6550 vs KT88 vs KT90

EL34's in each amp. I haven't tried 6550's due to my satisfaction at this stage and $$ for yet another dozen of tubes.

Don't need to roll to 6550's,
Your KT88's are in fact none other than,,,yep you guessed it, due to miniscle differences, same as mt Svet 6550's ,
IMHO the Svets6550's.  will shootout all other 88/6550's ever made.
In all categories,,including the most important characteristic, reliability. 
Built like tanks, sings like angels...

I am trying to replace my tubes that originally was KT90's on my Jadis orchestra

East EU tubes are like chinese power tubes, unrelaible, Those KT90EI's that came with the Jadis Orch Refer went bad after 1500 hours. = Junk  and  set the record for screechy harsh sounding. 
They fetch like $100 each now,,lol...
But when new, set the record for life like sound stage/female voice. WOW,, but hard to deal with the  steely highs. , The Svet 6550 has none of these issues. 
Its a tube you can <<relay on>> session after session,,and on and on, for years, = faithful tube. =  Gold winner.

experience on how the new KT88s stack up against the older ones, sonically

NOS Svet 6550(kt88) is ientical to the new production,, so don't pay high prices for *NOS Svet 6550s** Its snakeoil. 
No have not tried EH KT88's, vs Svet 6550's. 
Defy takes 12 tubes = not practical,,I did hear the Gold Lion's,,and found them to be a  bit lower vs the Svet's,. so i returned to vivatubes/12 GL KT88's,  with a  $150 restock generosity fee , and also previous 2 weeks, returned  vivatubes kt90's $100 restock gift fee,,,they said * please sir, go do business elsewhere*,,so I did and rebought for a  <<yep>>a   2nd time,, the Svet 6550's from a  California seller, and that is the end of my long  very expensive search for a  good power tube.

I second the vote for the Svetlana KT 88 vs 6550

It is exactly the same tube,, one can not win out over the other.
If anyone believes they are dif, its snakeoil.

Resurrected an 18 year dead thread, so you can respond (to yourself, repeatedly) about everything sounding the same?       The only thing, "the same" about the Svetlana 6550, that’s been made by Sovtek since SED’s St Petersburg (Winged =C=) plant burned down and took their manufacturing equipment with it (some years after this thread started/ended); is the name that Sovtek/New Sensor/Reflektor acquired.       Not saying it’s a bad tube.            Simply not the same tube.       Just as those that are now manufacturing, Mullard, Tung-Sol, Gold Lion/Genelex, etc, repops.      None of them are the same, or- sound the same, as the original valves.       I have noticed; some of the most reputable tube mongers that used to sell and and extol the virtues of the SED/Winged =C= brand tubes, aren’t selling the Sovtek repops.       Doug’s tubes does list Sovtek’s Svetlana 6550C as, "A great choice for people on a budget."        To each his own, of course!