Smell emanating from prize 130 head

I realize tubes and knowing when to replace them is an art, and have read at this forum that a weak AX tube can cause a meltdown...hence this question:
When cranking, or not even cranking, an early 130 head, I can detect a slight, vague electric smell. All the tubes heat up fine, glow or what have you. It is recently picked up online, and one GT EL34 shows a darkened spot an inch and one half from top. It was sold as recently capped, and sold due to 'retiring from music reasons', which I have no reason to doubt as the seller was unloading personal guitars as well....Not accustomed to smelling this smell...ew-ew that smell! Just looking for a little preventive advice lest Fry-day comes early. Thanks

Is is a adjustable bias version? I assume so by your description. You should check the amp for bias and set it a little on the cool side for prevention. In the area of 21-23mA PER TUBE would be a good place. This will give you a little breathing room. Also, my personal opinion is to trash those GT's and get something else. A new, heavy duty 12ax7 would be a good choice as well. What brand is in it now? With 700v on the plates, there isn't much room for error and that old crap of measuring at point Y only give you the total idle current for TWO tubes so each individual should be measured.