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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
imintohifi
22 posts
 

Lots of good replies here. I moved on to KT120's from KT88's in my Atlas Magnum with great results. I'd guess a lot depends on your speakers, but the impression of more bass, yet good tonal balance is definitely consistent with my experience.  I've also experienced "flabby" bass associated with older tube amp designs, which is why I got rid of Klipsch Cornwalls and moved on to Quad ESL57's, which don't have the problem of voice coil momentum high damping factor's meant to control. After some experimentation I found the online rec of the Atlas as an excellent match for the weird impedence load of the Quads to be reliable. The KT-88's it came with still had me wishing for more bass, however, despite the excellent midrange. Swapping them out for the KT120's gave me the best of both worlds, and I haven't looked back in the 5+ years since.

wspohn's avatar
wspohn
622 posts
 

I find that I prefer the KT 88s to the 6550s on my CJ premier 11a.

lewm
13,764 posts
 

Imintohifi, you make a good point. ESLs are insensitive to damping factor because they don’t generate “back EMF”, which is a reference to the voltage that is produced by motion of the voice coil with respect to the magnets, in electromagnetic woofers. (Since there is no voice coil and no magnet). Unfortunately ESLs have a problem producing low bass owing to phase cancellation that can only be ameliorated by increasing the size of the panel.

helomech
1,850 posts
 

I have a Cronus Dark that shipped from their factory with PS Vane KT-88s. Years ago I owned a CMII with the KT-120s. Going off memory, this newer version sounds more refined with the KT-88s, but it’s impossible to say whether that’s owed to the tubes or upgraded parts. I think perhaps the bass with these KT-88s is slightly less impactful than it was with the CMII/120s. 

Also, I was told that Rogue has continued shipping their amps with the 88s because the batches of Tung-Sol 120s they have been receiving since the war began have not been able to hold bias consistently. 

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