Solid State Preamp to replace tube unit

@jimbones doing some quick checking over AudioAsylum and TubesAsylum to see if others with CJ Premier 12 and/or 6550s had tried others such as some of the better KT88s.  Also, located some comments indicating the Premier 12s are 650v at the plate. There is some mention, not a lot, but possibility of running good KT88s in place of 6550s maybe in your Premier 12s, worth checking more to see its a candidate. Seems the older discussions of running the Sventlana 6550s, led to others jumping over to KT88s.  But again, you may need to find multiple sources there to know for sure that its safe in your amps.

On a related note, I helped a friend and we upgraded his older Jolida amp, it use to run 6550s, and a few local friends and I suggested to the try the latest PSVane KT88 TII MKII tube in it. The result has been quite pleasing, less of a glassy modern sound, and more of a lush body/warmth to the amp now. Can be nice if that's what you like. Find a replutable tube reseller of KT88s if you try it.   Note: I run TS KT120s in my own QS Monoblock tube amps, and while I like the KT120 too vs. KT150s, if my amps had lower plate voltage, I'd be running really good KT88s as an alternate.  Long story, I cannot, i have the big amps with extra larger transformers and big plate voltage, will burn them up prematurely.   In your case, though - might be worth a nice try, and worth checking with peer P12 owners, and maybe CJ would advise you on this, worth asking. There are some big fans out here who prefer good KT88s over most of the othe TS KT series tubes fwiw.     

@decooney Thank you so much. Yes I have heard others say they used kt88 as well. Some prefer 88's other prefer 6550's.  from what I know I can use the 88's without any problems.

@jimbones that’s great, on a different path and price point - my local 55-year-in-business audio dealer has retired clients with upcoming birthdays and Christmas presents due -or- goals for their "bucket list" buys. He has ordered quad sets of E.A.T. KT88s. While they are quite pricey, if you want to splurge, I gather from people who purchased them, they were quite pleased. One other possible way to help squelch your TS KT120 desires, these might fill in nicely as another option. . I’ve never tried them but I might if my amps could run KT88s like yours can!

MFG and specs found here by European Audio Team

https://www.europeanaudioteam.com/en/eat-kt88-diamond-valve-wp000023.html

@decooney im sure they are pricey, but HOW PRICEY ARE THEY LOL!!

I have a buddy with lots of spare kt88 to loan me to try. They are EH 88's so they are not the best but should give me an idea of the change in sound I would get.

Back in the day I used to run push pull amps, can't believe anyone likes 6550's, all balls, no subtlety in my amps and setups, much preferred EL 34 or lower powered KT family.