Hi Joseph_68,
Some power tubes glow blue and or purple, some don't, depends on who made them and their design. I have several types of vintage and modern tubes that give off the purple, OOOOOH! so cool looking, and in one of my amps when it is dimed the purple/blue pulsates with what I am playing on the guitar. Think that the blue and purple light show inside an energized power tube is the result of stray energized electrons striking various internal parts besides their intended target, most often the strays smack the inside of the glass bottle, the collision may cause a loss in energy in those electrons and some photons could be given off as energy is lost at a wavelengh that looks blue or purple. I bet that if humans could see in ultra violet and infared as well as the present visual spectrum there would be quite a light show!
Vacuum tubes need a lot of heat to make them work, that is why texts refer to them as "thermionic" vacuum tubes. The orange glow is most often due to heater filaments heating up certain inner parts of the tube to make it work as designed. If the boxlike plate structures, the biggest part inside a tube, are glowing themselves along the sides or all over in areas red to orange then you have an overheating tube.
Think that the best way to get your best answer is to take your amp to a tech and let him look at it. Perhaps there is a resistor in the power section of the amp that was weak and using the old tubes it didn't work as hard as it does now with the new tubes. It could be heating up as a symptom of unusually high resistance due to something wrong with it and stop passing current due to getting overheated as a result of that something wrong with it, resulting in the amp cutting out. Cooling after shutoff could allow it to work again temporarily too. Or there could be a dirty tube socket making poor contact with a pin in one of the tubes as well. Lots of possibilities that can't be nailed down long distance easily.
A qualified tech can use his test equipment on the bench and solve your problem quickly and with more certainty than the average forum member, after all that is what they do for a living. Just as you would take your ride to a mechanic if the engine started to cut out going down the highway 100 miles from home on the way somewhere, so it makes the best sense to take your mesa to a tech who is suitably qualified and used to working on them.
I'm sure that this is not the answer you were hoping for, ($$$) but it should work to your best and quickest if not exactly cheapest benefit! Also provides you with an opportunity to learn about your amp, the more you learn the more empowered you will be as a player.
It is a **** good idea for any tube amp owner to cultivate a positive relationship with a qualified tech. Take care of your tech because someday you definitely will need him to take care of you... 8) Best of luck!
