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


    GZ-34 Hum?

    Share

    harpy

    Posts : 94
    Join date : 2012-02-04

    GZ-34 Hum?

    Post by harpy on Mon May 06, 2013 10:11 pm

    I rebuilt my Mk III's and noticed a little hum on both. I just assumed it was the transformers, but the more I listen it seems to be coming from my GZ-34's. The amps were pretty much rebuilt stock except for an SDS Labs board in place of the quad cap. I hear no hum from the speakers. I was wondering if it was normal or if they might be getting too much juice from the 50uF section of the SDS board. Do tubes hum even the hum? It is fairly and hard to pin point. Really don't care about the hum just don't want to destroy the NOS tubes.

    j beede

    Posts : 328
    Join date : 2011-02-07
    Location : California

    Re: GZ-34 Hum?

    Post by j beede on Mon May 06, 2013 11:09 pm

    Have you tried powering up your amps with the rectifiers out to see if the hum goes away? Do you have silicon diodes ahead of the GZ-34 to "pre-rectify" the ac?

    j beede

    Posts : 328
    Join date : 2011-02-07
    Location : California

    Re: GZ-34 Hum?

    Post by j beede on Mon May 06, 2013 11:20 pm

    FYI: JJ, Telefunken, Philips, and GE all specify Cmax=60µF for GZ-34/5AR4. It is not unusual for experienced tube amp fans to limit capacitance on the rectifier side of the choke to much less than 60µF.

    harpy

    Posts : 94
    Join date : 2012-02-04

    Re: GZ-34 Hum?

    Post by harpy on Tue May 07, 2013 3:49 pm

    Yes it's the tubes. Would the rectifier tube diode mode sticky apply for the pre-rectify?

    harpy

    Posts : 94
    Join date : 2012-02-04

    Re: GZ-34 Hum?

    Post by harpy on Tue May 07, 2013 6:31 pm

    Also, J Beede are you running DQ-10's?

    j beede

    Posts : 328
    Join date : 2011-02-07
    Location : California

    Re: GZ-34 Hum?

    Post by j beede on Wed May 08, 2013 12:35 am

    harpy wrote: Yes it's the tubes. Would the rectifier tube diode mode sticky apply for the pre-rectify?

    Yes, I like to use diodes as 1/2 wave rectifiers ahead of the 5AR4. The "yellow sheet" mod in the sticky is worth doing. How much capacitance do you have on the side of the choke away from the GZ-34?

    j beede

    Posts : 328
    Join date : 2011-02-07
    Location : California

    Re: GZ-34 Hum?

    Post by j beede on Wed May 08, 2013 1:20 am

    harpy wrote:Also, J Beede are you running DQ-10's?

    No Dahlquists. Quad 2-ways and assorted Magneplanars. My avatar is one of my Quad ESLs from the "old" days.
    ...j

    harpy

    Posts : 94
    Join date : 2012-02-04

    Re: GZ-34 Hum?

    Post by harpy on Wed May 08, 2013 10:33 pm

    I run 118.5 AC soft start into both. The voltages are good through out the amp. If I am on the right page the value would be 50uF (measures 53uf). Here's a shot the small yellow Teflon wire goes from the GZ-34 to the SDS Board.


    harpy

    Posts : 94
    Join date : 2012-02-04

    Re: GZ-34 Hum?

    Post by harpy on Fri May 17, 2013 4:15 pm

    I tried switching out rectifier tubes and hum remains. I haven't done the yellow sticky mod yet because I would like to see if I can find the issue. The only thing I can think of is a bad ground on the SDS boards. The green wire is the grounding point and it grounds out where the 3 terminal board where the blue bias cap is. Any other thoughts?

    harpy

    Posts : 94
    Join date : 2012-02-04

    Re: GZ-34 Hum?

    Post by harpy on Fri May 17, 2013 6:54 pm

    If you look at the picture you see the red transformer lines going to pins 4 and 6. If you look at my amp in it's present state you would see the red lines going to pins 4 and 5. Gremlins? Embarassed No more hum.

    Sponsored content

    Re: GZ-34 Hum?

    Post by Sponsored content Today at 8:05 am


      Current date/time is Tue Dec 06, 2016 8:05 am