Announcement

Collapse
No announcement yet.

Hiwatt dr103 Bias voltage to little

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Hiwatt dr103 Bias voltage to little

    So I have a stock 70's DR103 with the bias voltage AC appx 356v. Its very anemic. I can get the new el34's to about 36ma at 503v DC with a bias pot added. But, I would like to see it around 30-32ma, not as hot.

  • #2
    Not sure what you mean about the bias circuit AC being 356V? Does it not have the bias winding?
    Here is the bias circuit with pot added from Mark Huss's site


    Click image for larger version

Name:	bias.gif
Views:	1
Size:	10.4 KB
ID:	852722
    Originally posted by Enzo
    I have a sign in my shop that says, "Never think up reasons not to check something."


    Comment


    • #3
      Yeah for Hiwatt and Sound City amps this is common.

      Google search for "Hiwatt bias doubler" to find a schematic to double the bias voltage.

      Comment


      • #4
        Originally posted by g1 View Post
        Not sure what you mean about the bias circuit AC being 356V? Does it not have the bias winding?
        Here is the bias circuit with pot added from Mark Huss's site


        [ATTACH=CONFIG]51947[/ATTACH]


        Im sorry 36v ac.

        Comment


        • #5
          Here's a couple: (single and dual control)
          https://hiwatt.org/Schematics/BiasCkts2.gif
          Originally posted by Enzo
          I have a sign in my shop that says, "Never think up reasons not to check something."


          Comment


          • #6
            Sure, you could build a doubler- no arguement. I have to wonder if you couldn't hit the goal with a simple resistor change or two, though.
            "I took a photo of my ohm meter... It didn't help." Enzo 8/20/22

            Comment


            • #7
              Originally posted by The Dude View Post
              Sure, you could build a doubler- no arguement. I have to wonder if you couldn't hit the goal with a simple resistor change or two, though.
              I know, IT sucks to have to add extra parts. I just need to cool it down a bit more from avg 36ma per tube to 32ma. I get 36v ac on the other side of the diode. Strange how little there is on tap!

              Thanks for the link

              Comment


              • #8
                What is the VDC at the anode end of the diode?
                Originally posted by Enzo
                I have a sign in my shop that says, "Never think up reasons not to check something."


                Comment


                • #9
                  Originally posted by g1 View Post
                  What is the VDC at the anode end of the diode?
                  Appx 36vdc. plates are appx 503v, I hope these new 34's can handle it.

                  Comment


                  • #10
                    Have you tried replacing the cap there? I think you should get more than 36VDC with 36VAC going to the diode.
                    Originally posted by Enzo
                    I have a sign in my shop that says, "Never think up reasons not to check something."


                    Comment


                    • #11
                      ^^^^^^ I agree. I might also try upping the value of the 47k across the cap. I don't think you need a large increase in bias voltage to get to 30-32mA bias.
                      "I took a photo of my ohm meter... It didn't help." Enzo 8/20/22

                      Comment


                      • #12
                        Originally posted by The Dude View Post
                        ^^^^^^ I agree. I might also try upping the value of the 47k across the cap. I don't think you need a large increase in bias voltage to get to 30-32mA bias.
                        It was stock 100uf cap 47k giving about 48ma cooking per tube at 510v. I put a small 25k trim pot and changed the 47k to a 100k and it got me to appx 36ma per tube 503 plate but its still too hot. I have left the 100uf stock cap in there. So you suggest changing it?

                        Comment


                        • #13
                          If the cap is bad or starting to go bad it can drag the bias voltage down.

                          Plus if it shorts or does go bad it can do alot of damage.

                          Bias supply filters are very important.

                          Comment


                          • #14
                            I'd try either changing it, or temporarily clipping another one across it to see if anything changes.
                            "I took a photo of my ohm meter... It didn't help." Enzo 8/20/22

                            Comment


                            • #15
                              "I'd try either changing it, or temporarily clipping another one across it to see if anything changes."

                              Yeah, but if the cap is partially shorting and pulling the voltage, what will clipping in another across it tell us?
                              It's weird, because it WAS working fine.....

                              Comment

                              Working...
                              X