It sounds as good as ever at the moment, when the driver isn't seated it sounds distorted since one tube isn't getting voltage on the grid and it sits at ground.
Last edited: