Power Tube Failure

Op , are you referring to one of the four 12AX7’s in your Zesto Andros phono pre ? When a tube looses its seal or cracks the incoming air causes the tube to turn white. I’ve had this happen twice with power tubes without causing any damage. The glass cracked ( I assume from heat and age ) and this causes the tube to fail. Just like when a lightbulb fails. If your phono stage has a fair amount of time I’d just put 4 new tubes in it. I’d also ask Zesto this question for a more accurate answer. I have had power tubes fail and damage my amp and the tube had no visible damage. It was only identified while on a tube tester. You might look up your local short wave / ham radio club for help with testing. My friend is a musician and has one of the modern “ Orange “ testers and I’ve borrowed that with good results. Best Wishes , Mike B. 

@buellrider97 

Thanks for the information.

I am only referring to the power tubes. I have one in my PreAmp.  

Yes, the impetus of this question was the loss of a tube in my Phono Preamp, but I am not very concerned with possible damage of low-amp tubes like the 12AX7s.

Also, good to hear about your success with the 'Orange' tester.  I am window-shopping for a tester, but need to better understand the limitations of each. 

Best,

@inagroove 

I only get two answers from my inexpensive 'basic' tester.

I recommend them so you can AT LEAST know something about your used tubes, when something is amiss, and test new ones when they arrive, i.e. are they 'matched' as the seller said they were.

1st, test for shorts. I have found a few over the years, not many, but a few. 

2nd, IF no short, test for strength on the scale which has reference numbers:

BAD (red); ?; Good (green), 

Good: record the number it reaches on the scale after warming up 1 minute, and check if the tubes are very close in numbers, i.e. matched.

A new tube is not 100, it is what it is, i.e. 72, just a number.

I just tested a dozen 5687's for my friend, a pair of new 'matched'; a pair of old ones he pulled when he initially purchased the mono-blocks used (and didn't have a tester) and 8 'no brand' used tubes the seller sent along as spares with the sale.

Turns out, the most closely matched pair was the pair he had initially pulled (shame he didn't have a tester, like I say, he was blind).

no shorts, they ranged from 68 to 74, several very close pairs could be made, and the new pair were 70 and 72.

what do the numbers mean? hell if I know, they are well up into the green!!!

///////////////////////////////////////// 

If you want to know more that that, you need a better tester. 

btw, my wife bought mine used in 1983, and I've had the ability to at least get those answers for all my tubes for 43 years.

It has never been calibrated, I don't care, a short will show up, and the color green, and the uncalibrated numbers are comparative to each other, just like my inexpensive SPL meter is. I can calibrate it, but why bother,

relative comparisons are all I want to know.

may be too late here, but check your voltage. could be spiking at certain times each day.

@elliottbnewcombjr 

Thanks, that makes sense as a place to begin.  Yet I need to admit, with Bad (red);  Good (green) my 'Geeky' side dies just a little bit ;-).

That said, I will try to get an instruction manual with whatever tester I purchase.

Best