Your Lores are mighty efficient so I don't see the KT-120s necessary from a power perspective, more a case of how they affect the sonics at low output levels.
Mikirob - Are you looking for a sound quality or more power than a 6550/KT88 or KT90? I ask because most people think they will get more power by dropping a KT120 in place of a KT88. I asked that question because my thoughts were without having higher plate Voltage and Current you won't get any power.
That being said with the specs of the KT120 you should be able to drive it harder than a KT88 before arcing over. It is supposed to be one 'tough' tube. Personally I haven't tried the KT120 yet but am looking to upgrade my Octave V70SE to a V110 (made for both 6550/KT88 and KT120's). Plate voltage on the V70SE is 540V and the V110 is 540V for 6550/KT88 mode and 620V in KT120 mode.
Hi Mikirob -- I am using the KT120's in both a PL Dialogue 4 and a Dialogue 7. To my ears, in my system, they are fantastic. They are better than the stock tubes in every way. They're resolving, dynamic, and just a little sweet. To warm things up, I am also using Mullard CV4003's in both amps. The combination is terrific.
I say go for it.
I'm using the KT-120's in the Prologue Premium Integrated, they replaced cryo treated Gold Lion KT-88's. The KT-120's have vastly better deep bass and dynamics. Can't listen to the KT-88s for more than 10 minutes before I swap back to the KT-120's. Front tubes are Mullard (Valvo relabel?) 6201's and followers are Siemens E82CC.
Davide256 - Using Valvo 6201's (which are a 12AT7) make no sense because all the small signal tubes are 12AU7 in the PL Prem models. In fact, no PrimaLuna product of any model uses 12AT7/6201.
On the KT120 question, they have a little more "snap" than the Gold Lion KT88. But the difference is small IMHO.
EL34? Different animal. EL34 has a warmer top end and fatter mid-bass. Both are winners and easy to do. Comes down to taste. Have fun kids.
Continuing on quite happy with the KT-120's... with the hope that Tungsol makes a milspec version someday for even better power tube definition. 12AU7's remain banned for bad behavior in the front sockets of my PL Premium Integrated with Siemens E81cc (12AT7)triple mica the current champ and Telefunken 12AU7's in the back sockets.
I have a good amount stock of nos Russian 6p3 ce tubes (I was using at my Leben CS660p power amp with a great success ) I sold my amp and searching a new one either Rogue ST 100 or Primaluna Dialogue Premium power amps which capable to work with these tubes ( I am not sure but read some forums they say so)
Could you please enlighten me that your Primaluna works fine with them or you have some troubles?
Thanks in advance
Ben the KT120 works just fine in the Dialogue Premium Integrated as I have used them in mine with no problem. The KT150 works also. Do a search here on Audiogon as there are a few threads covering the 120 and 150. I see no reason why they wouldn't work in the amp. Also you could email Upscale Audio as they are the importer of PrimaLuna. Hope this helps.