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    New Tungsol KT120 output tube for Dynaco amps - first impressions on 4/16/10

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    • Post n°1

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    Post by Bob Latino Thu Mar 25, 2010 10:44 am

    Kt120 - New Tungsol KT120 output tube for Dynaco amps - first impressions on 4/16/10 KT120composite

    Mike Matthews of New Sensor has just announced that they will soon be carrying the new Tungsol KT120 tube. The tube is not as yet on their web site but a description of the tube sent to me by New Sensor is below. This tube is plug compatible with a KT88 or 6550 tube. They released some dealer prices to me but figure a retail price in the $45 price range per tube. (Retail prices are now posted on the New Sensor web site with a mid May delivery date)

    "March 25, 2010

    In September of 1950 Tung-Sol introduced the 5881, an uprated and industrial version of the 6L6GA with a 23.5 watt plate dissipation, opening the doors to the hi-fi movement of the 1950s. This rugged tube also found a home in the '59 Fender Bassman and servo amplifiers used in B-52 bombers. In 1955 Tung-Sol raised the bar of high fidelity with the introduction of the 35 watt 6550, which could deliver 100 watts with a pair in push-pull configuration. This tube was used in the Dynaco Mark III and Sunn amplifers.

    New Sensor now announces the Tung-Sol KT120, which has a plate dissipation of 60 watts, making it the most powerful tube in the 6550/KT88/KT90 family. A pair of these tubes in push-pull configuration can deliver power levels of 150 or more watts. When used at the parameters found in existing 6550/KT88/KT90 circuits, the Tung-Sol KT120 is impervious to overload, delivering peak power with extreme reliability and long tube life. However, taking advantage of the higher current handling capacity of these tubes, a very unique and super powerful and stable amp can be designed using the Tung-Sol KT-120."

    This tube should work fine in any Dynaco Mark III or VTA ST-120. It could also be used with any Dynaco ST-70 or Mark IV as long as you have an upgraded power transformer.


    Bob

    Specifications for this tube > http://www.newsensor.com/releases/KT120TungSol.pdf

    Curves for this tube > http://www.newsensor.com/releases/KT120TungSol-Curves.pdf


    Last edited by Bob Latino on Tue Nov 27, 2012 6:36 pm; edited 3 times in total
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    • Post n°2

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    Post by Jhoman Thu Mar 25, 2010 8:20 pm

    Bob, what would these do in my ST120? Worth trying?
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    Post by Bob Latino Thu Mar 25, 2010 8:39 pm

    Jhoman wrote:Bob, what would these do in my ST120? Worth trying?

    Hi,

    Yes - when they actually become available they should work well in the ST-120.

    I'm going to order a set for myself and try them in my own ST-120.

    Bob
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    Post by thevic24 Thu Mar 25, 2010 8:45 pm

    Good deal Bob.

    Let me know how they do please.



    -Vic
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    Post by Jhoman Thu Mar 25, 2010 8:57 pm

    thevic24 wrote:Good deal Bob.

    Let me know how they do please.



    -Vic

    Me too!

    Jeff
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    Post by Bob Latino Fri Mar 26, 2010 4:18 pm

    Hi All,

    I just got off the phone with a sales rep at New Sensor. The Tung-Sol KT120 should be in stock sometime during the first week in April. Look for them on their web site in early April.

    Added on 3/27/10 > Now on their web site they are saying a "mid May" delivery date

    Bob
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    Post by kevco Tue Mar 30, 2010 1:45 pm

    I am very excited to actually see development taking place in tube design, this is a very good thing indeed! I have not been 100% satisfied with New Sensor's quality control in the past, but I have found their tubes to be fine sounding although somewhat lacking in reliability. I have not, however, tried any of the "Tungsol" line. Questions I'd like to pose are: Even with an upgraded power transformer, will the ST70 be able to provide enough bias supply voltage to achieve good performance with these? Or are resistor values going to need to be lowered? Also, unless I'm missing something, it's my assumption that these tubes will not produce any more power than 6550's in an ST120 nor will they produce more than about 35 watts per channel in an ST70. The only way that they will produce their claimed output is in a circuit designed specifically for them. Is this correct?
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    • Post n°8

    Kt120 - New Tungsol KT120 output tube for Dynaco amps - first impressions on 4/16/10 Empty KT 120

    Post by baddog1946 Thu Apr 15, 2010 4:47 pm

    Hi Bob:
    After reading the dog's breakfast of opinion on a tube no one has tried yet I am waiting to hear your opinion on it with an open mind.
    If this tube works in an ST-120 and is as good sounding as the KT-88 setup I am using now then I also cheer the return to tube development.
    Are you contemplating some mods if it is good as it should be for the ST-120? I for one am all ears on this one.
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    • Post n°9

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    Post by Bob Latino Thu Apr 15, 2010 5:34 pm

    baddog1946 wrote:Hi Bob:
    After reading the dog's breakfast of opinion on a tube no one has tried yet I am waiting to hear your opinion on it with an open mind.
    If this tube works in an ST-120 and is as good sounding as the KT-88 setup I am using now then I also cheer the return to tube development.
    Are you contemplating some mods if it is good as it should be for the ST-120? I for one am all ears on this one.

