The Dynaco Tube Audio Forum

Would you like to react to this message? Create an account in a few clicks or log in to continue.
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


    Hum in PH14

    Pillo69
    Pillo69

    Posts : 176
    Join date : 2012-04-11
    Location : Granada (España)

    Hum in PH14 - Page 2 Empty Re: Hum in PH14

    Post by Pillo69 on Thu Jun 25, 2020 5:28 pm

    From the PCB and components that you provide in the image, I see it very-very similar to the EAR834.
    If you look for the EAR scheme you may find the solution.
    Since I understand that you do not have more data from that PCB.
    DavidR
    DavidR

    Posts : 83
    Join date : 2017-08-10
    Location : MetroWest, MA

    Hum in PH14 - Page 2 Empty Re: Hum in PH14

    Post by DavidR on Thu Jun 25, 2020 6:12 pm

    Thanks for your input.
    My understanding is that my board is a clone of theEAR834 but has had modifications. The schematic for the audio signal that was provided is for the EAR834 and it is not the same.

    Hum in PH14 - Page 2 Ph14_a12
    Pillo69
    Pillo69

    Posts : 176
    Join date : 2012-04-11
    Location : Granada (España)

    Hum in PH14 - Page 2 Empty Re: Hum in PH14

    Post by Pillo69 on Fri Jun 26, 2020 6:12 am

    I only see a difference to the scheme with the EAR the decrease in the value of C19, C20 and C21. From 22u to 10u.
    Usually it usually increases, I have seen there up to 100u !.
    R49 is fine for new production valves, for NOS valves a value of 680k better adjusts the bass response below 100Hz.

    You can test by placing a 0.1U / 63v capacitor between the filament supply pins of the three valves. From the bottom of the PCB. Although I should check with Roy first.
    DavidR
    DavidR

    Posts : 83
    Join date : 2017-08-10
    Location : MetroWest, MA

    Hum in PH14 - Page 2 Empty Re: Hum in PH14

    Post by DavidR on Fri Jun 26, 2020 9:03 am

    Those caps on my board are 33uF.

    Here's a few more pics of my question > My style board and an earlier one showing a cap where I have a jumper wire.

    Hum in PH14 - Page 2 Ph14_a13

    Hum in PH14 - Page 2 Ph14eb12
    avatar
    rjpjnk

    Posts : 264
    Join date : 2018-07-18

    Hum in PH14 - Page 2 Empty Re: Hum in PH14

    Post by rjpjnk on Fri Jun 26, 2020 1:28 pm

    I don't understand. I assume the blue board is yours and the green is the older board? Both boards appear to have a small red thing attached at the corner where you circled the component. Are these not both capacitors?
    DavidR
    DavidR

    Posts : 83
    Join date : 2017-08-10
    Location : MetroWest, MA

    Hum in PH14 - Page 2 Empty Re: Hum in PH14

    Post by DavidR on Fri Jun 26, 2020 1:55 pm

    The blue board is the same style/model as mine. My board does not have that little cap. It has a jumper wire.
    avatar
    rjpjnk

    Posts : 264
    Join date : 2018-07-18

    Hum in PH14 - Page 2 Empty Re: Hum in PH14

    Post by rjpjnk on Fri Jun 26, 2020 2:13 pm

    So neither of the boards in the pics are yours?

    I searched everywhere online and cannot find a clear picture of both sides of these boards. I found only the bottom, and there are no connections to that c21/c25/jumper mystery component.Can you send a pic of the top looking down at this point on your board so I can see where that traces go?

    One pic I did find it looked like the little cap was between board ground and chassis, but it wasn't clear enough to be certain. Send a pic of your PH14 please showing this component location.

    EDIT: While you're at it, send pics showing all the wires connected to all the boards. I can't see them in the first pic because they are obscured by the front panel.
    DavidR
    DavidR

    Posts : 83
    Join date : 2017-08-10
    Location : MetroWest, MA

    Hum in PH14 - Page 2 Empty Re: Hum in PH14

    Post by DavidR on Fri Jun 26, 2020 2:50 pm

    OK but it will be a day or so as I'll have to pull it from the rack again.

    In the meantime Roy contacted me and said that he found installing this cap usually made the hum worse.

    Sponsored content

    Hum in PH14 - Page 2 Empty Re: Hum in PH14

    Post by Sponsored content


      Current date/time is Wed Oct 21, 2020 11:25 pm