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Harmony H415 amp

Discussion in 'Glowing Bottle Tube Amp Forum' started by bluerolo, Dec 5, 2020.

  1. bluerolo

    bluerolo TDPRI Member

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    View attachment 793191 Hi all, hoping for a bit of help on my new favorite amp, these Harmony H415 amps are just amazing, out of the box they are a bit light on gigging volume, but a pair of higher efficiency View attachment 793191 speakers makes a world of difference. The mic channel, input 4, is significantly hotter...I'm hoping someone can tell me which components on the attached schematic to replace so I can make channel 1 as hot as the mic...
    harmony_415.gif
     
  2. gusfinley

    gusfinley Tele-Afflicted

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    From what I can tell, It looks like the cathode of the Channel 4 gain stage (pin 3) is grounded (no cathode resistor).
     
  3. bluerolo

    bluerolo TDPRI Member

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    Thx Gus I see, so would it be R6 to remove and put to ground? Then I'm also wondering about R5 at 390K and R7 at 2.7M...does the 390K need to go to 2.7M?
     
  4. NTC

    NTC Tele-Meister

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    I'm not Gus, but yes. That triode won't work if you remove the cathode resistor and don't have a large resistor on tge grid to ground. It is called grid-leak biasing. Amps from the 1940's and early 1950's are biased this way.
     
  5. bluerolo

    bluerolo TDPRI Member

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    Thx for your help also NTC, not sure then what exactly you were saying needs to be done...to get channel 1 to be equivalent to the mic channel 4?
     
  6. NTC

    NTC Tele-Meister

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    Yes, just copy the one you like.
     
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