Jasper and David, ... other than double secret hearsay comments that have been published here and on another website, I have *NOT* read or heard directly out of ARC's metaphorical mouth that the KT-150s are approved for use in other models, be they current amps or older models. If either of you gents can point me and the others to a direct *OFFICIAL* source, the collective "we" would be grateful.
(@Jasper, you are the official A'gon grammarian, should I say "the us'es" as in "us" plural instead of saying the "collective we"?? I want to come off as an erudite.)
David, ... having said all of that, until and unless ARC blesses the KT-150s for use in the ARC Ref 110, I would be very cautious about dropping in the KT-150s. As an "fyi" the current Ref series amps (i.e., Refs 75, 150, 250 and 750) were designed to run with KT-120s. The KT-120 is a more robust tube and draws considerably more current than its predecessor, the SED 6550 "winged C."
Stated differently, the marginal difference in power draw between the 6550 and the KT-120 is much greater than then the marginal increase in power draw between the KT-120 and the KT-150. Check the web yourself to confirm what I am saying.
Nevertheless, it would not surprise me that ARC, if and when it gets off its royal corporate arse, may ultimately bless the KT-150s for use in the Ref 110. ARC amps are very robust and can take a "lickin' and keep on tickin'" so to say.
In the meantime ... we wait for its royal majesty to get off the can. And as the official A'gon audiophillic (sp?) erudite Wolfman would say, it's time to can it sweet prince. Say goodnight Gracey. LOL :)