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  • Reached another wall on my tube amp project...

    I am building 5E4-A Fender Super Amp into an old Integrated amp chassis...its gonna be one heavy,HEAVY anp in a compact little package I have reached another one of thosemoments where I can't think of how to make this go forward. I am using a Magnetic Concepts power tranny for 18-20 watt that has this layout:

    http://classictone.net/40-18035.pdf

    The 5E4 is a fixed bias circuit if I'm not mistaken and Fender amps use a PT that has a seperate lead of the HT winding for the bias circuit. Can I still make this thing fixed bias or am I going to have to go cathode bias with this mama? Also I want to know how to lace in the B+ voltage.Do I just run a wire from pin 8 of the rectifier to the main filter? The way the schematics show this, is one 5volt lead goes to pin 2 then the other 5 volt lead goes straight to the main filter while jumper from pin 8 meets this one mid way.

    I am also wanting to know where the middle wire on my OT goes. On the front of it there are the two leads which go to the plates of the power tubes. The middle wire just shows it is, or goes to 8K ohms When looking at the schematic it seems that this lead also goes to the Filter circuit...hmmm, maybe to get power to the OT?...that only just came to mind. On the schematic it shows this wire also goes to the power tubes but does not specify which pin. I have been finding Fenders schematics very vague about such details when compared to schematics I have from Photofact folders on different amps.

    I hope this series of questions is clear, if not let me know and I will try to clarify.

    Thanks,Dan

    _____________________________-edit-_____________________________

    I figure it might be easier if I posted the schematic and layout, since I found them on the web for just such occasions!





    On another note, I am working with a pretty compact chassis and so was only going to use 2 inputs. Is it posseble to blend the two channels so that I can use the side of the 12ax7 that the second set of inputs would otherwise be using?
    Founder of the club. Dedicated to Rockin on and to fun at those who take themselves too seriously!!!

    Term limits for Congress. The true "Politics of Change"

    My rig:

    1991 HM Strat w/ Dimarzio X2N in the bridge, Chopper in the middle and Pro Track in the neck

    Gibson GA20RVT Late model

    Vox Tonelab LE
    EHX English Muff'n
    Morley Boost Wah, one of the old 110v ones

  • #2
    I am building 5E4-A Fender Super Amp into an old Integrated amp chassis...its gonna be one heavy,HEAVY anp in a compact little package I have reached another one of thosemoments where I can't think of how to make this go forward. I am using a Magnet Concepts power tranny for 18-20 watt that has this layout:

    http://classictone.net/40-18035.pdf

    The 5E4 is a fixed bias circuit if I'm not mistaken and Fender amps use a PT that has a seperate lead of the HT winding for the bias circuit. Can I still make this thing fixed bias or am I going to have to go cathode bias with this mama?



    All you have to do is pull the bias feed from one side of the mains. Take a look at the power supply in the last post in my winter amp thread... Just like that.


    Also I want to know how to lace in the B+ voltage.Do I just run a wire from pin 8 of the rectifier to the main filter?


    Yes that's all there is to it.


    The way the schematics show this, is one 5volt lead goes to pin 2 then the other 5 volt lead goes straight to the main filter while jumper from pin 8 meets this one mid way.



    The 5V rectifier heater wires go to pins 2 & 8, then from pin 8 to the first cap.



    I am also wanting to know where the middle wire on my OT goes. On the front of it there are the two leads which go to the plates of the power tubes. The middle wire just shows it is, or goes to 8K ohms When looking at the schematic it seems that this lead also goes to the Filter circuit...hmmm, maybe to get power to the OT?...that only just came to mind. On the schematic it shows this wire also goes to the power tubes but does not specify which pin. I have been finding Fenders schematics very vague about such details when compared to schematics I have from Photofact folders on different amps.


    The CT of the OT goes to your first power point in the supply, which is generally marked as "A". The other two wires go to pin 3 on the power tubes, that is your plates.



    I hope this series of questions is clear, if not let me know and I will try to clarify.

    Thanks,
    Dan
    Casey4sDIY Links:102 Amphttp://www.guitarkitbuilder.com/cont...-amplifier-kitChassis Layout:http://www.guitarkitbuilder.com/cont...lifier-chassisTurret Board:http://www.guitarkitbuilder.com/cont...d-construction Tolex Tutorial:http://www.guitarkitbuilder.com/cont...lifier-cabinet

    Comment


    • #3
      Here's a sketch for you on the bias supply

      Casey4sDIY Links:102 Amphttp://www.guitarkitbuilder.com/cont...-amplifier-kitChassis Layout:http://www.guitarkitbuilder.com/cont...lifier-chassisTurret Board:http://www.guitarkitbuilder.com/cont...d-construction Tolex Tutorial:http://www.guitarkitbuilder.com/cont...lifier-cabinet

      Comment


      • #4
        Casey handled the other questions, so I'll just focus on these two...

