Power Tube shootout 34,6550,88,120,150

just for all practical purposes, l lets leave out the 66,77.
OK, so now, lets imagine we are testing the 5 power tubes listed about witha  pure neutral colorless amp (just for all things being equal, pre tubes all equal, pure colorless) We are comparing these tubes based on each tubes ~~Unique ~~Individual~~ Charatcer , regardless of lab make. New production only, as NOS are not found in any quantities , nor  at reasonable price points. 
I would say the most important  quality to be discussed is midrange. 
For bass, its quite simple to add a  sub amp/woofer,,and highs,,well maybe a  new high tech Neo Beryllium  woill solve that issue.
Although it is true we need to add footnotes on bass/high fq response.
Most importnatly, is how does each tube  resolve 
1) Voice
2) separation of instruments
3) purity of midrange fq resolution
4) low mids/upper mids response
5) openess/sound stage, = low  distortion at higher levels of complex music, say a  full orchestra.
Please add  other characteristics which should be brought into the comparison.
Many of you have years , decades of experience with each power tube in many dif famous power amps, , your imput will be greatly appreciated by all of us newbies  in this grey area of which  power tube suits our needs best  concerning the music we listen to.
Based on my very limited experience with power tubes, so far I have found the 88 to be my ideal tube,,however,,,seems i may have overlooked the ~~6550~~, based ona  short YT vid, of some chinese lute/female voice,,shootout 88 VS 6550,,2 minute vid,,I may have to change my opinion of recent posting ** The KT88 is the best and finest power tube ever made**,,That opinion , may have to be adjusted, to say *2d best*, as i await a  purchase and testing of the 6550, in 2 weeks time. 
My hunch based ona  2 minute compressed  YT upload then further compressed to my comp and $10 comp speakers,, i surmise it is the 6550 which is my ideal power tube. 
Which would make the 6550, IMHO the finest power tube ever designed.
I am hearing things i heard on my JOR with  the famous EI KT90's. = life like vocals, ,,but with the added bonus of tingling, sparkly highs. 
As I say I could be wrong,,but my hunch and intution says i am spot on.
here is the 2 minute clip  on which i base my daring  ~hunch~~.
The 6550 and 88 look very close in construction,,but that might be where it ends,,looks is one thing, performance can be quite another.
Take the 12AX7,, Not any 2 sound  alike,, all have shades of dif voicing.
(I'm a solid fan of Tele, and no others)
I had assumed a  power tube is a  ,,,power tube,,= we are talking power , less about nuances. 
Could not be more wrong.
Although I hear the  tele AX as set apart from all other AX's...in power tubes,,the voicing is perhaps even greater than in pre tubes..where as pre tubes adds a  nuance here, alittle there,,, power tubes vary significantly from each others voicing,,but wait,,that could be wrong,,as i recall, the 90, was very close in voicing as the 88, the 88 offered more openess. 
I sold off my 9-0's, so can not follow up on that shootout.
in fact to be fair to the 150,,i heard this magnificent  constructed tube, with the old Jadis caps, and the 88's with the new M caps... so all things were not equal.. However,,I have the hunch,,the 150's would still retain that ~~blob like, mushed meal mids/rolled off high mids~~ with the new M caps. This is what i am getting at.
We need to bring up our experiences of the fundamental character of the power tube, regardless of quality caps,  quality of amp.
Almsot like trying to hear the power tube itself apart from the components involved. 
The EL34 I hear as a  bit weak, limp vs the 88. So I give more pointsb to the 88. 
The 90, as i say,,was very nice,,but not as full, rich, open as the 88.
again 88 remains as champ,,I have not herad the 120,,but based on my experience, rather limited of the 150,,I'd guessing the 2 are cousins, and thus , lacks the mid clarity i am looking for. The 150 packs low bass,, makes a  great tube fora  bass guirat amp,,not for rich mid range which is required for   clasical,  human voice, jazz.
Bigger is not alays better, and in this case very ture.
Once the 6550's arrive, i will quickly upload a  YT vid,, which will give me further substance , evidence to my hunches. 
Here is the shottout twix the very popular 88 and the rather not mentioned as often the 6550
**all power tubes have their respectful qualities~~ I ain't buying, 
WE are searching for ~~The best of the best~~ in power tubes,, Only 1 tube can be left standing at this shootout, No survivors. Only 1 tube has the fastest gun in this power tube shootout. 
There is no topic anywhere on the Inet where you can see a  fair , honest, and based on bonifide experience, ofa  shootout twix these long standing popular power tubes. 
I am looking for 1 gun standing alive in this wild west town. 
One power tube will be  given the  crown as ~~King of all Power Tubes~~
My biased vote is already in, all money riding on  The 6550.,,as best gun in the west. 


Member DAK808’s response in that DIY thread is notable. He correctly points out higher current/plate voltages and larger transformers typically required and used by amp designers to run larger KT150 tubes (properly).

