KT120 replacement options in a Cronus Magnum II

I have a "new to me" Cronus Magnum II" that came with a shot KT120. Thankfully the am still plays with half the power on the one channel. I'm having no luck finding this tube. Being made in Russia and in high demand I expect the situation to stay lean for some time. Rouge reported that the KT88’s, KT90’s, and KT77's are all compatible. I'm new to the tube amp space and I was hoping to read for a few months before going tube shopping, but I have a situation. 

Has anyone "downgraded" the Magnum II to one of these other tubes?  I'm guessing I should buy a pair so both channels have the same output. Is that right?

What are your thoughts for the best way forward? I spent most of my budget so a pair of KT150's is really not an option. 


You are correct, do not mix tubes of different values in your amp. Also great advice above from the member comparing the specific tubes in the same amp. As far as “ Hot Spots “, are you referring to the Ghetter Flashing ? Watch some Utube videos that show how this happens. You will see how they use inductance to heat the Ghetter material and how it collects the impurities and deposits it on the glass envelope. When a tube fails you will sometimes get a black deposit on the glass. Also if the envelope fails , you will get a grey or white deposit on the envelope. Since you now have a tube amp, take some time to search on the internet. Videos on tube manufacturing are fascinating and reading about how tubes function is very interesting. Having a minimal knowledge of how tubes are made and function has served me well. Also there are many members here that are extremely knowledgeable on this subject. As a kid I built some Dynaco stuff, as well as some SS kits. I found it very rewarding.  Good luck and happy listening. If your 120 purchase doesn’t materialize, PM me and I’ll help you out. Regards , Mike B. 

Don’t mix tubes. Just replace the bad KT120, bias it to spec and you’re good to go.

Tried to make the switch from 120’s to 88’s in my Atlas Magnum III to save some money, but it was so much better with the 120’s in my system that I just had to spend whatever it cost. Fortunately, I found a matched quad of Tung Sols for $400 and was given a single replacement to try to get the most out of the 3 I was left with. 

The world needs more KT120 tubes. They’re musical and authoritative; truly fantastic and hopefully a future-proof, new classic. Good luck with your hunt.