New tubes in Rogue M-180 Monoblocks

I understand the M-180s now ship with the KT-120 power tubes, instead of the KT-80. You can also simply replace the KT-80 with the KT-120 if you already own these amps. I'm curious whether anyone has done it and what their impressions are as far as the difference in sound. Is the over $300 upgrade worth it?
From what I have read about KT-120s in Rogue amps, the KT120s seem to get pretty universal praise.

Note that some Rogue amps need some modification in order to run KT120s. Best to confirm that your Rogue can use these tubes.
You mean the KT-88s or the KT-90. It might help some who want to weigh in the subject.
I too have read only good things about the TS KT-120s but I haven't heard them. There is a lot of praise for some output tubes I found I don't like the sonics of.
Indeed, I meant KT-90, not KT-80. Thanks for the correction, Mechans.

I understand the only "modification" necessary is swapping the top plate in the Cronus amp as the tube holes are not big enough to accommodate the KT-120. I'm not sure whether other Rogue integrated amps would work with this tube. However, the M-180 monoblocks already came with holes big enough so that it's as simple as swapping the tubes. No circuit modifications are needed.
I would double check with Rogue to be extra sure if your current pair M-180 monoblocks can handle the Tung Sol KT-120 tube to be extra sure.
The 120's draw greater heater current then the 90's. You have to make sure that your amp will handle that.
I've been running KT-120s in my M-180s for about 6 months. I'm still using the 12A*7 tubes that the amps shipped with.

Yes, I'd say it's worth it. My comments at the time I did the replacement were:

"They just give you more of everything: more treble, more colors, more drama. As happy as I was with the original sound of the Rogues, I always wanted a bit more texture and warmth on massed strings, and the KT-120s give you that."

Also, from what I've read, the KT-120 is a more robust tube than the KT-90. Depending on usage, I'd expect to have to replace 1-2 KT-90s a year (and a fuse blows when the tube blows). I haven't had a KT-120 blow yet, but only more time will tell.
08-29-12: Daverz
Also, from what I've read, the KT-120 is a more robust tube than the KT-90. Depending on usage, I'd expect to have to replace 1-2 KT-90s a year (and a fuse blows when the tube blows). I haven't had a KT-120 blow yet, but only more time will tell.

That seems like very poor longevity/reliability from the KT90 tubes - unless you're running the amps 24/7?
I bought my ARC amp S/H and I'm still using the same output tubes (SED winged C 6550) after 2 years. ARC tend to run tubes on a pretty rich bias too.
I'll chime in and completely agree with Daverz but add that there seems to be more lower end punch as well with the KT-120 tubes. Highly recommended if your amps can handle them.
Just curious, but I have had a few people tell me that the "sparkle" of the 120 tube seems to wear off a bit after listening to them for a while. Sort of like the new car smell going away after driving your car for a few months. And that the 120s can be a bit harsh. They all went back to 90's after trying them.

I take it most of you are not getting this?

I've not tried any 120's in my demo gear here. I may need to just purchase a few and see how it goes.
I can say that my experience with KT-90s was not good , either. They didn't last long at all and when one blew it took out a resistor, burned a wire, and a fuse, in the amp I was using- not a Rogue. It was enough to keep me away from them more or less permanently. I am curious about the KT-120 and will ask Jadis if I can use it in the DA-60. I have a feeling they won't endorse it.The trannys on a DA 60 are big and probably could manage it but repairs on an older Jadis are Tre Expensive.
"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.

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.
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?
The KT90 was thin/lean sounding compared to the KT120 in my Apollo monoblocks. Had a KT90 blow up after 1 year of light use -- a nasty short; sparks and a smoked resistor. No such issue with KT120 in the same time period -- that said, it's naive to trust the reliability of any Russian power tube. I've only run both at 40ma. Suppose it might be smart to try 35.

There are some good points to the KT90 sound, and some listeners will prefer them, but I significantly prefer the KT120 9.5 days out of 10. The bass response is more powerful -- and it's not subtle. The KT120 is smoother and less harsh. If this sounds good to you, give it a try. If your system is a bit bass-heavy and/or needs extra sparkle up top, then stay away. Suits my current system. I believe all current Rogue amps -- other than the non-Magnum Atlas/Cronus -- can provide the extra heater draw. My dealer's M180s shipped from Rogue with KT120 installed. They've also got a Cronus Magnum with KT120. EVERY time I've asked Rogue "what about using alternate tube type X that draws Y more heater current" -- amp or preamp -- they've responded "yes, it can handle that". Heck, I run 12BH7 in place of 12AU7 in my Apollos, on top of the KT120.
I got a confirmation from Rogue that the KT-120 should be biased at 40 mA in the bigger Rogue amps, not 35 mA.
Thanks for the update, Actusreus. I've already had the 120s biased at 40mA for a couple days now. Perhaps it's my imagination, but the sound is perhaps a bit more present.
I think you took a wrong turn somewhere.......
I have a pair original 1 year old Rouge M-180 which I will try KT120. This amp was delivered from Rouge with KT90.

The issue is that there is a red capacitor seen in the tube hole. Shall I force the KT120 tubes down? I think I can do this, but the cap will be in touch with the tube socket. Are the amps delivered from Rouge with KT120 the same way?

Best NR9
On the issue of the recommended bias for KT120s, in the Stereo 90, the bias meters are off by 5mA (as stated in the manual), so to bias to Rogue's recommended 40mA, the meter should read 35mA.
I'm not sure what's going on with your amp, but Mark was perfectly clear that you should bias the KT-120s at 40 mA in the M-180 monoblocks, and that's what the meter should read. The M-180 manual says nothing about the meter being off, which frankly does not make sense.
As I mentioned, the bias meter on the Stereo 90 reads 5mA low. As is stated in the Stereo 90 manual. I don't know about the other Rogue models. But for the Stereo 90, when the meter reads 35mA, the actual value is 40mA. And an actual value of 40mA is also what I was recommended by Rogue.

Other people with KT120 tubes have recommended a higher bias than this.
I have biased my Rogue Atlas as high as 55. It's heaven but hot and I don't suspect the tubes will last more than a year or so but for me it's totally worth it.

Are these tubes KT120s?
Since I don't know that much about tubes in general, I have to ask: what sonic benefits are to be gained from biasing tubes higher than the recommended setting?