Custom 20 hiss

Discussion in 'Amplifiers' started by godwentpunk, May 18, 2018.

  1. godwentpunk

    godwentpunk New Member

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    Is this normal for this amp? Seems loud to me. My volume pot definitely sounds bad, I sprayed some cleaner but that did not help.



    Joe...
     
  2. AP515

    AP515 Mostly Normal

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    Nope, the clean channel should be quiet. How old are the tubes? How does it sound when playing?
     
  3. godwentpunk

    godwentpunk New Member

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    I'm sorry, I was not clear, the hiss is coming from my LEAD channel. The clean is pretty darn quite. I did get the amp used, it's under 2 years old but I can't say how many hours are on the tubes. The preAmps looks like JJ's and I'm not sure if those are stock or not.
     
  4. LSchefman

    LSchefman Hears Tones

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    I’d swap some tubes and see how that works. Hiss is mostly a tube thing. Lead channels usually employ an additional tube (or more than one).
     
  5. godwentpunk

    godwentpunk New Member

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    So you think it's a preamp issue versus a power tube?

    Joe
     
  6. LSchefman

    LSchefman Hears Tones

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    Most likely, since if it was a power tube it’d make noise on both channels.

    Have you tried tapping the tubes with a chopstick to see if you can find the possible culprit?
     
  7. godwentpunk

    godwentpunk New Member

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    The hiss is only on the CLEAN channel, the CLEAN sounds great. I've cleaned all of the tubes and that has not helped. I purchased an extra preamp tube and tried to put it in slot V1, V2 and V3 but nothing helped. My next option to get an entire new set of preamp tubes but that's over $100 for JJ's because this amp has 6 of them. I'm really stumped in this.

    Also, is the bias adjust slot the 1/4 cable looking slot on the bottom side of the chassis where the power tubes are located?

    joe...
     
    LSchefman likes this.
  8. LSchefman

    LSchefman Hears Tones

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    As I said because the noise is only on the clean channel, it’s not likely that it’s the power tubes, because the power tubes work on both channels.

    To find the bad tube, you should try the spare tube in all six spots, not just 3 of 6. You’ve only gotten halfway through! Just be patient, and go through them one at a time.

    Often you can find a microphonic tube quickly, by lightly tapping the preamp tubes with a wooden chopstick, or pencil, with the guitar/pedalboard disconnected, but the speaker connected and the amp turned on. It doesn’t have to be cranked up loud. Try it on both channels.

    You’ll hear the tapping clearly from V1 through the speaker, because it’s the initial gain stage of the amp, and unless it’s weird, don’t worry about it. The other tubes will tap a lot quieter, until you find the microphonic tube. That tube will be very sensitive to tapping and make the loudest noise through the speaker. If you find the bad tube that way, try the known good tube in it, and see if that helps.
     
  9. godwentpunk

    godwentpunk New Member

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    I promise that this is the last post from my phone that does auto correct. The hiss is on my LEAD channel only.

    I tried the first 3 positions with a new tube and in doing so, I've noticed I get strange results from v1. For example, with one tube, turning the volume knob eliminated some scratchiness but not the hiss.. I wonder if a have an issue with v1 tube holder...

    thanks for the input and suggestions.

    Joe
     

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