Annoying Buzzing, need help

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Annoying Buzzing, need help

Postby zippy1540 » Fri Mar 10, 2017 11:28 am

Built a junk box guitar amp. http://monster.partyhat.co/article/micr ... mp-R2B.pdf
12ax7 feeding a 6aq5. See attached schematic. The only changes i made were the 5.6K to the 6aq5 is a 5.1k and the power supply is a full wave since the transformer i had was not center tapped. the buzz goes away when i short the input. What am i missing?
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Re: Annoying Buzzing, need help

Postby zippy1540 » Fri Mar 10, 2017 11:30 am

It is wired point to point so i'm thinking about ripping it apart and making up a tagboard for it. I've ohmed out every resistor and verified it's wired according to the schematic.
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Re: Annoying Buzzing, need help

Postby Geek » Fri Mar 10, 2017 1:19 pm

Hi,

Sounds like it may be oscillating.

Check your lead dressing (wire routing is VERY important on guitar amps)

A pic of the underside of the chassis might help us further.

Cheers!
-= Gregg =-
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Re: Annoying Buzzing, need help

Postby zippy1540 » Sat Mar 18, 2017 12:08 pm

Got it figured out. The Can cap i was re utilizing was bad plus the guitar i was using had a bad ground from the pickups to the jack. Swapped Caps with another one i had laying around and it was quiet as hell.
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Re: Annoying Buzzing, need help

Postby Geek » Sat Mar 18, 2017 12:25 pm

Solution found. Awesome! (y)
-= Gregg =-
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Re: Annoying Buzzing, need help

Postby zippy1540 » Sat Mar 18, 2017 1:17 pm

Guess that's the danger of using used can caps although building a guitar amp from scrap parts that guitar players love is cool. I can't play a chord to save my life but i can build the amps for those who can. Biased a russian Mig 60 last night. The genius got under it ad cranked the bias until the tubes had a catastrophic meltdown. Told the guy he was lucky he didn't burn out the output transformer.
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Re: Annoying Buzzing, need help

Postby Geek » Sun Mar 19, 2017 1:25 pm

Heh, I had a guitar amp customer like that. When he brought it in for it's 5th set of EL34's in 6 months, I put the bias inaccessible from the outside. He was mad as heck, but didn't have to re-tube for two years! (lol)
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