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    KT120 in old Mk3s

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    zx

    Posts : 194
    Join date : 2011-08-05

    KT120 in old Mk3s

    Post by zx on Sat Aug 13, 2011 8:19 am

    Hi

    Has any one put the KT120 in a stock pr of MK3s?
    Bob Carver There is not a down side.Thanks

    Thanks Bob for the site

    Bob Latino
    Admin

    Posts : 2413
    Join date : 2008-11-26
    Location : Massachusetts

    Re: KT120 in old Mk3s

    Post by Bob Latino on Sat Aug 13, 2011 9:55 am

    Hi zx,

    I don't know have any Dynaco Mark III's here so I can't test the Mark III with the Tung-Sol KT120 output tubes. The design spec of the P-782 power transformer of the Mark III is 410 VAC @ 200 milliamps. Biasing each of the two output tubes @ 55 - 60 milliamps each gives enough overhead (IMHO) to safely use the KT120 output tubes in a Mark III. The amp may run a little warmer but you should be OK. I would bias these tubes the same as a KT88 or a 6550 tube in the Mark III.

    In the two channel VTA ST-120, the power transformer is rated at 410 VAC @ 450 milliamps. (a little more current flow than two Mark III P-782 power transformers). The ST-120 can use (4) KT120 output tubes with no issues. I have been running 4 of these tubes in my own VTA ST-120 for the past year. I know other VTA ST-120 users have been running 4 of the Tung-Sol KT120's in their own amps with no issues.

    My advice is to try these tubes in your Mark III. The amps may run marginally a little warmer but you should be OK.

    Bob

    zx

    Posts : 194
    Join date : 2011-08-05

    Re: KT120 in old Mk3s

    Post by zx on Sat Aug 13, 2011 11:41 am

    How about the sound of the KT120? Now that Some have time on the tube.
    Power wize 20%more output than KT90,KT88,6550?
    Heat wize 10%more?
    If you dont go you wont no,I get that.
    Anyone with the KT120 just what you think No matter what amp
    Thanks for your time


    Thanks Bob for the site

    jhoak

    Posts : 46
    Join date : 2009-10-16
    Age : 58
    Location : Central Florida

    Re: KT120 in old Mk3s

    Post by jhoak on Sat Aug 13, 2011 3:27 pm

    I'm using KT120s in one of Bob's ST-120 amps that I built. I prefer them over the Ruby Tubes KT88s that I started with. BUT... The actual "sonic" difference is very VERY slight. I have swapped them back and forth enough times that I feel like the KT120s are just a little bit "fuller" over all. Hard to describe but for me I can hear the difference

    I really don't think that I'm getting any power output gain by using KT120s at all. From what I understand in order to increase output power with them it would require some changes to the amp design. Something I'm not willing (even if I was able) to do.

    What I DO think the KT120s bring to the party is prolonged tube life. It only makes sense to me. If the output tubes are basically "loafing" at voltages well below rated they "should" last longer. Of course I could be (and probably am) completely wrong about that.

    Try them if you can. They're pretty nice. I like them.

    Bob Latino
    Admin

    Posts : 2413
    Join date : 2008-11-26
    Location : Massachusetts

    Re: KT120 in old Mk3s

    Post by Bob Latino on Sat Aug 13, 2011 6:10 pm

    As Jeff (Jhoak) has said, the KT120 output tubes are designed for higher voltages than KT88 output tubes and, as such, they will probably last longer in an amp that was designed for KT88 output tubes. I also agree with his assesment of the sound of a KT120 vs a KT88. KT120's sound a little "tubier" than a KT88 with more mid-bass content.

    Re: Power output and the KT120 vs KT88. Tests done by my friend in Boston shows me that you get about 8% more power out of an M-125 monoblock using KT120 output tubes vs. KT88 output tubes. This leads me to believe that anyone using a KT120 output tube in a Dynaco Mark III should also get a similar increase in power output. It is doubtful, however, whether you would actually notice any increase in power by the use of a KT120 tube in an amp that was designed for KT88's. When I posted this fact in the M-125 thread someone asked "how this was possible?". My only answer is that KT120 tubes are physically larger with larger plates than KT88's. Maybe because of the larger plates they are able to transfer more electrons from the cathodes to the plates at the same voltage levels? I honestly can't be sure?

    Bob

    zx

    Posts : 194
    Join date : 2011-08-05

    KT90

    Post by zx on Mon Aug 15, 2011 5:53 pm

    Has Anyone had any KT90,i have the EiKT90. It to well work on more B+,800v an it to sounds more tubey than any other tube KT88,KT100,I think KT90 may Sound like the KT120s ,$200 with shipping for a set of tubes....i like the sovtec KT88 midel of the road.The MK3s can sound sweet in pentoiad,i have move a way from UL i find it a little dull in the 3s

    Thanks bob for the site

    mantha3

    Posts : 298
    Join date : 2010-11-10

    Re: KT120 in old Mk3s

    Post by mantha3 on Mon Aug 15, 2011 7:25 pm

    So How about the KT120 tubes... with a GZ33 or GZ37 rectifier... With a pair of 7062 preamp tubes in the phase splitter spots? In a ST120 that is?

    I know the KT120s draw more then KT88s
    I know the GZ37/GZ33 draw more then the GZ34 (I think)
    I know the 7062 draw a bit more the the 12AT7s...


    Bob Latino
    Admin

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    Join date : 2008-11-26
    Location : Massachusetts

    Re: KT120 in old Mk3s

    Post by Bob Latino on Mon Aug 15, 2011 7:47 pm

    Hi Andrew,

    To answer your questions ...

    1. Yes - a KT120 draws a little more current than a KT88 but the KT120 tube works fine (and sounds great) in either the VTA ST-120 or VTA M-125 monoblock.

    2. The GZ33 and the GZ37 rectifiers do draw more current than a GZ34. You CAN use either a GZ33 or a GZ37 rectifier in the VTA ST-120 or the VTA M-125 monoblocks. On the ST-120, the only minor glitch is that both the GZ33 and the GZ37 are tall tubes and they won't fit under a tube cage if you have a tube cage with your ST-120 amp.

    3. A 7062 is a military version of a 12AT7 type tube with just a little less gain. It should work OK in the phase splitter or voltage amplifier positions of the ST-120. Personally, I have never used a 7062 in my own ST-120.

    Bob

    mantha3

    Posts : 298
    Join date : 2010-11-10

    Re: KT120 in old Mk3s

    Post by mantha3 on Mon Aug 15, 2011 8:55 pm

    I thought the 7062 drew a bit more then the 12AT7.... I can't say for sure. marginal I'd guess.

    The 7062 works real well in the high gain VTA in place of a 12AT7. The sound is great. Solid tube as well. If someone wanted to get a tube that would last a long time with little trouble I think this would be a good choice. These 7062 are industrial! The sound is great as well. I'd go with a Mullard 12AT7 center and then a pair of these. I'm running this now. I got a pair of Amperex 7062 on the phase splitter spots.. I like the look of the higher standing 7062s next to the Mullard too... for what looks are worth.

    I was more just wondering if the combination of these tubes would push the limit of Amp draw...

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