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  • #31
    http://ax84.com/

    These guys are all incredibly helpful.

    Unless you enjoy a bunch of yahoos telling you not to do what you are asking for help doing.

    Aren't they always SUCH a big help?

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    • #32
      Originally posted by gusfinley


      Yeah, this schematic still makes me dizzy!! I've got it about 70% figured out.... I removed capr C92, i think - the one between the tonestack and the cathode in the cathode follower circuit - BIG difference - at least on the clean channel..

      The other filtering may be there to compensate for the lack of negative feedback in the amp... I'lll have to check out the schematic again and look for the shunt caps on the plate load resistors.....

      this has become quite the good discussion!!!

      Keep it coming!!


      C92, I guess you jumped a wire across the space left over otherwise the tone stacks would not work. C92(630Volts) would block the DCV allowing C106, 107 & C108 to be low voltage caps(50-63V) and cheaper in cost.
      You may run the risk of burning out C106, 107 and 108 unless you replace them with a higher voltage, otherwise the removal of C92 is fine. I would go 400V to be super safe.

      Comment


      • #33
        I was looking the schematic over today and its looks like that C92 is part of the switching circuit - by removing it, I think that I am now running the signal through TWO tonestacks... This may explain why the bass is HUGE on the clean channel, but doesn't have the same effect on the OD channel, because it is only running though one tone stack.

        I'm not sure if that is right, but it looked right to me earlier. I'll be place pin terminals in the places I'll be removing changing parts, so that I can do some on the fly modding, I'll have to see what this cap really is doing tone-wise and then I'll post the results hopfully within a week.... I don't think it is doing hardly anything for the distortion channel........

        I'm gathering all sorts of good info for my upcoming Marshall DSL401 page, that I am planning, along with thoughts on speakers/ impedance matching, and even some perspectives on AC30 tone "secrets" that I may have stumbled across.... If I only have another day in the week I could get this all done!!

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        • #34
          That cap just feeds the tone stack and blocks any DC from reaching the lower voltage caps. If you did not put in a jumper that would explain your problem with the bass etc. BUT if you do put in a jumper please note my warning about the other caps. You will be hitting them with about 150V, and they are only designed for 63 and 50. Replace with at least 250V caps or even better 400. You could just put the blocking cap back in It has a purpose. Maybe try a larger value if you want more bass, like .2 mfd. This cap should not effect your treble! Is it a good quality orange drop?

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          • #35
            "Maybe try a larger value if you want more bass, like .2 mfd. This cap should not effect your treble! Is it a good quality orange drop?"

            it looks like an orange drop, but its more redish than orange...

            by the way when you say mfd are you talking microFarads. The appropriate abreviation for micro is u, because m is milli. This is a common mistake I see with people who work on guitar amp - it really confuses me!! It would be better to type out microF than use mF is you are uncomfortable using uF....

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            • #36
              Originally posted by gusfinley
              "Maybe try a larger value if you want more bass, like .2 mfd. This cap should not effect your treble! Is it a good quality orange drop?"

              it looks like an orange drop, but its more redish than orange...

              by the way when you say mfd are you talking microFarads. The appropriate abreviation for micro is u, because m is milli. This is a common mistake I see with people who work on guitar amp - it really confuses me!! It would be better to type out microF than use mF is you are uncomfortable using uF....


              I am just old school and that is how I was taught, mfd is very common and still in use. Just check the way your electrolytic caps are labeled. Sorry if it throws you off. Same thing with pF aka mmfd. So how is the amp coming?

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              • #37
                I haven't had any time to work on the amp - TOO much homework!! - also I have parts coming in the mail... so its kind of conveniant... I can't be distracted by playing my amp - It still works and all, but I might as well track down the open circuits and install all the "header" terminals all at the same time, so I'm holding out on that until the parts arrive....

                I wish I would known about the different cap vaules earlier!! I could have ordered a .2uF with all my other parts!! It sucks to have to pay more in shipping than you pay for a component.....

                Comment


                • #38
                  Originally posted by gusfinley
                  I haven't had any time to work on the amp - TOO much homework!! - also I have parts coming in the mail... so its kind of conveniant... I can't be distracted by playing my amp - It still works and all, but I might as well track down the open circuits and install all the "header" terminals all at the same time, so I'm holding out on that until the parts arrive....

                  I wish I would known about the different cap vaules earlier!! I could have ordered a .2uF with all my other parts!! It sucks to have to pay more in shipping than you pay for a component.....


                  Haha, well stick to the homework and maybe you'll be advising me someday I never order through the mail. What city are you in? There must be some electronic parts dealers close to you! Check the phone book for Electronic parts or components, wholesale/retail. Most wholesale guys will sell over the counter if you ask nicely.

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                  • #39
                    other than radio shack and the university enginnering parts store there are no places I have found that have the kinds of part I need.

                    Usually just telling them what I need confuses them... "what is logarithmic taper potentiometer?" "What is a wire-wound power resisitor?"

                    I'm sure they get sick of me because they either don't have what I am looking for or they don't have the "right" kind - try telling them that you only want a ceramic cap instead of an electrolytic - it doesn't go over to well.. or try telling them why you need a cap rated for 500V+....

                    I'm about 100 miles from Salt Lake City... in a little valley - so even driving there to get parts isn't going to work!!

                    its too bad really.....

                    Comment


                    • #40
                      Originally posted by gusfinley
                      other than radio shack and the university enginnering parts store there are no places I have found that have the kinds of part I need.

                      Usually just telling them what I need confuses them... "what is logarithmic taper potentiometer?" "What is a wire-wound power resisitor?"