    Hi,

    The key thing is that this tube will draw more current than a KT88. The specs for this tube show that each KT120 will draw 1.7 - 1.95 amps per tube heater current. A KT88 draws about 1.5 or 1.6 amps per tube. The PA-060-120 power transformer has two 5 amp 6.3 volt lines. The transformer will probably take the extra current but will probably run a little hotter. I will have to see if it works. I am going to talk to my transformer people and see what they think ?Personally, I feel that an amp would have to be "designed around the tube" to take full advantage of this tube.

    Bob

    Note added on 4/15/10 @ 8:33 PM Eastern > Although these tubes are not available yet to the general public, a matched quad just arrived here at my door from New Sensor. I will try them in my ST-120 tomorrow and report what I find later on Friday ...

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    Post by Bob Latino Fri Apr 16, 2010 12:17 pm

    VTA ST-120 running Tung-Sol KT120 output tubes

    Kt120 - New Tungsol KT120 output tube for Dynaco amps - first impressions on 4/16/10 ST-120withKT120

    At about 5 PM on 4/15/10 the Big Brown Truck dropped off a matched quad of the new Tung-Sol KT120 tubes. I pulled the Genalex Gold Lion KT88's out of my personal ST-120 and dropped the four KT120's in there. They biased up fine with no issues. The bias system on the ST-120 is set up for KT88's. These tubes biased pretty much in the same general area that the Gold Lion KT-88's did. According to the KT120 spec they draw about 1.7 to 1.9 amps heater current per tube. The two 6.3 volt AC lines on the ST-120 are rated at 5 amps each. I let the amp warm up for 15 minutes without playing any music and then set the bias at 55 milliamps per tube. Later the bias was turned up to 65 milliamps per tube and then later to 75 milliamps per tube. IMHO these tubes sounded better as the bias went up. Most of the listening was done at 75 milliamps per tube. The rectifier was a WZ68 Weber Copper Cap and the three 12AT7 driver tubes were a Telefunken 12AT7 in the center position and two Mullard CV4024's in the two outboard postions. Although the ST-120 may be used in either triode or pentode mode, all listening with both sets of tubes was done in the pentode mode.

    NOTE - added on 11/9/10 > After these tubes have broken about 6 months (maybe 500 hours) I listened to them again at various bias settings and now feel biasing these tubes at higher bias settings doesn't really give better sound quality. The ST-120 amp will ALLOW higher bias settings but you WILL shorten tube life and IMHO not gain anything in sound quality with a higher bias setting in the ST-120 amp.

    I listened for about 5 hours with various selections of acoustic jazz, vocals and some classic rock. This system consists of an OPPO BDP-83 Special Edition CD/SACD player, a BAT VK3i preamp, the VTA ST-120 power amp into a pair of Tyler Acoustics Linbrook II speakers.

    Listening impressions ...
     1. In general, the Tung-Sol KT120's seem to have a more "tubey" sound in this amp than the Genalex Gold Lion KT88 tubes that were in there.
     2. The Genalex Gold Lion's have just a little more top end "air" than the Tung-Sol's..
     3. The Tung-Sol's seem to have a more "full" sound with more mid-bass content than the Genalex tubes.
     4. Both tubes seemed pretty much equal in soundstaging in both width and depth.

    Other impressions ....
    These tubes appear to work fine in the ST-120. At no time did the fuse blow or at no time were there any playing abnormalities. The transformers did not appear to get any hotter than when using KT88's in there but I honestly did not make any definitive measurements to verify that impression. With a retail price of about $45 each, they are not cheap but the Gold Lion's are $50 each so they are not cheap either. It is probably not fair to compare brand new tubes (KT120) with tubes that are well broken in (Gold Lion KT88's). These tubes will need more time on them and my impressions could change once they are broken in. I will probably give an update on the Tung-Sol's once these tubes have more time on them.

