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  • #16
    Originally posted by ernest View Post
    I'm confused on how to determine what Ohm speaker to use with this transformer that came with my parts amp. How do you tell?...
    Usually I check unknown OTs by running a 1V Ac signal through and check the turns ratio. That will let you know for what speaker the OT was intended for and give you pointers as to how you can use it. Be careful, don't shock yourself. Search for testing unknown output transformers e.g.:
    Finding Unknown Values for Output Transformers
    The other thing I would want to be sure about is: do I have a single ended or a push pull transformer? Pretty sure you have a push pull, but SE OTs with parallel output tubes are not unknown.
    Hope this points you a bit in the right direction.

    Comment


    • #17
      Originally posted by overtone View Post
      Usually I check unknown OTs by running a 1V Ac signal through and check the turns ratio. That will let you know for what speaker the OT was intended for and give you pointers as to how you can use it.
      The other thing I would want to be sure about is: do I have a single ended or a push pull transformer? Pretty sure you have a push pull, but SE OTs with parallel output tubes are not unknown.
      Hope this points you a bit in the right direction.
      Yes, best answer I've gotten so far. not sure what any of it means yet but a definite starting point.

      thanks!

      Comment


      • #18
        He just means, put a small AC voltage into the secondary winding... measure across the full primary winding ... divide the small number into the big number... take that new number and square it...
        Then multiply that sq'd number by the speaker load impedance (4 ohm, 8ohm etc) and you have the primary impedance.
        EX:
        6vac into the secondary wires... measure the primary wires at say 180vac. Oh and that will knock you on your ass.
        180v divided by 6v = 30 a 30:1 voltage ratio
        30^2 or 30x30 = 900
        900 x 8 ohm speaker = 7200 ohms
        900 x 4 ohm speaker = 3600 ohms

        etc
        Bruce

        Mission Amps
        Denver, CO. 80022
        www.missionamps.com
        303-955-2412

        Comment


        • #19
          Originally posted by Bruce / Mission Amps View Post
          He just means, put a small AC voltage into the secondary winding... measure across the full primary winding ... divide the small number into the big number... take that new number and square it...
          Then multiply that sq'd number by the speaker load impedance (4 ohm, 8ohm etc) and you have the primary impedance.
          EX:
          6vac into the secondary wires... measure the primary wires at say 180vac. Oh and that will knock you on your ass.
          180v divided by 6v = 30 a 30:1 voltage ratio
          30^2 or 30x30 = 900
          900 x 8 ohm speaker = 7200 ohms
          900 x 4 ohm speaker = 3600 ohms

          etc
          cool thanks man, I also have it narrowed down by finding someone online using the same ampro amp as his setup.
          http://www.talkbass.com/forum/f15/am...intage-826548/

          without a doubt he confirmed that his which looks damned identical, came with a 16 ohm speaker.

          Comment


          • #20
            cabinet

            I fit some tan naugahyde to my cabinet over the weekend. 3m super 77 adhesive. I run a graphics dept for a print shop so I have access to the adhesive as well as full run of the maintenence shop where I'm building the chassis. I think it turned out great.

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            • #21
              so, decided on a speaker. I didn't have a lot to spend on a speaker at least not right now. I've already given a big chunk to the resistors, caps, knobs, jacks, etc....so I had to save on the speaker...for now.
              so many options, AlNico/ceramic, watt, ohm, so I would love to have a celestion blue, tone tubby, or something like that, I almost went with an old organ speaker with square alnico mag. What I ended up with was very affordable, a celestion G12 that has a modified aluminum voice coil and Hemp cone. I like a bass and mid with early breakup so I hope I'll be happy with it.

              and a oxblood grill.

              Comment


              • #22
                This chassis is kickin my ass. blew a hole through it with a welder so I'm going to have to make some sides and pop rivet them instead.


                Comment


                • #23

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                  • #24
                    Hmm .. the eyelet circuit board appears to have the B+ rail grounded side on the wrong side of the board with respect to the chassis...
                    Bruce

                    Mission Amps
                    Denver, CO. 80022
                    www.missionamps.com
                    303-955-2412

                    Comment


                    • #25
                      Originally posted by Bruce / Mission Amps View Post
                      Hmm .. the eyelet circuit board appears to have the B+ rail grounded side on the wrong side of the board with respect to the chassis...
                      I don't have the board entirely wired yet. doing the best i can with the links below.

                      thanks

                      Parts list

                      schematic #1

                      schematic #2

                      Comment


                      • #26
                        #2 artwork:
                        Doug might be doing that on purpose for some reason... other then just to be different (guess that's OK) I don't know why.
                        Bruce

                        Mission Amps
                        Denver, CO. 80022
                        www.missionamps.com
                        303-955-2412

                        Comment


                        • #27
                          Originally posted by Bruce / Mission Amps View Post
                          #2 artwork:
                          Doug might be doing that on purpose for some reason... other then just to be different (guess that's OK) I don't know why.
                          Bruce, I think I may have picked a board style that requires a bit more background knowledge than I have for my first project. I can read how the caps and resistors are populated to the board just fine but now I'm getting into how this wires into the input and output jacks and this was left a bit vague on Hoffmans schematic....I'm sure it's all on his site somewhere though.

                          that and I'm using old trannys with extra wires that I don't know what to do with. for instance I have six wires coming out of my output tranny, yet I can only find three on all the schematics.

                          Still trying to figure out where I star ground all of this as well. just pick a bolt on the chassis and connect all my grounds to it?

                          two unaccounted wires on the PT as well, a brown one and a bare wire?

                          Comment


                          • #28
                            Originally posted by ernest View Post
                            ....I'm sure it's all on his site somewhere though.
                            just gota look...

                            Instructions

                            Comment


                            • #29
                              cont...5e3 first build by Ernest - Hoffman Ampifiers Guitar Tube amp forum

                              at Hoffman's site so I can wrap this up.

                              thanks

                              Comment


                              • #30
                                finished...here

                                5e3 first build _ampro - Hoffman Ampifiers Guitar Tube amp forum

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