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    MK III woes...

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    grizzinca

    Posts : 40
    Join date : 2012-01-01

    Re: MK III woes...

    Post by grizzinca on Sat Aug 10, 2013 10:17 pm

    Thanks Bob. I built an st70 last winter, used a 2 prong plug and never hab this issue. A good nights rest and I'll give a try in the morning. Thanks again. By the way, my preamp is a 6 months old Rugue Metis that I use with the st70 and performs perfect. And yes the interconnects are in place as well as speaker load.

    Bob Latino
    Admin

    Posts : 2411
    Join date : 2008-11-26
    Location : Massachusetts

    Re: MK III woes...

    Post by Bob Latino on Sat Aug 10, 2013 10:32 pm

    grizzinca wrote:Thanks Bob. I built an st70 last winter, used a 2 prong plug and never hab this issue. A good nights rest and I'll give a try in the morning. Thanks again. By the way, my preamp is a 6 months old Rugue Metis that I use with the st70 and performs perfect. And yes the interconnects are in place as well as speaker load.
    If your Rogue preamp also has a 3 wire cord then it could be a ground loop .. Try the cheater plug ..

    Bob

    grizzinca

    Posts : 40
    Join date : 2012-01-01

    Re: MK III woes...

    Post by grizzinca on Sun Aug 11, 2013 7:08 pm

    http://s1303.photobucket.com/user/grizzinca/media/image_zps1eeb8b8d.jpg.html?sort=3&o=1http://s1303.photobucket.com/user/grizzinca/media/image_zps2161cb99.jpg.html?sort=3&o=0http://s1303.photobucket.com/user/grizzinca/media/image_zps89f6c131.jpg.html?sort=3&o=2.
    So I used the cheater plugs as explained and there was a slight change for the better, but still a noticeable hum. Switched power cord to its own outlet one one amp, that helped even more. Ran the amps for about 10 minutes and on both amps v2 became glowing red, so I shut both amps down. Doesn't appear I did any damage. Amps sounded ok. Also I disconnected the rca's from the preamp and shorted out the end and the hum stayed. Outputs biased ok. Steady. Trying to give as much info, along with more recent pics. The hum was present using different preamps. Didn't change.hope the pics are of help, could really use some expert eyes on this. Thanks, Mike

    DynakitParts
    Admin

    Posts : 183
    Join date : 2008-11-30

    MK III

    Post by DynakitParts on Sun Aug 11, 2013 9:15 pm

    Hi,
    Looking at the photos...I do not see the 680 ohm 1 watt resistor connected to the speaker output terminals between the Black & Yellow output transformer leads. Is this connected somewhere else or is this resistor located on the circuit board?

    Kevin

    quad44

    Posts : 18
    Join date : 2009-06-08

    Re: MK III woes...

    Post by quad44 on Mon Aug 12, 2013 12:28 pm

    In an earlier post Roy had asked about grounding. This post is in continuation of that thought.
    The only ground reference to the power supply quad capacitor in your picture is through the twist mounting tab, the black wire and the socket of V1. The Red/Yel wire(CT of the X'frmr) connects to the chassis via the 3 lug terminal strip.
    You are depending on a mechanical connection to complete the B+ circuit.
    Have a look at the mechanical connections between the chassis and V1 mounting fasteners and the fasteners between the 3 lug terminal and the chassis. Tighten up all the fasteners. Oxidation between metal surfaces can be problematic when talking about current flow.
    As a possible solution you can run a ground wire from the Red/Yel wire to the ground tab of the quad cap and another ground wire from the VTA board directly to the same ground tab of the quad cap. What you are doing is effectively bypassing any resistance in the grounding circuit(s).
    Good luck and please bleed the quad cap before you get near them.

    grizzinca

    Posts : 40
    Join date : 2012-01-01

    Re: MK III woes...

    Post by grizzinca on Mon Aug 12, 2013 9:22 pm

    Thanks for your help. I'll 're-ground' as per your reply. Hopefully this will cure the hum. Would a bad ground cause output tubes (v2)in both amps to overheat? Again, thanks for the help.
    Mike

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