    Bob


    Last edited by Bob Latino on Thu Mar 16, 2017 8:16 pm; edited 6 times in total
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    Post by wolverine Fri Apr 16, 2010 2:11 pm

    Thanks Bob.....greatly appreciate your time and talents in these listening tests....based on your support for the Gold Lion KT66's I would say you have pretty damn good hearing LOL.
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    Post by Guest Fri Apr 16, 2010 11:31 pm

    .


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    Post by thisisjay Sat Apr 17, 2010 2:02 am

    Given that a pair of KT88's can produce 100w per pair, but the st120 only produces 60w(probably for better sound quality and tube life), it would make sense that the kt120's that can produce 150w will probably end up producing 120w in Bob's design(pure speculation), but it would work out perfect for the next step up to be the ST 240.

    I for one, would buy an amp like that in a heartbeat. The ST 120 has lots of clean power, but an ST 240 would provide the extra juice needed to take large inefficient speakers like Acoustic Research AR9LSI's to absolute concert levels.

    Its great to hear that the KT120's work in the ST 120, but it's like putting KT88's in an ST 70. KT88's work in the ST 70, but only perform to their full potential in the ST 120.


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    Post by Bob Latino Sat Apr 17, 2010 7:29 am

    PeterCapo wrote:Hi Bob,

    Couple of questions for you.

    1) What's the chance of you and/or Roy designing a new amp, maybe monoblocks, from scratch to get maximum possible power from these new tubes? What, something like 150 watts per channel?

    2) Do I recall that you formerly used an Ayre CD player, or am I not remembering that right? Maybe it was an Ayre preamp you had. Have you replaced another player with the Oppo? You must think the Oppo sounds quite good..?

    Thanks.
    Peter

    Hi Peter,

    1. I will Email Roy and ask him what he thinks ... I had the same idea ...

    2. I never had an Ayre CD player or preamp. I was using an older Nakamichi player as a transport into a Bel Canto DAC2 upsampling DAC. The Oppo has more resolution than the older Bel Canto, better bass and has the convenience of an "all in one" player.

    Bob
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    Post by scsidude2 Sat Apr 17, 2010 1:56 pm

    I keep reading about the upgraded power transformer people use to power an ST 120 and was wondering where these transformers are available. Thanks for the review also Bob, look forward to more updates. -Ryan
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    Post by baddog1946 Sat Apr 17, 2010 4:31 pm

    Hi Bob:
    Good thread going on the new KT-120. I am starting a new ST-70-120-? modified amp and am curious to find out what your transformer builder has to say about a KT-120 custom transformer. What mods would you consider for the VTA board or do you think they are good to go as is for the 120?
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    Post by baddog1946 Sat Apr 17, 2010 4:38 pm

    Hi again Bob:
    I'm posting this here as it is related to the new KT-120 amp I want to build. is it possible to get a stainless steel chassis from you or your manufacturer with a few custom holes and a couple others left out? I want to put the amp in a cabinet and some of the locations on the chassis are inconvenient for what I have in mind. Mostly the location of the power switch and the input/ouyput. I also want to do a neater (smaller opening)job on the bias check plugs and go a little smaller than the octal sockets used now.
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    Post by Bob Latino Sat Apr 17, 2010 4:58 pm

    baddog1946 wrote:Hi again Bob:
    I'm posting this here as it is related to the new KT-120 amp I want to build. is it possible to get a stainless steel chassis from you or your manufacturer with a few custom holes and a couple others left out? I want to put the amp in a cabinet and some of the locations on the chassis are inconvenient for what I have in mind. Mostly the location of the power switch and the input/ouyput. I also want to do a neater (smaller opening)job on the bias check plugs and go a little smaller than the octal sockets used now.

    Baddog,

    If you want to build a custom amp you are better off to buy a Hammond chassis and do the cutout holes yourself OR get a sheet of 1/10 inch aluminum and cut your own holes out and then mount the aluminum plate on some wood sides. To have one chassis made up the way you want would be expensive - maybe $200 - $300 ...

    Bob
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    Post by avi.inc Wed Apr 21, 2010 6:36 pm

    Hi Bob

    How about a update on the KT-120's are they growing on you, leaving you flat or still to early to tell.
    I'm sitting here listening to my st-120 love-in it and just can't see it getting that much better but then again.
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    Post by Bob Latino Wed Apr 21, 2010 7:46 pm

    avi.inc wrote:Hi Bob

    How about a update on the KT-120's are they growing on you, leaving you flat or still to early to tell.
    I'm sitting here listening to my st-120 love-in it and just can't see it getting that much better but then again.

    Hi,

    I listen to the KT120's every day in my ST-120. They sound about the same although I haven't really listened critically in about a week - just background music as I am working during the day..

    I want to mention a few things.

