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    ST-120 kit no hum no more

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    kevinmi

    Posts : 54
    Join date : 2009-11-17

    ST-120 kit no hum no more

    Post by kevinmi on Fri Dec 04, 2009 4:03 pm

    Since I replaced the 12AT7 tubes with Mullards and replaced the tube rectifier with a Weber Copper cap, my hum at idle is gone. My next upgrade will be replacing the Sovteks with Gold Lion reissue KT88's. Everyone who has listened to my amp is impressed with the sound, and it isn't even fully broken in yet! Thanks Bob, for a wonderful product!

    Bob Latino
    Admin

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

    Re: ST-120 kit no hum no more

    Post by Bob Latino on Fri Dec 04, 2009 5:32 pm

    Hi Kevin,

    Those Mullard 12AT7's, which also have the British designation "CV4024", are the best 12AT7's I have used in my own ST-120. These were made for the British military in the 1980's and are relatively plentiful NOS tubes. Most place sell them for $25 - $30 a tube but there is a fellow on Ebay "bnb_tubes" who sells them in pairs for $39 or $19.50 a tube. This is a great price on a genuine NEW Mullard tube. Sometimes these CV4024 tubes do not say "Mullard" on them but instead say "Valve Electronic" but rest assured they ARE genuine Mullard 12AT7 tubes.

    An interesting effect on all Mullard small signal tubes is that they all exhibit the "Mullard Flash". When you first turn the amp on and the amp is COLD they will flash brightly for a brief second and then light up normally. On a VTA boarded ST-70 ot ST-120 this will be more noticeable on the CENTER 12AT7. This "flash" does not hurt the tube and will not shorten its life. It is just a function of the unique way that Mullard makes their filaments. Interestingly enough, when these tubes are warm they won't flash. If you shut the amp OFF and then on again within a couple of minutes - no flash.

    Bob

    kevinmi

    Posts : 54
    Join date : 2009-11-17

    Re: ST-120 kit no hum no more

    Post by kevinmi on Sat Dec 05, 2009 7:35 am

    Bob,I got my Mullards from bnb tube like you recommended,and bought 3 to replace all the 12AT7's. I like the flash when I turn the amp on!

    antipodean

    Posts : 3
    Join date : 2010-10-04
    Location : Sydney, Australia

    Re: ST-120 kit no hum no more

    Post by antipodean on Mon Jan 23, 2012 5:17 am

    I've just received three Mullards along with two matched pairs of Kt120s ... yep, going all out on the tube front.
    When I plugged it all in an powered up the "flash" spooked me ... I thought I'd toasted the little fellas. But no... and then found this post - thanks again Bob! I'm now somewhat more relaxed that no damage is being done.

    I'm reset the bias and running through some random tracks in our library (We have >700 CD's ripped in FLAC and running through a Squeezebox). Hoping to get to run a critical ear past everything in the upcoming weekend ..

    BTW: Bob, thanks for the ST-120 ... it's a great piece of kit and even works upside down on this side of the planet ;-)

    Anthony

    Bob Latino
    Admin

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

    Re: ST-120 kit no hum no more

    Post by Bob Latino on Mon Jan 23, 2012 7:03 am

    Hi Anthony,

    There are many references online to the "Mullard Flash" ... It is just the way the filament is constructed. I have had three Mullard CV4024's in my own ST-120 now for about 3 years. I play this amp almost every day. They "flash" everytime you turn them on when they are cold. The cold turn on flash does not hurt these tubes at all.

    Bob

    Jhoman

    Posts : 25
    Join date : 2010-01-03
    Age : 56
    Location : Meridian, MS

    Re: ST-120 kit no hum no more

    Post by Jhoman on Fri Jan 27, 2012 5:55 pm

    Bob Latino wrote:Hi Anthony,

    There are many references online to the "Mullard Flash" ... It is just the way the filament is constructed. I have had three Mullard CV4024's in my own ST-120 now for about 3 years. I play this amp almost every day. They "flash" everytime you turn them on when they are cold. The cold turn on flash does not hurt these tubes at all.

    Bob

    I have three Aperex Bugle Boy 12AT7s in my ST120 running KT120s. My Bugle Boys also flash, I like them better than the Mullards, they seem to have a litle more detail to them. Still have my Mullards as a back up.

    antipodean

    Posts : 3
    Join date : 2010-10-04
    Location : Sydney, Australia

    Re: ST-120 kit no hum no more

    Post by antipodean on Fri Jan 27, 2012 7:18 pm

    Hi All,
    I've had the KT120 + Mullard combo running for nearly two weeks and I have to say that I am underwhelmed with the result.
    The mid and higher detail is all there, but what's (now) missing is depth of bass.
    Whilst instrumental bass (such as double-bass, keyboard and electric bass) all still come through, bass-drum beats feel "pulled" almost as if the is a clipping. I've been listening to many tracks that are familiar with the original set of tubes that Bob kindly sent with the ST-120 kit (Sovtek KT-88 + ElectroHarmonix centre) and the bottom end is far "tighter" now to the point of losing musicality.

    Can anyone offer some words of wisdom?

    Thanks,

    Anthony

    Bob Latino
    Admin

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

    Re: ST-120 kit no hum no more

    Post by Bob Latino on Fri Jan 27, 2012 8:07 pm

    Hi Anthony,

    Different types of CD players, preamps, amps, the tubes used in the amps and speakers sometimes DO sound better in certain combinations. Tubes that are a little brighter can sometimes bring out more detail in speakers that may have a more mellow top end response. There is no one "best" combination of the above that will work with "all" music systems. The end user should try out different combinations to figure out what is "best" for his system.

    Re: KT88's vs. KT120 output tubes. KT88's usually have very slightly more output at both EXTREME ends of the frequency spectrum. By this I mean below maybe 35 Hz and above 12 to 15 KHz. Most speakers, however, don't have much output below 35 Hz. Consider also that many of us "older listeners" don't hear much above 12 KHz anyhow. KT120 tubes (IMHO) sound somewhat more like the EL34 tubes used in ST-70 amps. KT120's are excellent tubes in the mid bass and vocal range.

    In the VTA stereo amps the CENTER 12AT7 has a large influence on the sound of the amp. I personally like the Mullard CV4024 (12AT7 equivalent tube) in this position with the associated equipment that I have in my music sysytem - BUT - if you want slightly more "top end response" try a NOS RCA black plate 12AT7.

    If you "tube roll" a little most users can eventually find certain tube combinations that will suit their system.

    Bob

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