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  • Valve /tube amp noises

    Hi folks

    Organ amps can make frying bacon sounds, white noise, pink noise, rustling, shooting.... Many random noises

    I'm working on the 3 channel valve amp in an H, and have all of the above at times.

    Ive heard valves can be swapped to check and that carbon old resistors can impart noise

    Any other ideas?

  • #2
    Carbon composition resistors can cause noise in certain circuit positions, like plate load resistors. In other positions, with no DC current across them, they are not noises sources.

    Tracking down noise is a process of isolation. Determine where the noise is NOT coming from.

    The H-100 also has transistors in it, and early transistor circuits can be sources of hiss from the transistors themselves or from base biasing resistors, which tubes generally don't need.

    I'm David. 'Dave' is someone else's name.

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    • #3
      When I service an H-100 I change ALL plate load and screen grid resistors. Also, all E caps.

      Geo

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      • #4
        Hi folks

        Please help me identify where the plate load resistors are

        I have schematic but I'm not very conversant with valve tube theory

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        • #5
          R357, R358, R364, R384, R385, R391, R112, R113, R416.
          C332, C339, C350, C356, C366,
          C704, C705 (Bias supply)

          Geo

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          • #6
            It's an unpopular opinion, but if you don't know what a plate load resistor is, you probably shouldn't be working on tube amps. We get people on this forum every week who try to fix their own gear, make mistakes because they don't understand what they're doing, and then ask us to help them figure out what they did wrong.

            Tube amp technology is 100 years old at this point. Everything about it is well-documented and easily available on many websites. It is easier to educate yourself on how it works than at any time in history.

            https://robrobinette.com/How_Tubes_Work.htm
            I'm David. 'Dave' is someone else's name.

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            • peterb_2795
              peterb_2795 commented
              Editing a comment
              That is an excellent link with clear, lucid explanations. Thank you for posting.

          • #7
            David, my background is in electronic engineering, but I'm too young to have studied this

            It's an easy question.... Just keen to understand more

            Besides, here in the uk there is basically no one with any ability or interest in working on an H100!

            Don't worry... I'll be safe. Might make a mistake, true. But I'll be wiser


            ‚Äč

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            • #8
              ... Just been reading your link. Its excellent... Thanks

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              • #9
                Anyone else with any thoughts on letting the h100 noise floor ?

                I've now replaced all the 1uf and 0.1uf coupling capacitors which has reduced hum considerably

                And added 1000uf electrolytic on each transistor preamp board power rails. Dramatic, but every one reduced hum further.

                Still have a background hum not controlled by expression pedal, so probably more smoothing for main amps

                Still got some carbon plate resistors to swap. Interestingly, some have been done befor , which suggests failure. Those which remain are in tolerance , but I appreciate introduce noises.

                The reverb channel when energised has shooting noises....

                Any further help gratefully received...

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