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Old 11th April 2013, 01:41 AM   #1
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Default KT88 shootout vintage vs new vs 90

There has been talk lately about the Genelex reissue KT88 and its reliability and the reliability of New Sensor.Let me start out by saying,i'm not a tube dealer so the interest I have in posting this is in the interest of fairness. We have to look at tube manufacturers as a very specialized market and count our blessings we still have them...Imagine what would happen to all the MAC,Citation,Grommes,Eico,Fisher,Dynaco,Scott,and the list goes on,if it weren't for these handful of tube manufacturers.
Now comes the test...These are few of my KT88s,6550s and KT90s,and they all are very close to NOS...Some of the Genelex Labels are getting a little gritty ,but thats from humidity.
To be fair I did use one quad of GECs and two quads of genelex,all being British made so I could get a more objective analysis. I then used two quads of 6550 Tung Sol black plates,one quad of reissue genelex,a quad of JAN GE 6550s,and a a quad of EI made second generation KT90s
I used 4 amps and two sets of speakers for this test...The amps were a HK citation 2 all rebuilt with Jim McShane upgrade kits and the other is a Vintage Mc275 rebuilt with McShane Kits,a pair of Mcshaned Heath W6ms,and a pair dynaco MK3s I restored to stock with k40 pio caps...It does make spec but I will do an upgrade later.
The Speakers are the Martin Logan CLX full range ESLs and a Pair of Newform Research ribbons.
First I listened to the 2 quads of British Gens and the quad of GEC.These all had nice detail and made great power and they like to be run hard..They had accuracy and control but what they lack was the sound of a live performance and that rich layered texture we have come to love about tubes. The longer they were on and if you were just listening unconsciously,they actually had more of the aforementioned qualities.
Then we come to the reissues...I have had this quad since 2007 and I am very pleased with them..The longer these tubes are on,the more in focus they become and depth increases dramatically. These tubes have an aliveness that is pretty amazing and they pull you into the music.Detail,accuracy, and bass a plenty.
Now comes the 6550 TS black plates...Those are my honeys.They have an aura about them that says,yeah baby yeah! They do everything I want and they are elegant and graceful in the way they present the music..Picture being with your favorite sex symbol and her identical twin at your beckon call on a tropical island in the south pacific.That's these tubes..
We then go to the JAN Straight bottle GEs.They are very muscular,have amazing mids and highs and well controlled music throughout.Again,killer tube and loves to be warmed up and it gives you that pull you in feeling.
It has A lot of the Gen reissue character and they both sound alive.
Last comes the EI KT90s.This is the Tungsol 6550 on steroids..They are incredible after two hours on time and they do everything perfect..I would have a hard time choosing a winner but,I would say its a toss-up as the kt90 and TS 6550 each have their own strengths.
Most of the tests were done on the W6MS and the Citation 2 and then the Mc275.The original UK Gens were the only on that lacked life for the first 3 hours...While they had good detail,they fail to excite but some how,they did help the stock MK3s as did the kt90s because they seem to help the poor spec numbers of a stock mk3.
Bottom line,the reissue genelex are a bargain and they do a bang up job
in the Citation 2,W6s,and Mc275.Very musical and silky without the dry analytical presentation of their vintage cousins.The three quads of Brit made Gens all sounded different from 5k up.I will be testing more kinds of KT88s this week..I have been scaling down my collection of stuff.
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Last edited by michaelsamra; 9th June 2013 at 08:47 AM.
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Old 11th April 2013, 02:09 AM   #2
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Nice to know the reissues are doing well. Is it true that the newer Kt66's & Kt88's are not actually Kinkless tetrodes?
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Old 11th April 2013, 02:24 AM   #3
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Mikey,

An important test to try, if you have the time, is a set of Saratov made KT90s. McShane said the early production had poor sound staging, but current runs have improved substantially. With EI gone, a source of good KT90s is highly desirable. EI KT90s, type II or early type III, are the best tube in a "Deuce". It would be nice if the New Sensor made variant can pass muster.
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Old 11th April 2013, 03:32 AM   #4
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Thanks Eli
My friend loves his EH Kt90s..I will tell you tho,the KT90s remind me of a giant EL84..They even look like an EL84 and they are so linear and the power and distortion numbers will make any correct running KT88 amp cut its distortion in half and up the power by 10 to 15%.
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Old 11th April 2013, 03:43 AM   #5
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That Kinkless tetrode thing is a gimmick...They have identical spec and data to a 6550.It was a selling point to try and point out a major difference from the 6550 but on sweep thru an ultra high bandwidth cit 2,I have NEVER seen any difference in the response curve on my spectrum analyzer at one watt,or at half power...I didn't do a full power sweep but I can't see where that would make a difference.
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Old 11th April 2013, 04:20 AM   #6
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Quote:
Originally Posted by michaelsamra View Post
Thanks Eli
My friend loves his EH Kt90s..I will tell you tho,the KT90s remind me of a giant EL84..They even look like an EL84 and they are so linear and the power and distortion numbers will make any correct running KT88 amp cut its distortion in half and up the power by 10 to 15%.
The EI KT90 type IIIs I have for use in my "Deuce" sure do look like 6BQ5s on a lot of steroids. There's no complaining, whatsoever, about the sound they produce. So, looks be damned!
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Old 11th April 2013, 08:33 AM   #7
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Originally Posted by Eli Duttman View Post
The EI KT90 type IIIs I have for use in my "Deuce" sure do look like 6BQ5s on a lot of steroids. There's no complaining, whatsoever, about the sound they produce. So, looks be damned!
I love the looks of the KT90s and the EL84 is one of my favorite tubes..No complaints here.
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Old 11th April 2013, 09:13 AM   #8
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Quote:
Originally Posted by michaelsamra View Post
That Kinkless tetrode thing is a gimmick...They have identical spec and data to a 6550.It was a selling point to try and point out a major difference from the 6550 but on sweep thru an ultra high bandwidth cit 2,I have NEVER seen any difference in the response curve on my spectrum analyzer at one watt,or at half power...I didn't do a full power sweep but I can't see where that would make a difference.
The beam or kinkless tetrode was developed to circumvent the Philips patent on the pentode, nothing to do with marketing.
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Old 11th April 2013, 09:35 AM   #9
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Building on preliminary British work, RCA introduced the 1st commercial beam power tetrode, the (now venerable) 6L6. Talk about a success story, the 6L6 has been continuously in production, someplace, since the day it was introduced towards the end of the 1930s. NO other amplifying device comes close to matching that production record.

BTW, beam power tetrodes do exhibit a bit of a kink, which is of no practical importance. That part of the curves never gets published. So, Mike is not incorrect is stating "marketing gimmick". However, the "fudge" is, indeed, miniscule.
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Old 11th April 2013, 09:42 AM   #10
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Originally Posted by Eli Duttman View Post
Building on preliminary British work, RCA introduced the 1st commercial beam power tetrode, the (now venerable) 6L6. Talk about a success story, the 6L6 has been continuously in production, someplace, since the day it was introduced towards the end of the 1930s. NO other amplifying device comes close to matching that production record.

BTW, beam power tetrodes do exhibit a bit of a kink, which is of no practical importance. That part of the curves never gets published. So, Mike is not incorrect is stating "marketing gimmick". However, the "fudge" is, indeed, miniscule.
Beam power tetrodes are "kinkless" compared with normal tetrodes not with pentodes. I don't understand what you are referring to with the word "fudge". (It's "minuscule", by the way).
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