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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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    ST70 Attenuator Noise

    Bugs
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    Bugs


    Posts : 90
    Join date : 2009-04-17
    • Post n°1

    ST70 Attenuator Noise Empty ST70 Attenuator Noise

    Post by Bugs Tue Jun 14, 2011 4:00 pm

    I installed a stepped volume attenuator in my ST70. A very similar setup to the attenuator offered by Bob. In fact I was using one of Bob's attenuators until I accidentally wacked the center shaft and knocked it out of operation. I used Bob's setup instructions to install the second attenuator. When I turn the amp on I get a loud 60 cycle hum through the speakers that is unaffected by the volume control. I'm guessing that I have the ground wrong? I'm running the ground wire from the ground post on the input jack to the center post on the attenuator. Any ideas?

    Thanks
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    Bob Latino
    Bob Latino
    Bob Latino
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    Location : Massachusetts
    • Post n°2

    ST70 Attenuator Noise Empty Re: ST70 Attenuator Noise

    Post by Bob Latino Tue Jun 14, 2011 5:49 pm

    Bugs wrote:I installed a stepped volume attenuator in my ST70. A very similar setup to the attenuator offered by Bob. In fact I was using one of Bob's attenuators until I accidentally wacked the center shaft and knocked it out of operation. I used Bob's setup instructions to install the second attenuator. When I turn the amp on I get a loud 60 cycle hum through the speakers that is unaffected by the volume control. I'm guessing that I have the ground wrong? I'm running the ground wire from the ground post on the input jack to the center post on the attenuator. Any ideas?

    Thanks

    Hi Bugs,

    Check the photo below. With the rotation shaft facing away from you and the solder terminals pointed UP ..

    1. The far LEFT attenuator terminal should be the GROUND terminal and it should go to the outer ground tab on the input jack. There should also be a wire there that goes to the ground eyelet on he driver board.
    2. The CENTER attenuator terminal goes to the driver board "IN".
    3. The far RIGHT attenuator terminal goes to the CENTER PIN on the INPUT jack.

    Bob

    ST70 Attenuator Noise Attenuatorinstructions
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    Bugs
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    • Post n°3

    ST70 Attenuator Noise Empty Re: ST70 Attenuator Noise

    Post by Bugs Wed Jun 15, 2011 9:30 am

    Thanks Bob,

    I did have the attenuator wired correctly, however I had removed to ground wire to the board. I'll correct that tonight and see what happens.

    Cheers
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    Bugs
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    • Post n°4

    ST70 Attenuator Noise Empty Re: ST70 Attenuator Noise

    Post by Bugs Thu Jun 16, 2011 9:14 am

    Did the trick, thanks again.
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    • Post n°5

    ST70 Attenuator Noise Empty Re: ST70 Attenuator Noise

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