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  • #16
    I created a small board layout for the regulator for the DC preamp heaters
    Click image for larger version

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    "UP here in the Canada we shoot things we don't understand"

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    • #17
      Check the data sheets on the pin-out of the three terminal regulators. The positive and negative versions do not have the same pin-out. They will need some kind of heat sink. This needs to be part of the layout.

      Check the size of the electrolytic caps you intend to use. They will likely be much larger than your layout shows.
      WARNING! Musical Instrument amplifiers contain lethal voltages and can retain them even when unplugged. Refer service to qualified personnel.
      REMEMBER: Everybody knows that smokin' ain't allowed in school !

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      • #18
        I was hoping on using the stock ic 7912 v& the 7812 along with the heat sinks ...i did have trouble sourcing them as an alternative in case the original's failed .
        According the the schematic no cap values no more than 25v .. I will run through the physical board itself . & let you know
        "UP here in the Canada we shoot things we don't understand"

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        • #19
          Using this amp as the basis ,I've decided to attempt to build a TrainWreck express using 2 5881 tubes for the power section & the DC heater circuit .
          My Question is about the full wave bridge as i have no center tap, In the Ashdown schematic ,I see there some small caps & a 220k resistor before the filter caps ,I guess this is necessary part of the Full wave bridge ?
          Here's the layout & schematic Click image for larger version

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ID:	847471 & the Ash down schematic Click image for larger version

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          Last edited by copperheadroads; 10-19-2017, 02:48 AM.
          "UP here in the Canada we shoot things we don't understand"

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          • #20
            Consider the 220K as a bleeder resistor (for first cap) and the 4n7 caps as noise suppression for the diodes.
            Neither are necessities or really part of a bridge, but both are useful additions.
            Originally posted by Enzo
            I have a sign in my shop that says, "Never think up reasons not to check something."


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            • #21
              It is unclear which 220K you are talking about. There is one that is part of the bias Voltage generator. That bias Voltage circuit won't work when a full wave bridge rectifier is used.
              WARNING! Musical Instrument amplifiers contain lethal voltages and can retain them even when unplugged. Refer service to qualified personnel.
              REMEMBER: Everybody knows that smokin' ain't allowed in school !

              Comment


              • #22
                Originally posted by loudthud View Post
                It is unclear which 220K you are talking about. There is one that is part of the bias Voltage generator. That bias Voltage circuit won't work when a full wave bridge rectifier is used.
                looks like R87 maybe just before (left) of the first 47uf filter cap
                "UP here in the Canada we shoot things we don't understand"

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                • #23
                  Yes, R87 is just a bleeder for the cap. But take note of what loudthud said, the bias circuit will not work with a bridge, you will have to find a different source for bias voltage. How does the Ashdown in your example do it?
                  Originally posted by Enzo
                  I have a sign in my shop that says, "Never think up reasons not to check something."


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                  • #24
                    Originally posted by loudthud View Post
                    There is one that is part of the bias Voltage generator. That bias Voltage circuit won't work when a full wave bridge rectifier is used.
                    what would we need to do ?
                    "UP here in the Canada we shoot things we don't understand"

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                    • #25
                      Originally posted by copperheadroads View Post
                      what would we need to do ?
                      Basically, you need a capacitor instead of the 220K. Here is an example, bias circuit is on page 2: http://el34world.com/charts/Schemati...0-02-iss14.pdf
                      WARNING! Musical Instrument amplifiers contain lethal voltages and can retain them even when unplugged. Refer service to qualified personnel.
                      REMEMBER: Everybody knows that smokin' ain't allowed in school !

                      Comment


                      • #26
                        Sorry I'm not seeing it in the schematic ,,I will do some more research .
                        "UP here in the Canada we shoot things we don't understand"

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                        • #27
                          Look at the D5 sector of the schematic (pg2). Cap is C12. WH point comes off the power transformer.
                          Originally posted by Enzo
                          I have a sign in my shop that says, "Never think up reasons not to check something."


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                          • #28
                            Thanks I did look at that
                            Wouldn't this be a similar schematic Click image for larger version

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                            At the bottom of the page
                            Capacitor Cupled Bias Supply
                            http://www.valvewizard.co.uk/bias.html
                            "UP here in the Canada we shoot things we don't understand"

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                            • #29
                              Yes, very similar. That will get you a bias supply without a CT in your HV winding.
                              Originally posted by Enzo
                              I have a sign in my shop that says, "Never think up reasons not to check something."


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                              • #30
                                Here's the Chassis , Click image for larger version

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                                My plan was to to cover larger holes that are towards the center & install my turret or eyelet board in that area & possibly drill holes (atleast one new hole ) for the power tubes , but I am not liking how close V1 will be to the Output transformer this build will have dc heaters on the preamp tubes . I wonder would if it be better if i move the OT up next to the power transformer , this is a combo amp but i think there is enough room to move the OT next to the PT .let me know what you guys think ?
                                "UP here in the Canada we shoot things we don't understand"

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