KT120 back to 6550


Seen a ton of threads praising the KT120 over the 6550 or KT88. I get the new tube's durability and design but given that your amp was originally designed around one of the older tubes has anybody gone back.

I recently purchased and ARC Ref 110 that came with a set of KT120s. The output tubes test and match well so they don't seem to be at the end of their life (same for the signal tubes). 

This was a change from a VT100 equipped with 6550s. The VT100 had good midrange but seemed a little lean otherwise. Percussion was fantastic and voices just right. Just deep bass a little thin. The REF 110 definitely fills in the deep bass but seem a little congested in the midrange. Both top and bottom are an improvement.

Both these amps were sandwiched between an LS25Mk1 and a pair of JBL 4430s. Could be a synergy thing, these speakers work very well with high power solid state (Adcom GFA 5802). I've been trying to work up a good tube amp for these but so far I'm not feeling the love.

So the question is could it just be this system would work better with 6550s instead of KT120s?

Thanks
monoogan

Showing 8 responses by daveyf

I believe that if an amp can work well with 6550's and can also accommodate KT120's...then the KT120's would be the superior tube in that amp. However, the big question is whether the amp can actually support KT120's without damage...as most that were designed for 6550's cannot. I went from an amp with 6550's to a mono block with KT150's...very big difference. 
lalitk, I would suggest checking with ARC first before rolling in the KT120's and particularly the KT150's. I would be surprised if they told you that your VT-80 was compatible with these tubes. Best to get ARC's blessing before you damage your amp.
Tommuch, I see that the VT80 can apparently run with KT150’s. What is odd is that the newer VT80SE includes the KT150’s, and so I’m not sure what is the difference between the 80 and the 80 SE??
Lalitk, I believe the KT150 requires a higher draw, as such it can damage the transformer if that is not up to the task. Presumably, the transformer in the VT80 can handle the draw like in the VT80SE?

@runwell  Specs to me do nothing, unless they confirm what i am hearing with my own ears...and even then I give them very minimal credence. 

@kingpin75s  I have heard the same thing as you on several amps, the 6550 sounded better. However, these amps were originally designed to run on 6550's and then modded to work with KT120's. Of the amps that were originally designed to work with KT120's, that is usually the best sounding tube for them. Was your amp originally designed ( circuit wise) to run 6550's?

@runwell  "6550 is better for vocal for sure than KT150"--where do you get that from?? "KT150 might be good at both end but not middle"---Huh???

 

 

 

@runwell   No, my idea is from actual listening experience with my own amps and in my system, or with friends amps who are using KT120’s. What amps are you referring to?