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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


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    VTA-120 Possible Pentode/Triode Switch Problems

    jimmeq
    jimmeq


    Posts : 60
    Join date : 2017-02-24
    Location : Six Miles West of Jiminy Peak Ski Resort

    VTA-120 Possible Pentode/Triode Switch Problems Empty VTA-120 Possible Pentode/Triode Switch Problems

    Post by jimmeq Tue Oct 25, 2022 5:08 pm

    I was not getting sound from the Right channel, and when I switched into Triode mode the sound came on but very faint and crackly. I turned off the amp.

    Might it be as simple as the Pentode/Triode switch?


    A few years ago the amp had sparks, and subsequently literally partly melted this switch (since replaced), so I'm really paranoid of turning it on again. I will be re examining the solder points...

    Any thoughts?






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    New2Tubez


    Posts : 147
    Join date : 2018-03-20
    Location : NY

    VTA-120 Possible Pentode/Triode Switch Problems Empty Re: VTA-120 Possible Pentode/Triode Switch Problems

    Post by New2Tubez Tue Oct 25, 2022 11:44 pm

    Could be the LM334 on the weak side of the VTA board. When my ST-120 had low volume and "rustling leaves" on one side, it turned out to be this. I followed Bob's suggestions. Do a search on the forum, it's in there.

    I did not have an issue related to the switch. Could that be coincidental?
    jimmeq
    jimmeq


    Posts : 60
    Join date : 2017-02-24
    Location : Six Miles West of Jiminy Peak Ski Resort

    VTA-120 Possible Pentode/Triode Switch Problems Empty Re: VTA-120 Possible Pentode/Triode Switch Problems

    Post by jimmeq Wed Oct 26, 2022 8:04 pm

    Thank you, I'll check that out. A search for LM334 did not turn up any posts with input from Bob. What is the weak side of the board?
    avatar
    New2Tubez


    Posts : 147
    Join date : 2018-03-20
    Location : NY

    VTA-120 Possible Pentode/Triode Switch Problems Empty Re: VTA-120 Possible Pentode/Triode Switch Problems

    Post by New2Tubez Wed Oct 26, 2022 11:53 pm

    avatar
    New2Tubez


    Posts : 147
    Join date : 2018-03-20
    Location : NY

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    Post by New2Tubez Wed Oct 26, 2022 11:57 pm

    Just saw your location-

    I got serious road rash on the alpine slide summer of '94.
    Also visit N Adams every once in a while.
    avatar
    mijohn


    Posts : 111
    Join date : 2013-06-19

    VTA-120 Possible Pentode/Triode Switch Problems Empty Re: VTA-120 Possible Pentode/Triode Switch Problems

    Post by mijohn Thu Oct 27, 2022 12:24 am

    As to your previous problem with the switch. Flipping the switch on the fly may have caused arcing and it's probably good practice to power off before flicking the switch.
    jimmeq
    jimmeq


    Posts : 60
    Join date : 2017-02-24
    Location : Six Miles West of Jiminy Peak Ski Resort

    VTA-120 Possible Pentode/Triode Switch Problems Empty Re: VTA-120 Possible Pentode/Triode Switch Problems

    Post by jimmeq Sat Oct 29, 2022 12:36 pm

    Thanks for the link. I'll try it before I start any part replacement. I'll report back what I find. Again, thanks for the replies.

    I'm pretty sure the switch took the hit from my shorting debacle. Here's the link to the story. Some pics are no longer accessible. https://dynacotubeaudio.forumotion.com/t4151-beautiful-sound-of-my-vta-st120drt1-part-2

    These pictures should be visible- https://photos.app.goo.gl/QNwFYshyzzmwaY2W9

    So, I don't usually switch between modes while the amp is on. Just when it was silent on the right channel. I learned that lesson the hard way.



    Last edited by jimmeq on Sat Oct 29, 2022 12:42 pm; edited 1 time in total (Reason for editing : Added some more info and link.)
    jimmeq
    jimmeq


    Posts : 60
    Join date : 2017-02-24
    Location : Six Miles West of Jiminy Peak Ski Resort

    VTA-120 Possible Pentode/Triode Switch Problems Empty Re: VTA-120 Possible Pentode/Triode Switch Problems

    Post by jimmeq Mon Oct 31, 2022 6:03 pm

    I swapped the inputs and got sound from both channels. Thank you all for the information. I'm glad the amp is OK. Whew.

    New2Tubez likes this post


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