5f1 champ static sounds

Discussion in 'Shock Brother's DIY Amps' started by Linkjr, May 21, 2019.

  1. Linkjr

    Linkjr Tele-Meister

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    Hi Guys just when my 5f1 was all cool I started getting static on notes.

    After considerable testing it only happens after pushing the amp and is affected by volume.
    it's not a scratchy volume pot as doesn't happen whilst I adjust it.

    Have reflowed all joints and have fitted new tubes, have fitted new tube sockets and still remains so .. since I'm all out of ideas.. thought I would try the experts over in this neck of the woods!
     
  2. JuneauMike

    JuneauMike Friend of Leo's

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    Including a rectifier tube? Did you also clean and confirm tension on the tube sockets? How bout guitar cables? Have you tried a different cable?
     
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  3. Linkjr

    Linkjr Tele-Meister

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    Thanks for looking JuneauMike, yes and yes
     
  4. JuneauMike

    JuneauMike Friend of Leo's

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    How are your plate and cathode resistors? Do you know what wattage they are? Any obvious signs of heat or other problems? Go ahead and try chopsticking them to see if you can get any reaction from the static.

    Oh, check your speaker cables as well.
     
  5. Linkjr

    Linkjr Tele-Meister

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    the cathode resistor powertube is a 470 5w, replaced one of the 100k plate resistors thinking looked suspect but measured ok , no obvious signs of excessive heat, 6v6 giving off a lot of heat but my b+ Measured recently is within spec

    Speaker cable also checked.
     
  6. JuneauMike

    JuneauMike Friend of Leo's

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    What type/wattage of plate resistor does it have? Is it 1/4 watt carbon comp?
     
  7. Linkjr

    Linkjr Tele-Meister

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    100k Carbon comp 1/2 watt
     
  8. JuneauMike

    JuneauMike Friend of Leo's

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    Hmm. Total shot in the dark, but do you have a 1 watt? Or a carbon film of the same value?

    Also, when you wiggle to tubes do you get any change in the static? I think you said earlier that you don't.
     
  9. JuneauMike

    JuneauMike Friend of Leo's

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    I think at some point it may be good for you to post some pics of the inside of the amp. Get good clear photos of the board, the control plate, the tube sockets.
     
  10. dan40

    dan40 Tele-Afflicted Silver Supporter

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    I had a loose speaker connection cause that same problem in a build a few years back. I was using the push on speaker connectors for quick speaker rolling and one of them was a bit loose. It caused a bit of static in the sound whenever I played loud enough to cause the cab to vibrate. Soldering the speaker wires onto the speaker tabs solved the problem for me.
     
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  11. peteb

    peteb Friend of Leo's

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    Good idea to check the speaker connection.



    Should be some kind of bad / intermittent connection in the signal path.


    The plate resistor is not in the signal path and the hissing or bacon frying sound they make is all the time including idle.




    Is there any way to isolate the problem? Pulling tubes I don’t think will help but what about an oscilloscope or people make testing tools that can listen to the circuit at different places, all it takes is another amp.
     
  12. Nickfl

    Nickfl Tele-Afflicted

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    Is it loud static, or just a background fuzz behind the notes? Does it sound kind of like plugging a guitar into an amp that's already on?
     
  13. JuneauMike

    JuneauMike Friend of Leo's

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    It carries high voltage DC and a cold solder there would cause intermittent noise when the amp heats up. You are describing shot noise, which is not dependent on temperature.
     
  14. peteb

    peteb Friend of Leo's

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    The key is that the static is on the note. The signal causes it, it should be in the signal path.



    I take it back, the plate resistor is in the signal path, on its path to ground. A disconnection here would be a discontinuation of the signal. I was noting that typical plate resistor noise (from carbon comp resistors?) is a background noise, not on the note.
     
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  15. JuneauMike

    JuneauMike Friend of Leo's

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    I agree, shot noise is background and constant. But with a faulty solder there the noise theoretically could be caused not by the note, but the vibration. Chopsticks should eliminate the possibility.
     
  16. bigguy12321

    bigguy12321 Tele-Meister

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    Just a thought. I just has a speaker mounting screw loosen up and give a weird buzz when pushed hard. Turned out speaker was a bit under torqued on one corner... You know, the round corner...

    a
     
  17. D'tar

    D'tar Friend of Leo's

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  18. Linkjr

    Linkjr Tele-Meister

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    Thanks all for all the suggestions now to get to work

    I was fooled by loose screws once not this time, nothing loose on speaker.

    Will reflow solder the joint back of board between the 2 plate resistors and the filter cap.

    Can the problem be localised to the plate resistors at this point? Will post some pics once I check above
     
  19. JuneauMike

    JuneauMike Friend of Leo's

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    Unfortunately, no. I wouldn't presume it's the plate load resistors. I think good resolution pics will help people more at this point, otherwise we're just guessing about some of the usual suspects.

    Are you reflowing solder joints that look bad, or are you just reflowing everything? You said something about replacing the tube sockets earler, is that correct? What made you decide to replace them.

    Also, this guy is asking important questions. Responding to them will be helpful. You are describing a noise, which can be notoriously subjective. I still have a hard time distinguishing between 60hz and 120hz hum, as an example. One man's hum is another man's buzz. So, you know ....
     
    Last edited: May 22, 2019
  20. Linkjr

    Linkjr Tele-Meister

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    Unfortunately reflowed the joints but after playing for hard for 2 mins the faint crackle sounding like Velcro unfastening under the notes started again.
    See gut shots below
    IMG_1287.JPG IMG_1288.JPG IMG_1290.JPG
     
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