        On another note, I am working with a pretty compact chassis and so was only going to use 2 inputs. Is it posseble to blend the two channels so that I can use the side of the 12ax7 that the second set of inputs would otherwise be using?
        Yes. The easiest way of doing that is to pick one channel as being the default "blend" input, when nothing is connected to the other jack.

        For instance, if you pick channel 1 (top of the drawing) as being the "blend" or master input, you would connect the tip of that jack to the switched part of the input jack on the second (slave) input. When you only have a plug inserted in channel 1, both inputs are in parallel. Both volume controls will affect the same signal plugged into channel 1.

        But when you insert a plug into channel 2, both channels will be independent. If you only have something plugged into channel 2, only the bottom volume control will do anything. If you also connect another guitar into channel 1, each guitar will have its own volume control on the amp.


        Or you can wire it so channel 2 is the master (blend) and channel 1 is the "slave". Whichever you prefer.
        Originally Posted by Anderton


        FYI God posts here, but under an alt.









        Originally Posted by BernardAlbrecht


        Yeah, it's SomeoneYouKnew.



        Apparently I'm God.

        Comment


        • #5
          The Deluxe 6G3 schematic shows a similar bias supply off of one of the mains similar to my drawing, but without the adjustment pot.

          http://www.el34world.com/charts/Schematics/files/fender/deluxe_6g3_schem.pdf

          EDIT, change the dropping resistor from 82K to 100K if the -Voltage is too high.
          Casey4sDIY Links:102 Amphttp://www.guitarkitbuilder.com/cont...-amplifier-kitChassis Layout:http://www.guitarkitbuilder.com/cont...lifier-chassisTurret Board:http://www.guitarkitbuilder.com/cont...d-construction Tolex Tutorial:http://www.guitarkitbuilder.com/cont...lifier-cabinet

          Comment


          • #6
            SYK,

            I was thinking about your answer above and I have a question. Do you still share the cathode bias like the original schematic? I can't see why not unless you wanted to "voice" the cathodes differently, which might be intresting.
            Casey4sDIY Links:102 Amphttp://www.guitarkitbuilder.com/cont...-amplifier-kitChassis Layout:http://www.guitarkitbuilder.com/cont...lifier-chassisTurret Board:http://www.guitarkitbuilder.com/cont...d-construction Tolex Tutorial:http://www.guitarkitbuilder.com/cont...lifier-cabinet

            Comment


            • #7
              Casey handled the other questions, so I'll just focus on these two...

              The CT of your OT connects to the B+ after the choke and also to the screen grids of both 6V6s (pin 4)

              .


              Thank you, the schematic showed it going to the power tubes but didn't specify which pin. Also concerning the choke, I only just realized that there is suppossed to be a choke hereI know chokes come in all manner of strengths, how would I go about findingthe proper choke for this application? I happen to have an 85 ohm/1500V that has been in lying around.


              And thanks Casey for the info as well.
              Founder of the club. Dedicated to Rockin on and to fun at those who take themselves too seriously!!!

              Term limits for Congress. The true "Politics of Change"

              My rig:

              1991 HM Strat w/ Dimarzio X2N in the bridge, Chopper in the middle and Pro Track in the neck

              Gibson GA20RVT Late model

              Vox Tonelab LE
              EHX English Muff'n
              Morley Boost Wah, one of the old 110v ones

              Comment


              • #8
                Use the basic Fender choke right there, it's 4 Henries and 108 ohms. The Fender part number is 125C1A and is about $13.00 at AES.

                http://www.tubesandmore.com/
                Casey4sDIY Links:102 Amphttp://www.guitarkitbuilder.com/cont...-amplifier-kitChassis Layout:http://www.guitarkitbuilder.com/cont...lifier-chassisTurret Board:http://www.guitarkitbuilder.com/cont...d-construction Tolex Tutorial:http://www.guitarkitbuilder.com/cont...lifier-cabinet

                Comment


                • #9
                  Thank you, the schematic showed it going to the power tubes but didn't specify which pin. Also concerning the choke, I only just realized that there is suppossed to be a choke hereI know chokes come in all manner of strengths, how would I go about findingthe proper choke for this application? I happen to have an 85 ohm/1500V that has been in lying around.


                  And thanks Casey for the info as well.
                  I found the pin number for the screens by comparing the schematic to the layout drawing.

                  You don't absolutely have to have the choke, but it will smooth things out a ton more than just using a 100 ohm resistor. I see Casey has a source for you. I guess we're tag-teaming this one.

                  Here, have a couple of drawings. You can probably reason out what's happening with the inputs, but don't hesitate to ask, if there is anything that isn't crystal clear.



                  Originally Posted by Anderton


                  FYI God posts here, but under an alt.









                  Originally Posted by BernardAlbrecht


                  Yeah, it's SomeoneYouKnew.