    1. The KT120's may not be usable in all KT88/6550 tube based amps. Four tubes biased at 55 milliamps draws 220 milliamps just for the output tubes not including the driver tubes or rectifier tube. By using a solid state rectifier you save heater current because you have no filament to heat on your rectifier. The ST-120's power transformer is rated at 450 milliamps so it has no problem using these tubes.

    2. You won't get any more power out of a KT88/6550 based amp by the use of these tubes. The B+ on the ST-120 with a solid state rectifier is about 515 volts. I have talked to Roy Mottram on this and we figure that you need a B+ of about 630 VDC (or maybe a little higher) and the tubes must be biased in the vicinity of 100 - 120 milliamps each to pull about 120 watts from a pair of these tubes. (UPDATE - 11/27/12 - Testing of the VTA M-125 monoblock amps has shown about an 8% increase in power just by exchanging out the GL KT88 outs for the Tung-Sol KT120. Apparently the Tung-Sol KT120 with its larger plate structure can produce more power with the same B+ and bias setting as a KT88)

    3. The use of these tubes in an older KT88 based amp with a marginal power transformer could take out the power transformer. This is almost the same thing as my warning "Don't use KT88's in an ST-70 with a stock PA-060 power transformer". One of the nice things about using KT66's as opposed to EL34's in an ST-70 is that KT66's draw less current than an EL34. (KT66 > 1.27 amps per tube or 5.08 amps for four - EL34 is 1.5 amps per tube or 6 amps for four). If you use KT66's in your ST-70 you will save about 1 amp of current and your power transformer will undoubtedly run cooler.

    Bob


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    Post by avi.inc Wed Apr 21, 2010 8:59 pm

    Thanks Bob

    I know you run gold lion kt-88 in your st-120 as do I. It will be interesting when you get down to some critical
    listening to see how the KT-120's hold up.
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    Post by Bob Latino Fri Apr 23, 2010 1:38 pm

    Hi All,

    I ran some temperature readings (all in Fahrenheit) on the ST-120 with the KT120 tubes in there. Sorry I don't have a comparison with the KT88 tubes but I may do that at a later date. I just got the "laser" thermometer. You just point it at the place you want to read the temperature and a laser red dot appears on the exact spot and about 5 seconds later the temperature reads out on a digital screen. This laser thermometer is really cool and it's only about $25 on Ebay.

    On a Dynaco ST-70 type amp the left channel is always warmer than the right channel because the rectifier is there on that side. I also forgot to check the temperature of The Weber Copper Cap(??) sorry - but it gets pretty hot. The quad cap gets pretty warm also. The two tube temperatures are one from the plates and one from the stainless steel base. Notice also that the plates on the rear tubes are warmer than the front tubes by about 100 degrees. The front tubes have one side exposed in the front so they dissipate heat better.

    Bob

    Kt120 - New Tungsol KT120 output tube for Dynaco amps - first impressions on 4/16/10 Composite2withtext
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    Post by mwhousto Tue Jun 29, 2010 5:22 am

    I have only been using these tubes in my two stage amp for the last few weeks but are extremely impressed. Of course my amp is not a Dynaco so not sure how long this post will last bu the tubes will live for ever.


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    Post by avi.inc Mon Nov 01, 2010 7:58 pm

    Hi Bob

    I just ordered a set or kt-120's for my st-120. You have been using them for some time now what have you found to be the best bias setting for them.

    Thanks Mike
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    Post by Bob Latino Mon Nov 01, 2010 8:25 pm

    Hi Mike,

     I had originally pushed the Tung-Sol KT120's up to .750 VDC per tube but after these tubes were broken in I did some listening at .550, .650 and .750 VDC per tube. I concluded that there is no real difference in power and/or sound quality if you bias these tubes higher than the recommended .550 VDC (55 milliamps per tube). To me they sounded about the same. My conclusion on these tubes in the ST-120 is to bias them in an ST-120 at .550 VDC per tube like a KT88. The KT120's to my ears sound a little "tubier" than a KT88 with a little more mid-bass content. Not quite as "tubey" as an EL34 though. The nice thing about the KT120 tubes is that they will probably last longer than a KT88 in the ST-120.

    Added 7/31/16 > The recommended bias setting on the VTA ST-120 has been reduced to .500 VDC per each output tube. Listening tests have shown that the amp will sound the same. Tube life will also be extended with a slight reduction in the bias setting.

    Bob


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    Kt120 - New Tungsol KT120 output tube for Dynaco amps - first impressions on 4/16/10 Empty Re: New Tungsol KT120 output tube for Dynaco amps - first impressions on 4/16/10

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