KT66s in place of KT88 tubes

specifics always rule the day 

generalities only lead one astray...  

poetry to live by 🤣😂

Thanks, all. Time for me to talk to my tube guru.

C.

@jond (and any others in the know) - What sonic improvements do you think I would realize replacing KT-88s with KT-66s? I understand that this will be amp specific but even a generalization would be helpful. I am currently using KT-88s (two per channel) in a pair of DeHavilland 50A mono blocks which will accept KT-88, 6550, 6L6GC, KT-66, and KT-90 output tubes. 

before the advent of modern day russian engineered kt120’s kt150’s and the like, kt88/6550 tubes were the more powerful, most linear strongest pentode/tetrode power tubes, with max plate dissipation about 30-40% higher than earlier el34/kt66 types

as such the kt88 variants offered the greatest linearity when called on to deliver near max power in real world speaker-driving, a level of which is much higher than older weaker el34’s 6l6’s kt66’s as per the above... so what happens in ’typical’ transformer coupled tube amplifiers, using each type of power tubes in pairs, quads, and so on, is that kt88s would provide noticeably better dynamics, more controlled tuneful bass, more extended treble, cleaner transients -- whereas the weaker earlier tubes variants in the same circuit or application (each biased correctly, it is assumed) will sound more mid-range centric, have a more smooth-over, ’romantic’ treble and somewhat slurred transients, have warmer tubbier slower, not-quite-as-deep bass -- this leads some tube amp aficianados to say that the older weaker tubes made for a sweeter sound, where later stronger tubes made for a leaner more solid stateish sound -- all is relative of course...  

as generalities go, for what they are worth, this is what one would expect...

@jjss49 Thanks. I was rather hoping using KT66 tubes in place of KT88 would make my amps sound a little more like the SET amps I used to have. And maybe, from your description (if I look at it in a positive light rather than the reverse) they would. But it would mean changing a number of components inside as they aren't set up to cope with such a swap unaltered.

I shouldn't go making such changes anyway, right now. I'm waiting, and waiting, for MoFi to get some more Quad panels in stock so I can have my 2905 speakers rebuilt, and any dissatisfaction with the sound while I have stand-in speakers in use is not really a reason to make changes that won't be needed when I get my ESLs back in service.