                  Apparently I'm God.

                  Comment


                  • #10
                    One of the problems with running the two channels, is the fact that I'm working with such a compact chassis. I only have enough room on the face for the Prescence, Bass,Treble, and Volume pots. In fact I am using a On/Off/1M pot so I can keep the on switch on the front of the amp. In fact the pilot light is sitting just a cunt hair over the rectifier socket. I have the Standby switch on the back next to the fuse, so I figured if I can just make it a one input amp and use the rest of that preamp tube for an additional gain stage for the 1st channel. In fact its so cramped that I mounted the filter caps over the OT with a set of 8 lug terminal strips, and the bias board is mounted on the side of the chassis leaving enough room to utilize the original amps hum control as a bias pot

                    This is how much room I'm working with:



                    I have another pot mounted in the extra input hole because I am thinking on adding a master volume...after I have it working and all the bugs worked out...

                    I left the wires of the PT long only for the time being. On the off chance I want to go with another PT later, I'd like to have enough leads left to still use this PT in a Marshall clone later on.
                    Founder of the club. Dedicated to Rockin on and to fun at those who take themselves too seriously!!!

                    Term limits for Congress. The true "Politics of Change"

                    My rig:

                    1991 HM Strat w/ Dimarzio X2N in the bridge, Chopper in the middle and Pro Track in the neck

                    Gibson GA20RVT Late model

                    Vox Tonelab LE
                    EHX English Muff'n
                    Morley Boost Wah, one of the old 110v ones

                    Comment


                    • #11
                      so I figured if I can just make it a one input amp and use the rest of that preamp tube for an additional gain stage for the 1st channel.
                      I think i see where you're headed with this. You don't want to "blend" the paralleled triodes. You want to cascade one into the other, right?

                      Like maybe have the first channel feeding the second for additional gain. Or plug into the second channel instead, and that bypasses the first channel completely for normal gain?
                      Originally Posted by Anderton


                      FYI God posts here, but under an alt.









                      Originally Posted by BernardAlbrecht


                      Yeah, it's SomeoneYouKnew.



                      Apparently I'm God.

                      Comment


                      • #12
                        Basically just have a single channel amp, and use the leftover triodes for gainstages...or, Iguess gain stage would be more to the point as it looks like that second channel is only using one side of the last 12ax7



                        Would an 85 ohm choke work?
                        Founder of the club. Dedicated to Rockin on and to fun at those who take themselves too seriously!!!

                        Term limits for Congress. The true "Politics of Change"

                        My rig:

                        1991 HM Strat w/ Dimarzio X2N in the bridge, Chopper in the middle and Pro Track in the neck

                        Gibson GA20RVT Late model

                        Vox Tonelab LE
                        EHX English Muff'n
                        Morley Boost Wah, one of the old 110v ones

                        Comment


                        • #13
                          Wow, that really is a compact chassis
                          DCC Engineering. Custom Cabs and Effects.






                          Originally Posted by -Assy-


                          Okay I summed up this entire thread in three posts. Let's go home and beat our children.

                          Comment


                          • #14
                            Would an 85 ohm choke work?
                            yeah. it won't drop as much voltage so your B+ will be a few volts higher. dunno what the inductance of your choke is or what it should be. more inductance will do a better job of filtering. if your choke can handle the current requirements, you should be okay. everything is going through the choke on this amp, even the plate supply. so it might be about 100 mA total.
                            Originally Posted by Anderton


                            FYI God posts here, but under an alt.









                            Originally Posted by BernardAlbrecht


                            Yeah, it's SomeoneYouKnew.



                            Apparently I'm God.

                            Comment


                            • #15
                              Eh...I'll just go ahead an get choke through one of the on line parts houses. At the point that I am now even if I were to finish this amp today I would still be waiting to fire it up. My variac I got used and it was missing the guts inside the receptacle. I finally found the part for it through mouser.com and have to wait til the 1st to get it, so might as well do it right I haven't skimped anywhere on this build yet and it seems that would be a poor place to start.

                              Wow, that really is a compact chassis


                              Yeah, and it weighs a ton!!! I'm using a big peice of iron for the OT...For a Marshall 45watt JTM I was looking all oevr for an older style OT with closed bells and 4 point mount, then I ran across this one and thought...**************** it close enough to the existing bolt pattern to rock it for me. When I first started this project last year it was goingto be a Marshall 18 watt clone.
                              Founder of the club. Dedicated to Rockin on and to fun at those who take themselves too seriously!!!

                              Term limits for Congress. The true "Politics of Change"

                              My rig:

                              1991 HM Strat w/ Dimarzio X2N in the bridge, Chopper in the middle and Pro Track in the neck

                              Gibson GA20RVT Late model

                              Vox Tonelab LE
                              EHX English Muff'n
                              Morley Boost Wah, one of the old 110v ones

                              Comment



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