KT120 replacement options in a Cronus Magnum II

Budget is a bit of an issue. I understand it may not be ideal, but what is the downside to getting a pair of KT88s and holding the remaining working KT120 for when the next KT120 goes? 

I don't think the tubes are as much tired as the previous owner never heard of biasing them. There was 1 position where the bias was way off! I'll bet that's where the now dead one sat. The amp let's me bias per tube and it was the first thing I did after an initial warm up period and how I discovered I was down 1 tube. Okay, yeah, I did not notice that 1 tube was not glowing. I was just playing the amp quietly and working across the room. My listening room is also my work from home office.

As a data point, the amp sounds absolutely amazing even with only 1 tube on the one channel. Yes, if I drive it hard the one channel starts to deteriorate, but that is not normal for me. My, also new to me, Cerwin Vega E312s are very efficient and I don't need to push the amp to more than fill my room. 

I'm looking forward to rolling the other tubes, but I need to let the buying settle a bit first. In the past month I got the Cronus Magnum II, Denon DN-300Z, and E312's. My credit card is a bit warm. ;) I was hoping to upgrade my stylus to the AT-VM95SH. I have to weigh the sonic impact of 4 tubes and no stylus upgrade with 2 tubes and a stylus upgrade. 

Great questions. Here are the answers:

I have swamped the tube and the issue follows the tube. I get no current when trying to bias and the tube does not get warm has a burn spot on the its side unlike the "hot spot" of 3 other tubes. 

Rogue Audio said it is okay to operate the amp with the dead tube. It is inserted. I turned it off at first until they advised it was okay.

I finally tracked down a KT120 for sale. I'm now thinking to buy 2 KT120's and get the 3 remaining working tubes tested. Set the weakest aside as a spare. Delivery on a new tubes will be 3 weeks. 🙁 Getting the tubes tested is also not trivial as the nearest shop that I know of is an hour's drive away. I will keep looking closer to home, but I live in rural Ohio.

I like the idea of a full set of KT88s sitting in a drawer. That may be a Christmas present to myself. 

I forgot to ask this clarifying question:

Yes, I was thinking of 2 KT88s. The thought was can I run a KT120 and KT88 on each channel. It sounds like that answer is "No!".  I'm a newbie and not finding good content to figure this out for myself. 

Thank you for the replies!!!

Indeed, I had the resort to eBay and there is only 1 seller shipping from China. I just ordered 2 so I have a spare. I suspect the war is causing import issues. No sign that will be over any time soon. Now I wait 3 weeks.

Avanti1960, did you roll any of the pre-amp tubes? That was my plan come next winter. I saw 1 thread indicating some success. I'll bookmark them for when my wallet recovers.

If this is PcX,Tube New Tung-Sol KT120 (Super 6550/KT88) (partsconnexion.com) they sold out already. I got 2 off ebay and they work great. I have a spare now for the inevitable.