Out of eight KT-120s (four old & four newer) one runs much hotter and lacks the blue inter-electrode glow of the others. The tube has been tried in four different locations (V1 - V4) in my Rogue Atlas. The bias remains about the same as the other, matched quad tubes, so that's not my problem. An IR meter was used to measure a few different spots on the plate and the temps are consistent for seven of the two, matched-quad, sets.
The amp sounds fine, with nothing unusual heard on the channel with the hot tube. Most of the tubes indicate about 280 degrees F. with the one at almost 400F. The lack of glow around the grids is the only other difference from the other KTs. Thanks for any help.
The amp sounds fine, with nothing unusual heard on the channel with the hot tube. Most of the tubes indicate about 280 degrees F. with the one at almost 400F. The lack of glow around the grids is the only other difference from the other KTs. Thanks for any help.
This must be an unusual occurrence because I've been searching for an answer, elsewhere, also, without success. Any random thoughts are appreciated.
Yes, of course you are correct. I'll recheck the bias once again incase I made a glaring mistake (it happens). However, when inserting that KT-120 into the other three positions the bias didn't change more than 3mA from whichever tube had occupied the socket. Again, I'll retest, should I have somehow blanked-out when first checking. OTOH, only a few mA increase over the specified 35mA shouldn't cause that much more heat, I'd think.