there are now modern russian and chinese 6550/kt88 variants that deliver substantially more power and better bass response that old school/old design ones - kt90/kt120/kt150
using these tubes has been the whole model progression strategy for audio research tube amps for the last 10-15 years (since the vt series amps) -- objective being to deliver more clarity more solid and controlled bass more linearity, all the while preserving the 'tube magic' higher in the freq spectrum, so to speak
problem is not all amps can run with the higher bias currents and run these tubes properly
so in your case you shd call jeff fischel at cj - ask him specifically if the prem 11a can handle higher power rated tube equivalents mentioned above... i suspect it may not, given its age
btw, the cj tube amps were quite musical sounding but definitely wimpy in the bass department... that’s why some 20 years ago i sold my prem 11a xs, went to arc, and never looked back - just one data point for you...
using these tubes has been the whole model progression strategy for audio research tube amps for the last 10-15 years (since the vt series amps) -- objective being to deliver more clarity more solid and controlled bass more linearity, all the while preserving the 'tube magic' higher in the freq spectrum, so to speak
problem is not all amps can run with the higher bias currents and run these tubes properly
so in your case you shd call jeff fischel at cj - ask him specifically if the prem 11a can handle higher power rated tube equivalents mentioned above... i suspect it may not, given its age
btw, the cj tube amps were quite musical sounding but definitely wimpy in the bass department... that’s why some 20 years ago i sold my prem 11a xs, went to arc, and never looked back - just one data point for you...