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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


    Speaker load on ST-120

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    monkuboy

    Posts : 44
    Join date : 2016-03-23

    Speaker load on ST-120 Empty Speaker load on ST-120

    Post by monkuboy Thu Jun 03, 2021 8:46 pm

    I know you are not supposed to run a tube amp without having speakers connected to the terminals, but I was wondering if it is harmful to the amp if the amp is on with no speakers connected, but there is no signal being input to the amp?
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    yel17

    Posts : 5
    Join date : 2015-04-23
    Age : 72
    Location : Chicagoland

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    Post by yel17 Thu Jun 03, 2021 10:55 pm

    No speakers, no input signal, no problem,
    peterh
    peterh

    Posts : 1565
    Join date : 2012-12-25
    Location : gothenburg, sweden

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    Post by peterh Fri Jun 04, 2021 1:16 am

    monkuboy wrote:I know you are not supposed to run a tube amp without having speakers connected to the terminals, but I was wondering if it is harmful to the amp if the amp is on with no speakers connected, but there is no signal being input to the amp?
    It's still dangerous. A thump on the power line or an airborne discharge will create a signal that is amplified and potentially damaging the output transformer.

    If you need to have amp powered on without load, shorting the output will protect the amp.
    cci1492
    cci1492

    Posts : 328
    Join date : 2016-05-09
    Age : 60
    Location : NJ

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    Post by cci1492 Fri Jun 04, 2021 8:22 am

    I know you meant input.

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    peterh
    peterh

    Posts : 1565
    Join date : 2012-12-25
    Location : gothenburg, sweden

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    Post by peterh Fri Jun 04, 2021 10:25 am

    cci1492 wrote:I know you meant input.
    No i ment shorting the output !
    This is to prevent high voltages building up in the output transformer.

    Shorting a tube amp has no immidiate danger, it will increase temp on the plates if
    shorted and signal applied.

    cci1492
    cci1492

    Posts : 328
    Join date : 2016-05-09
    Age : 60
    Location : NJ

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    Post by cci1492 Fri Jun 04, 2021 10:30 am

    Interesting, I thought that winding should always see a load. Very good then, learned something new. So "A thump on the power line or an airborne discharge will create a signal that is amplified and potentially damaging the output transformer" is not a problem with the output shorted. Good to know, thanks.
    aguaazul
    aguaazul

    Posts : 132
    Join date : 2012-07-08
    Age : 61
    Location : Livermore, CA

    Speaker load on ST-120 Empty Re: Speaker load on ST-120

    Post by aguaazul Sat Jun 12, 2021 6:24 pm

    I connect up a 8 Ohm 100W Dummy Load to the speaker posts on all amps when working on them with power or testing them. It's safer.  I screwed them down to a 10" piece of 2 x 4, when I go to work on an amp on the bench, it comes out.  I used 2 - 4 ohm - 100W power resistors connected to aluminum angle as a heatsink gives 8 ohm @ 100 watts. Mounted these to the aforementioned 2 x 4.   Easy to bang one of these out, you'll be glad you did.

    Cheers,

    Aguaazul

    8 Ohm Dummy Load


    Last edited by aguaazul on Sat Jun 12, 2021 6:28 pm; edited 1 time in total (Reason for editing : Fixed Photo's)

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    edman44

    Posts : 14
    Join date : 2021-06-14
    Age : 59
    Location : PENNSYLVANIA

    Speaker load on ST-120 Empty Re: Speaker load on ST-120

    Post by edman44 Wed Jun 16, 2021 7:38 pm

    Hello Aguaazul,
    I just bought a VTA ST-120 KIT. I was reading your post and wanted to build your dummy load. And was wondering where you bought your resistors from? Sure sounds like something I am going to need. Thanks,
    aguaazul
    aguaazul

    Posts : 132
    Join date : 2012-07-08
    Age : 61
    Location : Livermore, CA

    Speaker load on ST-120 Empty Re: Speaker load on ST-120

    Post by aguaazul Wed Jun 16, 2021 7:59 pm

    edman44 wrote:Hello Aguaazul,
                           I  just bought a  VTA ST-120 KIT. I was reading your post and wanted to build your dummy load. And was wondering where you bought your resistors from? Sure sounds like something I am going to need. Thanks,

    I got them from Amazon!

    uxcell 100W 4 Ohm Screw Tap Mounted Aluminum Housed Wirewound Resistors 2 Pcs

    Get 4 of them to get your 8 ohms.

    Cheers,

    Aguaazul


    Last edited by aguaazul on Wed Jun 16, 2021 10:36 pm; edited 1 time in total (Reason for editing : Fix Link)

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