New tubes in Rogue M-180 Monoblocks

"08-29-12: Tobes

That seems like very poor longevity/reliability from the KT90 tubes - unless you're running the amps 24/7?"

The amps do get heavy use from morning until evening every day. But I also forgot to mention that the KT-90s were biased at 40 mA as per the manual. When I called Rogue to ask about the KT-120s, they said that their new recommendation was 35 mA, and that's what I've had the KT-120s at since I installed them.

I no longer have a full complement of KT-90s, so I can't do a re-evaluation of them. But I've never felt dissatisfied with the KT-120s.

I have been using the KT-120 tubes in the Rogue M-180 for about 6 months now. They replaced Genelex Golden Lion KT-88 reissue tubes. In my opinion they sound better than the 88's on every level and I have not noticed any drop off in performance to date. I talked to Mark Obrien before I bought them and he thought they made the M-180 perform its best. Most of what I have read FWIW about the KT-90 is that they were a little thin sounding, but i have nop ersonal experience.

Daverz,

Are you sure about the biasing? I was told by both Mark and Nick at Rogue the KT-120 should be biased at 40 mA, just like the KT-90. Are we talking the M-180 monoblocks or the Cronus integrated amp? The Cronus is to be biased at 35 mA, but the M-180 at 40 mA.

Actusreus, I don't remember who I talked to at Rogue. Maybe he thought I was asking about a Cronus. I'll try calling them on Tuesday to get some clarification.

Daverz,
I emailed Mark yesterday to clarify this. He'll probably respond sometime next week since it's a holiday weekend. I'm relatively new to tubes so I'm not sure how to determine correct bias other than knowing when it's quite off; the sound just isn't right. I've searched some of the old threads regarding biasing, but didn't find much general information on the subject applicable to all equipment. Essentially, the advice is to adhere to the manufacturer's instructions, which certainly makes sense.

In the meantime, how do you like the sound at 35 mA? Did you have them biased at 40 mA long enough to make a comparison?