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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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    2 quick newbie questions

    Normster
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    Normster


    Posts : 3
    Join date : 2009-08-19
    • Post n°1

    2 quick newbie questions Empty 2 quick newbie questions

    Post by Normster Wed Aug 26, 2009 11:05 am

    First, I received my chassis kit and driver board in record time! Thanks Bob and Roy. After looking things over, I have a couple of questions:

    1. Is it OK to use a grounded cord or will this cause ground loop problems?

    2. The schematic shows 2 cathode bypass caps (47uF) but they were not in my board kit. Have these been eliminated to reduce gain or should I install them? (Don't worry about sending replacement parts. I have them in stock.)

    Thanks again for the fast shipping!
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    Bob Latino
    Bob Latino
    Bob Latino
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    Join date : 2008-11-26
    Location : Massachusetts
    • Post n°2

    2 quick newbie questions Empty Re: 2 quick newbie questions

    Post by Bob Latino Wed Aug 26, 2009 4:44 pm

    Normster wrote:First, I received my chassis kit and driver board in record time! Thanks Bob and Roy. After looking things over, I have a couple of questions:

    1. Is it OK to use a grounded cord or will this cause ground loop problems?

    2. The schematic shows 2 cathode bypass caps (47uF) but they were not in my board kit. Have these been eliminated to reduce gain or should I install them? (Don't worry about sending replacement parts. I have them in stock.)

    Thanks again for the fast shipping!

    Hi Norm,

    1. Using a grounded cord on the VTA ST-70 may or may not cause an issue with hum. If your preamp has a 3 wire cord and the amp has a two wire then using the amp with that preamp could cause a ground loop. If you want to TRY a 3 wire cord with the amp and ground the third wire to the chassis - do it and run the amp alone and note the hum. Then run the amp and lift the ground and see which way has less hum. By the way, anytime you test the amp for hum plug in two interconnects and short between the center pin and the outer shield on the OTHER END of both interconnects. If an ST-70's input jacks are left open they will pick up some hum and noise.

    2. Those two 47 uF 50 volt caps are not used anymore with the VTA driver board. It was found that the elimination of these two small capacitors lowered gain a small amount and also lowered distortion by a small amount. Personally I can't hear any difference with those two caps in the circuit or out of the circuit.

    Bob


    Last edited by Bob Latino on Wed Aug 26, 2009 7:38 pm; edited 1 time in total
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    Normster
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    Normster


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    Join date : 2009-08-19
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    Post by Normster Wed Aug 26, 2009 7:22 pm

    Thanks, Bob!
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