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pictures of my new amp build

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  • #31
    fyi, i found some old tubes at a shop down the street and plugged in a 12au7 as the power tube. WOW!
    the 12at7 sounded ok but compared to the 12au7, it sounded like an angry teenager armed with a bunch of distortion pedals.
    12au7 wins.
    in the preamp i tried a telefunken and a sylvania 12ax7 in place of the current production tung-sol. i didn't hear much difference. if it's there, it's subtle.

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    • #32
      Originally posted by yunger View Post
      it sounded like an angry teenager armed with a bunch of distortion pedals.
      LOL

      I did some math and found that your 12at7 was biased at 3.75 watts. So that would be a lot. And might be why the amp broke up so much. Could you take new voltage readings with the 12au7? I'd be interested.
      "Take two placebos, works twice as well." Enzo

      "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

      "If you're not interested in opinions and the experience of others, why even start a thread?
      You can't just expect consent." Helmholtz

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      • #33
        Originally posted by Chuck H View Post
        I did some math and found that your 12at7 was biased at 3.75 watts. So that would be a lot. And might be why the amp broke up so much. Could you take new voltage readings with the 12au7? I'd be interested.
        so: Plate Dissipation in Watts = (Plate Voltage - Cathode Voltage) x Plate Current.
        is plate current the same as cathode current? and cathode current is cathode volts/rk?

        btw, the 12at7 is rated for 2.5w per triode so in parallel 5w right?

        anyway here's the new voltages
        [ATTACH]16993[/ATTACH]
        Attached Files

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        • #34
          Originally posted by yunger View Post
          btw, the 12at7 is rated for 2.5w per triode so in parallel 5w right?
          Oh, right. I was figuring for the single triode dissapation.

          So you did change the cathode resistor? It looks to be 8.8 watts idle dissapation with the 12au7?!?
          "Take two placebos, works twice as well." Enzo

          "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

          "If you're not interested in opinions and the experience of others, why even start a thread?
          You can't just expect consent." Helmholtz

          Comment


          • #35
            Originally posted by Chuck H View Post
            So you did change the cathode resistor? It looks to be 8.8 watts idle dissapation with the 12au7?!?
            youre right. i went back to 470 rk and calculated 6.5w. maybe the tube can handle that until i can order some 510-620 resistors

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            • #36
              I had to join just to say that that's one nice amp (both of them, actually). I've been thinking about something similar for awhile now but I've got a few concerns that have kept me from doing anything yet. I want to use stainable wood and a front plate like yours but with a wooden grill design. How did you attach the front to the sides? Dowels? Biscuits? Is the front 3/4" thick? What are the dimensions of the cabinet, if you don't mind sharing?

              Thanks.

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              • #37
                Originally posted by Jack Sparrow View Post
                I had to join just to say that that's one nice amp (both of them, actually). I've been thinking about something similar for awhile now but I've got a few concerns that have kept me from doing anything yet. I want to use stainable wood and a front plate like yours but with a wooden grill design. How did you attach the front to the sides? Dowels? Biscuits? Is the front 3/4" thick? What are the dimensions of the cabinet, if you don't mind sharing?

                Thanks.
                thanks!
                -big amp is 20x18x11 3/4" pine, 1/2" ply baffle
                -little amp is 11x10x7 1/2" pine, 3/8" ply baffle
                if by plate you mean fascia, it's just 4 pieces cut at 45 degrees on end and glued inside the box in the final step of assembly. no need for dowels or biscuits...lateral loads are not a problem here.
                hope that helps.
                Last edited by yunger; 02-01-2012, 05:44 AM.

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                • #38
                  That makes sense. For some reason I assumed it was a frame of four pieces preassembled and attached to the front edges of the sides, top and bottom like a face frame on a kitchen cabinet.

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