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  • 5e3 problems!!!!

    Hi there,

    I've some problems with my 5e3 build:

    All my voltages at my rectifier are ok , But I have the following problems:

    1 preamp & poweramp tubes don't fire up
    2 After the 1st resistor (5K) I measure 0 VDC, before the resistor I measure about 380 volts (which is o.k.)

    3 after a while the 5K resistor gets hot and almost burns down

    I think there's a problem with my Cap's.....But maybe some of you can explain what the exact problem is???

    Thanks ,,

    Tom

  • #2
    Take your ohmeter and measure resistance from 0v end of the 5K resistor to ground, what do you get? Sounds like you have a short.

    If you suspect the filter cap at this point, replace it.

    Comment


    • #3
      Hi Tom and welcome to the forum.
      380vdc before the 5K resistor is approximately what I would expect in a 5E3. After the resistor the voltage ought to be slightly less. No voltage here might as well be a broken (open) resistor.
      All the current drawn by the power tubes and preamp tubes goes through this resistor. Therefore it might get a little hot. What about the wattage you used? Should be at least 1W. If not, it might have burned up (being open then) before you measured the voltage.
      Next would be the question, why would it have burned up? Too much current draw? Check your wiring for a short as MWJB proposed and check the value of the power tubes cathode resistor.
      Hope this helps

      Comment


      • #4
        Hi there,

        The resistor isn't broken, I measured it => 5,1 kOhm it said, so that's ok. I can only measure this value with the amp turned off, is that normal?

        When I measure from 0 volt side to ground , i get 22K (which is the exact value of the second resistor in line)



        Thank in advance for all your help! It's my first diy amp as you can see

        Tom

        Comment


        • #5
          "I can only measure this value with the amp turned off, is that normal?" Yes.

          From the junction of the 5.1K and the 22K you have a wire running to pin 4 of the 6V6, confirm?

          You have the red wire from the OT connecting to the left most filter cap, or to rectifier pin 8, confirm?

          blue & brown wires from OT each run to one of the 6V6 pin 3, confirm?



          From the other end of the 22K you should read 0ohms to the junction of the 2x100K (brown/black/Yellow) resistors feeding pins 1 & 6 of the preamp tube (12AX7).

          How have you wired your heaters? Twisted pairs with a centre tap, twisted pair with 2x100ohm virtual centre tap resistors, or a single wire daisy chain?

          A picture is worth a thousand words, so please post some, might help us get to the bottom of this quicker.
          Last edited by MWJB; 01-18-2010, 02:16 PM.

          Comment


          • #6
            +1 I'd measure ohms from the preamp end on the second resistor (22k) to ground. Should NOT be zero ohms.

            Comment


            • #7
              Hello!

              I was wrong in my previous reply:

              When I measure resistance at my second cap (between the 5K and 22K resistor) to ground; I get 0 Ohm!

              I think I've to replace that cap.......

              Tommorrow I buy some new batteries for my digital camera so you all can have a look

              Thanks again so far

              Comment


              • #8
                Remove that cap, before you replace it, measure resistance again if you still get 0ohms look for shorts/stray blobs of solder shorting to ground.

                Comment

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