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weber java issues...please help

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  • weber java issues...please help

    picked this as my first build, i wanted the challenge. i have voltages that are too high to some of the caps and to the tubes. el-34's that shipped with the amp can only manage 0.6ma of bias current. swapped for 5881's and can get to 13ma. with el-34s, no noise at all from amp. no hums, buzzes, farts, etc. installing the 5881's gets me no sound, but i do get some hum with the MV and volume WFO. where to next?

  • #2
    I don't think there's enough info there, but here's a start for stuff any helper might want to know:
    What is your bias voltage?
    How are you measuring idle current?
    How do you have the screen grid resistors and power tube grid stoppers mounted? On the socket? Describe exactly how/where they are mounted.

    Voltages throughout the amp would be helpful.

    Comment


    • #3
      And when you decided on EL34s, did you add a wire from pin 1 to pin 8 on the sockets for them? 6L6 does not use pin 1, so in fact we often use pin 1 as a handy wiring point for other parts. EL34 DOES use pin 1. it is the suppressor grid and wants to be connected to the cathode - those are pins 1 and 8 on each EL34.

      The only tube voltage readings at all meaningful will be ones with ALL the tube installed.
      Education is what you're left with after you have forgotten what you have learned.

      Comment


      • #4
        sorry, should have posted voltages yesterday. now it has sound, only have 15.6ma for bias with it maxed on 5881's. voltages are to ground as follows.
        refer to layout for lettered positions
        https://taweber.powweb.com/store/java_layout.jpg

        filter caps are all ~250-245 Vdc
        coupling caps - B. 489 C. 453 D. 438 E. 428

        V1 - 1. 187 2. 0(caused interference) 3. 1.3 6. 227 7. 187 8. 185
        V2 - 1. 171 2. 0 3. 1.5 6. 242 7. HUM 8. 2.72
        V3 - 1. 255 2. 76 3. 117 6. 237 7. 80 8. 117
        pins 4,5, and 9 all are 3.15Vac
        V4 - 1. 0 3. 489 4. 490 5. -55 6. 490 8. 0
        V5 - 1. 0 3. 489 4. 490 5. -55 6. 490 8. 0
        pins 2,7 - 3.15Vac

        bias rite reads 489V and 15.6ma with bias pot maxed.

        i know voltage is a little high on V3 pin 1. i need to change to lower voltage taps on PT to get cap voltages down below the rated voltage. hoping it will drop that voltage enough to. amp has barely any output and really nasty distortion with everything maxed out.

        Comment


        • #5
          Looks like your screen voltage is higher than your plate voltage which doesn't seem right...especially since you have a 1K resistor instead of a choke. It's just barely higher...I'm not sure how much of a problem that is but it just looks like it should be a good 10vdc-15vdc lower just because you're using a 1K resistor as a choke.

          I would triple check your wiring around there. BTW - those 100uF caps are in series and those 220K resistors in parallel are balancing resistors (to ensure that exactly half the supply voltage is across each cap). So if those 100uF filter caps are rated at 250vdc then when in series (with balancing resistors) they're good to 500vdc.

          Also - those 20uF caps (B, C, D, and E) are all filter caps not coupling caps. They just filter each B+ node for the phase inverter and preamp triodes. The coupling caps are like the .1uF caps in phase inverter.

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