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The Dynaco Tube Audio Forum

Dedicated to the restoration and preservation of all original Dynaco tube audio equipment - Customer support for Tubes4hifi VTA tube amp and preamp kits and all Dynakitparts.com products


    Hum - Right Channel - ST-120

    jimmeq
    jimmeq

    Posts : 53
    Join date : 2017-02-24
    Location : Six Miles West of Jiminy Peak Ski Resort

    Hum - Right Channel - ST-120 Empty Hum - Right Channel - ST-120

    Post by jimmeq on Sun May 31, 2020 6:39 am

    All of a sudden there is a pretty loud hum in the right channel of my ST-120. I swapped L/R Inputs and the hum remains in the right channel. I thought this time I'd ask first. Anyone have thoughts on troubleshooting this further?

    Apologies if this has been discussed but I did a search on 'hum' and received no results. ??
    jimmeq
    jimmeq

    Posts : 53
    Join date : 2017-02-24
    Location : Six Miles West of Jiminy Peak Ski Resort

    Hum - Right Channel - ST-120 Empty Hum - Right Channel - ST-120 - Now Gone

    Post by jimmeq on Sun May 31, 2020 8:52 am

    What a learning experience using a tube amplifier is! With the power off, I re-seated all tubes and the hum is gone. This amp is so quiet, I can't tell if it's on or off just by putting my ear near a speaker. Wow! So, now it's time to re-tension the tube sockets. I'll search but if nothing turns up I'll be asking that question.

    Is tube socket re-tension something that has to be done after a few years of the amp heating and cooling?
    Bob Latino
    Bob Latino
    Admin

    Posts : 2959
    Join date : 2008-11-26
    Location : Massachusetts

    Hum - Right Channel - ST-120 Empty Re: Hum - Right Channel - ST-120

    Post by Bob Latino on Sun May 31, 2020 9:51 am

    jimmeq wrote:What a learning experience using a tube amplifier is! With the power off, I re-seated all tubes and the hum is gone. This amp is so quiet, I can't tell if it's on or off just by putting my ear near a speaker. Wow! So, now it's time to re-tension the tube sockets. I'll search but if nothing turns up I'll be asking that question.

    Is tube socket re-tension something that has to be done after a few years of the amp heating and cooling?

    Hi Jimme,

    Your VTA ST-120 amp is 3 1/2 years old .. Sometimes it is not retensioning that has to be done. It may be just dust that has gotten down into the socket pins and that this dust may have prevented good contact with the tube pins. I would advise trying first a good cleaning of the socket pins with a contact cleaner such as Caig Deoxit. Link below...

    Caig Deoxit contact cleaner

    Bob
    jimmeq
    jimmeq

    Posts : 53
    Join date : 2017-02-24
    Location : Six Miles West of Jiminy Peak Ski Resort

    Hum - Right Channel - ST-120 Empty Re: Hum - Right Channel - ST-120

    Post by jimmeq on Mon Jun 01, 2020 7:36 am

    Thanks! I have some Deoxit on hand. Certainly easier than re-tension. Just for the record, I do dust my ST-120 every week along with all the other components.  Smile  That mentioned, dust does find its way...
    solderblob
    solderblob

    Posts : 86
    Join date : 2018-05-20
    Age : 74
    Location : Placerville, California

    Hum - Right Channel - ST-120 Empty Re: Hum - Right Channel - ST-120

    Post by solderblob on Mon Jun 08, 2020 5:59 pm

    I recently pulled my Mk3s out to give a listen.  One produced a loud hum in the speaker.  A while back I had replaced the blown 5AR4, so I suspected it might be related and put in a brand new 5AR4.  Didn't fix the problem so I re-tensioned and Deoxided the socket.  That fixed the problem.  Then, the other amp did the same thing so I did the socket cleaning on it.  And so far, so good.  Fingers crossed.Hum - Right Channel - ST-120 Mkiiis13

    Mk3s with VTA octal boards.

    dave

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