The Dynaco Tube Audio Forum

Dedicated to the restoration and preservation of all original Dynaco tube audio equipment - Customer support for Dynaco VTA tube amp kits, all Tubes4hifi.com products and all Dynakitparts.com products


    VAC Dynaco PAS

    Share

    Pillo69

    Posts : 105
    Join date : 2012-04-11
    Location : Granada (España)

    VAC Dynaco PAS

    Post by Pillo69 on Sat Jun 14, 2014 11:34 am

    Available in the RCA output PAS 0.3 VAC, brings Hum and electric differential jumping house.

    The voltage scheme below.

    Anyone know the problem?.


    peterh

    Posts : 679
    Join date : 2012-12-25
    Location : gothenburg, sweden

    Re: VAC Dynaco PAS

    Post by peterh on Sat Jun 14, 2014 12:21 pm

    Voltages seems ok.
    But i do not understand your question. What is the problem ?
    And is this an unmodified PAS-3 ?

    Pillo69

    Posts : 105
    Join date : 2012-04-11
    Location : Granada (España)

    Re: VAC Dynaco PAS

    Post by Pillo69 on Sat Jun 14, 2014 4:42 pm

    Yes, it is an original PAS. 240v transformer rewind.

    There is a leak that generates VAC HUM me, and when I connect to a device with RCA grounding differential rises from the house.

    sorry for my english.

    tubes4hifi
    Admin

    Posts : 1292
    Join date : 2008-11-30

    Re: VAC Dynaco PAS

    Post by tubes4hifi on Sat Jun 14, 2014 4:59 pm

    pin 7 is a grid, you can't expect to be able to measure grid voltages with most meters, as they will load the circuit down
    that's the huge advantage of an old fashioned vacuum tube voltmeter, which has 11 megohm impedance or great.
    Most modern DVMs only have around 1Mohm impedance.

    If you are getting hum, most likely your source isn't grounded the same as the PAS preamp, or there is a poor ground connection somewhere, or more likely a ground loop.

    Pillo69

    Posts : 105
    Join date : 2012-04-11
    Location : Granada (España)

    Re: VAC Dynaco PAS

    Post by Pillo69 on Sat Jun 14, 2014 6:18 pm

    tubes4hifi wrote:pin 7 is a grid, you can't expect to be able to measure grid voltages with most meters, as they will load the circuit down
    that's the huge advantage of an old fashioned vacuum tube voltmeter, which has 11 megohm impedance or great.
    Most modern DVMs only have around 1Mohm impedance.  

    If you are getting hum, most likely your source isn't grounded the same as the PAS preamp, or there is a poor ground connection somewhere, or more likely a ground loop.


    The 0.3 VAC in the line-out are also due to that ground loop?.
    Thank you.

    tubes4hifi
    Admin

    Posts : 1292
    Join date : 2008-11-30

    Re: VAC Dynaco PAS

    Post by tubes4hifi on Sat Jun 14, 2014 6:57 pm

    that's probably the hum you are hearing!

    Pillo69

    Posts : 105
    Join date : 2012-04-11
    Location : Granada (España)

    Re: VAC Dynaco PAS

    Post by Pillo69 on Mon Jun 16, 2014 6:07 pm

    I have replaced three Phono inputs wiring, I put OFC screened cable, the HUM is gone, but current over the mass still exists.



    Pillo69

    Posts : 105
    Join date : 2012-04-11
    Location : Granada (España)

    Re: VAC Dynaco PAS

    Post by Pillo69 on Wed Jun 18, 2014 6:27 am

    I have replaced the PAS volume potentiometer with an ALPS (100 k) without loudness.

    I have read in several places that the resistance of 4 k 7 is due to start. Where I put it?.

    Pillo69

    Posts : 105
    Join date : 2012-04-11
    Location : Granada (España)

    Re: VAC Dynaco PAS

    Post by Pillo69 on Sun Dec 21, 2014 9:10 pm

    Update the thread to show the solution shunt to ground voltage.

    The problem was .02 capacitor next to the power switch. I used the tester and showed me the correct value, however as a last resort I've replaced and the problem is resolved.

    Sponsored content

    Re: VAC Dynaco PAS

    Post by Sponsored content Today at 12:01 pm


      Current date/time is Thu Dec 08, 2016 12:01 pm