KT120 replacement options in a Cronus Magnum II

Agree, replace all 4 tubes and re-bias when you're changing types. Also agree the Gold Lion KT88's are great tubes. I've rolled them into my Rogue Apollo Darks and I think there's a good argument to be made they're better than the stock KT120. The GL 88's have a sweeter midrange and an overall more refined sound. 

In the past I compared EH KT90 versus KT120 - the KT90 are brighter and leaner. I greatly preferred the KT120, though systems which lean a bit dark (need a lift in air and sparkle) could conceivably benefit from the KT90.

In other amps (VAC amps - not Rogue) I've compared EH KT88 versus GL KT88. Here the EH KT88 are a bit more rock 'n roll; the GL are a bit more refined and smooth. I put the Gold Lions back in, but I really like the EH 88 and keep them around for a change of flavor/pace some day. I don't think you can go wrong with any of the modern Russian KT88, and the Gold Lions are an easy general recommendation. 

That sucks about the KT120 shortage - a lot of tube amp makers have been using that as a "stock" tube in their amps for a while now, and I wonder if the tooling (dating back to 2009 / 10?) is getting worn down :( 

@mulveling I’m with ya man, only have so many spare quads of KT120s and KT150s lying around. If New Sensor does not figure out how to get them out, its only a matter of time before PSVANE and others start producing clones, Read something recently about Mike at NS/Sovtek reaching out to PSVANE regarding this. Maybe another path of getting production out to clients. Will be tracking this.

Unfortunately, I think Psvane DID try to make KT120 several years ago - and it was a complete bust due to failures and general poor reliability. Then their KT120 just quietly disappeared from the market. That doesn’t bode well for them filling in KT120 production.

KT120 had been stock in Rogue amps for many years now. You can run the KT120 in these amps at a higher bias (40 - 45mA, or even 50mA if you’re bold) than KT88 (35mA). In operation, they should be fairly close with more headroom (plate dissipation) on the KT120. For both the Rogue Apollos and VAC 200iQ’s I’ve rolled tubes in, Gold Lion KT88 vs. KT120 is just a matter of preference. KT88’s are more refined, slightly sweeter midrange; KT120 have more fullness and bass presence, overall a very voluptuous and "powerful" sound -- this is why Rogue switched to them (also they suffered through many faulty batches of Electro Harmonix KT88 in the 2000s). But the KT120’s upper mids can be a little rougher and drier in comparison. I didn’t even notice that for the first few years, but over time it wore on me a bit. That’s why I switched to Gold Lion KT88 in the Apollos, which aren’t naturally sweet like the VAC amps.

KT150 is a very different tube; they were safe to run in 200iQs but sounded awful. That’s where I buy the argument that an amp needs to designed *specifically* for that tube. But KT120 vs. KT88? Nah, they’re close enough for many models with adjustable bias and auto bias schemes. Roll and have fun, if you’ve got ’em.

Currently running Mullard KT88 in my 200iQ’s, and these tubes are excellent as well -- they will definitely sound great in the Rogue amps. But the KT120 are really excellent in those VACs. The VAC’s midrange covers for the KT120. I hope production files in again.

And now making tubes for some high-end amp manufacturers, easy to spot, see them at my local audio dealer. Several tubes out now since. Quietly working in the background. Counted 75 different versions and levels of tubes in production now this week. They don’t seem to be slowing down yet.

@decooney - that’s fair! I might give them a shot if and when their new KT120 hits market. I still kinda want to be a tube snob, but my desire for good sounding tubes (that are actually available) far eclipses that. And I have to admit the VAC-selected Shuguang / China 12AX7’s they use in their gear sound DAMN good - some of the finest!