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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


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    SP14 losing right channel when warm

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    Dusterdave


    Posts : 8
    Join date : 2017-04-09

    SP14 losing right channel when warm Empty SP14 losing right channel when warm

    Post by Dusterdave Fri Nov 24, 2023 12:32 pm

    Hey everyone,
    I’m experiencing a problem with my SP14. Everything is great until 1 to 2 hours of listening then the right channel cuts out. I run 12SN7 tubes and leaning to those tubes as the culprit. Any suggestions?
    Thanks Dave
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    Rec


    Posts : 76
    Join date : 2020-03-11

    SP14 losing right channel when warm Empty Re: SP14 losing right channel when warm

    Post by Rec Sat Nov 25, 2023 9:20 am

    I’d go through the solder joints on the board. Maybe a tube socket? Wonky solder Joints can open up when heated.
    Dave_in_Va
    Dave_in_Va


    Posts : 445
    Join date : 2013-04-02
    Location : Mid. VA

    SP14 losing right channel when warm Empty Re: SP14 losing right channel when warm

    Post by Dave_in_Va Sun Nov 26, 2023 10:37 am

    You mean 6SN7s, right?

    I had the same problem with my SP 14. Is your SP 14 an older unit?

    I ended up sending mine back to Roy twice. Mine was a very early SP 14 and the old ones had an un undersized heat sink and an an out of spec filament transformer.
    That may or may not be your problem.
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    Dusterdave


    Posts : 8
    Join date : 2017-04-09

    SP14 losing right channel when warm Empty Re: SP14 losing right channel when warm

    Post by Dusterdave Mon Nov 27, 2023 12:34 am

    Thanks all.
    I checked all solder joints tonight. Nothing looked bad but just to be safe I resoldered all the tube sockets, the power transistors, and everything that could be suspect. I only had time to play 1 lp, it worked fine but tomorrow I’ll let it play for a few hours and keep my fingers crossed!
    Dave, I run 12SN7s, they are essentially the same but operate at 12v instead of 6v and can be bought for less.
    Oh, I also checked all voltages on the build sheet. Everything looked good both when first turned on and after being powered for 2 hours.
    Again I will test tomorrow.
    Thanks for the feedback!

    10-E-C likes this post

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    Dusterdave


    Posts : 8
    Join date : 2017-04-09

    SP14 losing right channel when warm Empty Re: SP14 losing right channel when warm

    Post by Dusterdave Mon Nov 27, 2023 9:52 pm

    Hey all,
    I still have the problem. Yesterday I checked and resoldered, today it again lost the right channel after it warmed up. I have installed new tubes (including the rectifier). Any suggestions?
    Dave, I checked all voltages when warm yesterday and everything seemed okay so probably not the transformer?
    Dave_in_Va
    Dave_in_Va


    Posts : 445
    Join date : 2013-04-02
    Location : Mid. VA

    SP14 losing right channel when warm Empty Re: SP14 losing right channel when warm

    Post by Dave_in_Va Mon Nov 27, 2023 10:16 pm

    I'm not a tech but my SP 14 was doing exactly what yours is doing as I said.
    How old is your SP 14? Is changing over to 12SN7s a common mod?

    Like I said. Roy had to work on mine twice.
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    Dusterdave


    Posts : 8
    Join date : 2017-04-09

    SP14 losing right channel when warm Empty Re: SP14 losing right channel when warm

    Post by Dusterdave Mon Nov 27, 2023 11:42 pm

    Hey Dave,
    My unit is about 7 years old so it could be the transformer. My thinking is if the voltages were correct after warming up yesterday the transformer should be okay but I think I will perform another voltage test tomorrow after it has been powered up for at least 2 hours.
    I would say the 12SN7 is a fairly common modification and was suggested by Roy at the time of purchase. I just purchased 4 NOS 12SN7s for under $30.

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