Good 6550/KT88 tubes

The three KT-88 choices are -- Svetlana, Tesla, and Electroharmonix. Svetlana is warm, full and nice. Tesla is also nice, a little brighter on top, little less warm. The Electroharmonix is too new and not much is written about their sound except a few people's comments how they like them. I have some for sale I bought and didn't use cause I switched to a non-KT-88 amp. The EH is being used as stock in the Magnum version of your Rogue 120, however.

Some guy has an ad for EH 6550's and says they are the identical tube to the EH KT88. NOT!
They may look the same, but they are not the same. Although I really didn't get a chance to really listen to the EH KT-88, I did briefly compare it to the EH 6550 and it was definitely better. I, too, did note the how similar they looked, but they are not the same.

If you're sufficiently committed, then get some original Tungsol 6550s. They're noticably superior to the EHs that came with my 88 Magnum. Am using them in conjunction with mullard cv4003/4s.

If you are REALLY commited, get some 'black plate' GEC KT88s from the 1960s.

Since TungSol 6550's are about $600-$900 quad, and GEC's $1200-$2000 quad, Svetlana's KT88's are about the best I have heard, for reliability, and sonics. The ones with the wing C logo, are the ones made by the factory in St. Peterburg. The others labelled Svetlana are made by Reflektor, which makes the tubes sold under the Sovtek banner.If you have the bucks, the vintage tubes, do sound better, and tend to last 3-5 times as long.