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    ST-120 Triode/Pentode Switch

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    jdm

    Posts : 45
    Join date : 2011-04-04

    ST-120 Triode/Pentode Switch

    Post by jdm on Wed Apr 20, 2011 9:30 pm

    ST-120 Amplifer owners, are you using the Triode/Pentode switch? I am a new owner of the amp and wonder how other owners use the switches. Triode reduces the power to 32 watts pre channel, the Pentode mode is full power at 60 watts a side. I have noticed in Triode mode that the main transformer runs 20 degress cooler at lower volumes. I assume cooler extends the life of the amp unless you need the higher power. I am curious how and when others use the different modes and the music quality they hear.

    The ST-120 makes a nice night light also.


    tubes4hifi
    Admin

    Posts : 1261
    Join date : 2008-11-30

    Re: ST-120 Triode/Pentode Switch

    Post by tubes4hifi on Thu Apr 21, 2011 9:40 pm

    triode mode will give a better midrange and slightly forward soundstage, nice vocals and sax
    pentode mode will give better bass and treble and more power, great for rock music

    mantha3

    Posts : 298
    Join date : 2010-11-10

    Re: ST-120 Triode/Pentode Switch

    Post by mantha3 on Thu Apr 21, 2011 9:44 pm

    Pentode X2

    Not that anyone gave it the X1

    mantha3

    Posts : 298
    Join date : 2010-11-10

    Re: ST-120 Triode/Pentode Switch

    Post by mantha3 on Thu Apr 21, 2011 9:46 pm

    My cable TV service has this "soundscapes" channel... Triode was niiiiiccce for this. inststrumental stuff..

    Sorry, what tubes4hifi said X2

    jdm

    Posts : 45
    Join date : 2011-04-04

    Re: ST-120 Triode/Pentode Switch

    Post by jdm on Thu Apr 21, 2011 10:00 pm

    I will listen for the better midrange and slightly forward soundstage in Triode. I noticed the piano is also nice in Triode at lower volume. I like the cooler temps and nice deep soundstage also.

    I am going to try a full set of new Tung-Sol KT-120 and 12AT7W's. What is the biais setting for the KT-120's?[/u][/u] Has manyone measured the output wattage per channel with the ST-120 with the Tung-Sol? I assume the swithes will have a similar effect.

    mantha3

    Posts : 298
    Join date : 2010-11-10

    Re: ST-120 Triode/Pentode Switch

    Post by mantha3 on Fri Apr 22, 2011 8:32 am

    Nice! Report back. I'd be curious to hear what you think of the KT-120 compared to the Gold Lion KT88.

    jdm

    Posts : 45
    Join date : 2011-04-04

    Re: ST-120 Triode/Pentode Switch

    Post by jdm on Fri Apr 22, 2011 11:41 am

    Bob,
    Is the biais .55 for the Tung-Sol KT-120 tubes? Have you measured the output of the ST-120 amp with these tubes?

    Bob Latino
    Admin

    Posts : 2378
    Join date : 2008-11-26
    Location : Massachusetts

    Re: ST-120 Triode/Pentode Switch

    Post by Bob Latino on Fri Apr 22, 2011 12:19 pm

    You "could" go higher on the bias on the KT120 tubes in the ST-120 but after careful listening - I don't find that the KT120's sound much better at higher bias levels. The amp will also run a little warmer if you increase the bias.

    On the M-125 monoblocks, the use of the KT120 output tubes in place of the Gold Lion KT88's gave about an 8 % increase in power with just the tube change. You won't really notice the power increase IMHO.

    The Tung-Sol KT120 tubes, in both the ST-120 and the M-125 monoblocks, sound a little "tubier" than the Gold Lion KT88 tubes with a little more mid-bass content.

    Re: Triode/pentode switches. When you switch to the triode mode from the pentode/ultralinear mode the bias will drop very slightly and the amp will have only about 60% of the power of ultralinear. The amp will run a little cooler. Since you can make the switch from ultralinear to triode with the amp running, many audiophiles favor the ultralinear mode because the amp is louder in ultralinear. To really listen to both moder critically I suggest the following > Listen to a track in pentode ultralinear until the track is over. Make the switch to triode and raise the volume on your preamp up to a point that compensates for the loss of volume in triode. Now play the same track over again and decide which sounds best to you. Understand that your musical tastes, your speakers and other factors may favor one mode over the other.

    Bob

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