Genelex Gold Lion KT 88 “burn circles”?

Does anyone know why I bought an amplifier with these tubes, only two of them and there are these black circles on the outside glass of the tube. I don’t know if they’re good or bad and does anyone know if I need to have a matching family quad of KT 88 from Gold Lion or can I add another pair to these brown spotted ones? I see two more brown spotted ones from the UK for sale and I wonder if I should get them to match? Not knowing how old the others that I have obtained on my CARY SLI 80 signature amp. It would be an expensive mistake to buy two more of the same tube. If they are supposed to be bought in a quad, and I do not know the age, hours, on the two Gold Lions that came with the amp which are said to be rare?

128x128Ag insider logo xs@2xmoose89

Go test them before you turn on the amp.

make sure it close in reading , if don’t have tester just buy new one .

black or dark round is mean used lot , shiny is new look.

better buy match tubes .



Like a broken record, I keep on saying anyone with tube equipment should buy their own tube tester. 



Shops that sell and repair musician's amplifiers will have tube testers.The dark spots happen when the tubes are used.It doesn't mean they are bad necessarily. Gold Lions are not rare,they can be bought new from any retailer that carries the Genelex brand. I'd be curious why an amp that takes four power tubes was sold with only two tubes included. If two went bad was there a problem with the amp?It may need to be serviced 

Post a photo if you can.  If you use google photos a link works well. Example:  


That's just what some tubes do. I've had 3 pairs of 300B tubes, including $1300/pair Western Electrics, and the glass towards the bottom turned dark on all of them quite quickly with use. 


Are the circles silver/black?  If so it’s perfectly normal.  Some tubes have them on the top, some have ‘em on the sides. It’s all part of Getter , shoot, I can’t remember the exact name. As the tube ages, it will get smaller. That’s one way to know when it’s time to check your tubes and see if you’re getting near needing to replace them.

All the best.

Have a quad of Gold Lion, KT88 in my Cary amp as well - all 4 have that flash spot and it developed over the 1st year of use. Tubes test fine & play great/no worries, have a matched set of RCA clear top 12au7 in my DAC as well with the same flash spots. All good! 

Thanks to all. I acquired the other two to make a quad of the Gold Lion KT88. I wonder why Cary suggests 6550 in the owners manual

I was fortunate to buy as PARTS ONLY EBay purchased. Gambled that the Seller saying “won’t power up” would be a fuse issue. Obtained for $1200. All fuses were bass-Akwards; slow in the quick; quick in the slow, and the one near the plug has one hidden. 

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