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KT88 vs 6550 vs ? for warm midrange - using Cronos Mag lll

I've been listening to an ST70 with EL34 Tubes & really enjoy the Sound .

Using the Cronos with KT120's  it's a different sound / feel - sounds wonderful but seems either more balance / neutral overall . Maybe more lower end but not as sweet in mid range as the 34's 

34's in the cronos is possible but not really advisable [ too much current into tubes - 1/2 the life span  even with proper biasing ] 

I've been running the amp in Triode mode and seem to prefer sound .  Listening levels are moderate / low  avg 75 db 

I'm good with the kt120's but maybe another tube would bring more mids to the game 

 

* Note - I have changed All the preamp tube to NOS - It has been a significant improvement !-  Telefunken is at center  12au7 , flanked by RCA clear tops , 2 GE ax7 's 

Any suggestions for power tubes is most welcome - Rogue audio is shipping  kt88's in lieu of the 120's [ for yrs due to war etc.] 

what's gained or lost when changing from the 120's ?

 

forgot - Primary Speakers - Dynaudio special 40's , primary source is Vinyl 

 

Thanks  

 

mfm22

Showing 1 response by dogberry

dogberry
812 posts
 

I recently managed to get hold of some Svetlana (St Petersburg) KT-88s from valvesnmore.com. They are at least as good as the Sophia Electric tubes they replaced. But I too, have read good things about NOS winged C 6550 tubes.

I'm using Quad II/forty monoblocks, but I am not sure if they are fixed or auto-bias (looking at a circuit diagram I believe it is fixed bias). Quad have told me the 6550 tubes will work, but "since the amp is designed for KT-88 tubes it may not be optimal." Apart from slightly reduced power output (35W vs 40W) the real issue is bias. Am I right to think that the fixed bias that can cope with any number of KT-88s that might be used is also likely to cope just as well with 6550s?

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