Also, i.e, noting the newer "MKII" versions of the Jadis JA80 amp is optimized to run the larger KT150 tubes http://www.jadis-electronics.com/en/ja80-mkii-21.php

Quote (DAK808) @DIY:
"...a tube has certain minimum requirements to do its job which is to amplify the signal put on its grid. The voltage and current requirements for the tube is supplied by the power transformer. The larger tubes require more current and voltage than the lower output tubes"...
My tech guy down here Randy Cohen, mentioned the KT150's need to be perfectly matched, so he can raise the plate current so the tube can work as it was designed to perform,,at higher current,,but for some reason he had issues with jadis'  biasing screw,,1 for each row of 3 tubes,,,Mentioned the tubes are not  running at **optimal** conditions..was afraid to raise the current and damage trans.. Mine is Mark 2, early 2000 production,,I think.
anyway,, at the very least i can get some idea of the 150's voicing on mid range,,my critical area for CM..= not what i am looking for,,,
I am looking at several listinsg for 6550's on ebay,,,Honestly the construction looks identical to 88.
Seems as i  recall, the 6550 is a shorter tube vs the KT88, other than that, identiacl construction.

The sound does change notably with +/- bias on my amps running KT150s.  I can swing 20ma either way. If I back it down, the tone changes to EL34 type sound and the soundstage recesses back. If I raise 15-20 ma, the midrange comes out and forward, and the sound stage comes forward too. 

My amps have notably larger transformers and close to 2x the plate voltage to it's smaller self that runs EL34s.  The downside is I cannot run smaller tubes in mine, it will burn them out prematurely, so KT120s or KT150s it is!  They don't sound right until they burn in 100+hrs.  I now truly enjoy the the KT150 output tube sound WHEN mated with proper triode small signal/ driver tubes and proper coupling caps in the amplifiers. Transforms into a very pleasant result. Powerful yet smooth and musical, and with moderate bias, tubes and transformers are mildly warm, not hot at all.   
I just do not think i could be happy with 150;'s, The midrange was too forward, The 120's also may bea  tad too forward in midrange. 
hard to say,, Considering Jadis installed Svetlana 6550's, I have gone full circle, 90's,, 150,s 88's ,, back to Svetlana 6550's,. 
The Gold Lion 88's I found good, but no cigar vs the Svetlana 6550, The design of the 88 vs 6550 are nearly identical, they are more like brothers than cousins. 
What I perfered about the 6550s over the KT90;s , 88's, (tried chinese 88's and Gold lion 88's, EH90's) was the midrange was more quiet, , can;'t say anemic, more recessed lets say, not as forward. We are talking~~ nuances~~ , just shades of different voicing. 
But considering I can only stay with one tube, I had to pick a  tube ideal for my classical music.  It would be hard to walk in a listening session and say which is the 90, the 88, the 6550. 
Now with all my recent mods, it would be interesting to have the Gold lions, EHKT90's back in  a shootout. 
So what it  would come down to is this. What exactly is the voicing one desires in a  specific set up?
That is to say, my goal is ice cold, , = the less warm, the better. 
And I need the human voice as life like as possible.
As I say, all 3 may offer these characteristics. , and it comes down to ~~shades,of differences~~ even miniscle. 
At least taht is my assumption at this point. 
It would great to have both competitive tubes back as a  shootout. But that can not be. I've made my final decision. 
Meaning one can not go wrong with any of these 3 excellent power tubes. 
The 120's, I have no idea how they would respond in a cayin amp/PL amp, both offer more flexibility vs the Jadis Defy7, which really wants to have the 6550 in its socket. 
My guess is the 120's voicing in  certain mid fq's, might be a bit too forward for <,My>> preference. 
After i get my jadis DPL back with all new caps, I will see how the system responds..  The new navships silvercopper speaker cables have slightly  cut back some of the upper mid fq;s, = cut some of the warmth,, which  others might hear as **less beefy**, might even say more anemic with the silver vs Home Depot's all copper wire. 
This could go either way, more super lean with navships silver copper vs more warm with copper. 
I perfer the silvercopper voicing. as now the bass, highs are balnaced perfectly with all mid fq's. 
Thus one notes the sound stage takes on more  separation, each instrument is more focused. 
All my mods together have contributed to this distinct voicing,, which i bet the 6550 is the tube best fit to compliment all the upgrades installed. 
That is each part has to compliment the whole. Its a delicate balance, and so I went for the 6550, pre many mods, but would bet ina  shootout GL88 vs EH90, SV6550, I'd keep what I have. 
Svetlana 6550 is IMHO the best of the 3 power tubes for voicing a  balanced fq range, = taming the mid's to blend perfectly with highs, lows, thus the music is <<miniuetly/minisclue>>more natural, clean. 
Others may havea system where the 90 works for the perference and 88 for another audiophile's ideal voicing. 
who's to say....