                      I'm sure they get sick of me because they either don't have what I am looking for or they don't have the "right" kind - try telling them that you only want a ceramic cap instead of an electrolytic - it doesn't go over to well.. or try telling them why you need a cap rated for 500V+....

                      I'm about 100 miles from Salt Lake City... in a little valley - so even driving there to get parts isn't going to work!!

                      its too bad really.....


                      Well living in a little valley I am sure has it's advantages. Like at least cleaner air! I know what you mean though, it is hard to get some parts. Try finding all the local instrunent repair guys, in SLC. You may get lucky and find a tube teck that will help you out with hard to find stuff. Like I get JJ caps 50/50@500WV off a local guy for $6. I don't even know what they sell for on line

                      Comment


                      • #41
                        Here's a few books for you to keep an eye out for...

                        Electric Guitar Amplifier Handbook, 2nd edition - Jack Darr. Published by Howard W. Sams & Co., Inc.

                        Fundamentals Of Vacuum Tubes, 2nd Edition - Austin V. Eastman. Published by McGraw-Hill Book Company, Inc., 1941.

                        Noise Reduction Techniques In Electronic Systems- Henry W. Ott. Published by John Wiley & Sons, 1976.

                        Principles of Electronics - M. R. Gavin and J. E. Houldin. Published by D. Van Nostrand Company, Inc., 1959.

                        Principles of Electron Tubes - Herbert J. Reich. Reprint published by Audio Amateur Press, 1995.

                        Valve Amplifiers - Morgan Jones. Published by Newnes, Butterworth-Heinemann, Ltd. 1995.

                        A Desktop Reference of Hip Vintage Guitar Amps - Gerald Weber. Published by Kendrick Books, 1994.

                        Audio Cyclopedia, 2nd Edition - Howard Tremaine. Published by Howard W. Sams & Co., Inc. The Bobbs-Merrill Co. Inc., 1974.

                        Audio Transformer Design Manual - Robert G. Wolpert. 1989. http://www.rgwdesign.com

                        Build Your Own Audio Valve Amplifiers - Rainer zur Linde. Published by Elektor Electronics, 1995.

                        Dave Funk's Tube Amp Workbook - Dave Funk. Published by Thunderfunk Labs, Inc. 1996.

                        Comment


                        • #42
                          Originally posted by guitarzan


                          Well living in a little valley I am sure has it's advantages. Like at least cleaner air! .....Like I get JJ caps 50/50@500WV off a local guy for $6. I don't even know what they sell for on line


                          Funny you mention air quality... I live in a little valley and there are TONS of cows - so many in fact that "methane emissions" relatating to cows cause 60% of the air pollution!! When we get inversions they don't let the kids go outside at school because the air gets worse than L.A.!! Its kinda wierd.... They tell us to stop driving, but the big problem in the cows!!

                          J.J. 50-50s go for about 8-9 online, so you are saving a few bucks...

                          Comment


                          • #43
                            Originally posted by guitarzan
                            Here's a few books for you to keep an eye out for...

                            Fundamentals Of Vacuum Tubes, 2nd Edition - Austin V. Eastman. Published by McGraw-Hill Book Company, Inc., 1941.

                            Principles of Electronics - M. R. Gavin and J. E. Houldin. Published by D. Van Nostrand Company, Inc., 1959.

                            Principles of Electron Tubes - Herbert J. Reich. Reprint published by Audio Amateur Press, 1995.

                            Valve Amplifiers - Morgan Jones. Published by Newnes, Butterworth-Heinemann, Ltd. 1995.



                            I checked out the university library again today... and I believe that they have all of the books listed above, or at least something like them. I also realized that any sort of book on electronics theory written in the 50's is about 80% tubes and 20% (if that) transistors..... sadly, a lot of the books that I really want to find, weren't there!! I forgot to see if they were checked in... Usually when I check out books on Vacuum tubes the person at the desk is like "Woah!! Nobody has EVER checked out this book before" at least not since the built that library...

                            There is a great lecture given about the birth of the vacuum tube....

                            The birth of the vacuum tube, "the Edison effect."
                            by Humy, Fernand Emile d', 1873-1955.
                            New York, Newcomen Society of England, American Branch, 1949.

                            It is great reading, this guy just praises Thomas Edison for his discovery of the edison effect and those that used it in vacuum tubes... there is also a great part where he talks about the vacuum tube being inspired of God and one of the best things God has given us -- It should be like the Tube-heads Bible - We should all have quotes from it on our walls and our webpages... we should have our wives cross-stitch things from it four the walls in out rehersal halls and studios..

                            maybe I should just make a .pdf and post it on my webpage when I get it done...


                            Hey, I've got a question about power transformers for an upcoming amp project.. I'm going to build a class A/B amp that can use anything from 6V6's to KT88's.... I'll be using terminal strips so that I can mod it easily... I will be basing the power amp section of the marshall 1989. I have recently read that with a choke in the filter circuit it gices you a lower voltage than that you would expect wiht just capacitors and resistors. I'm looking to get about 425-450V on the plates for the EL-34s... What value of power transformer should I use to get this... What would be the properties of a good choke to use in this? (DC resistance, voltage rating, curent rating, inductance value) I was looking into get a 300-0-300, but with this new info, it doesn't look that it will get me the voltage i want (I'm going to use a solid state rectifier)

                            I was also thinking of throwing a choke in my DSL401, just to see what it does... This would lower the voltages to a "safe" operating point (the DSL runs them over 100% plate dissipation), and I could also perhaps install a pentode/triode switch.... But this is really the whole reason I am building the other amp - so I can play with it and see how different components/configurations/tubes give different sounds... It would be more a pain to try to do all that with a pc board based amp - especially when I would have to find someplace to install the choke!! (There isn't a lot of room in there!!)

                            Comment


                            • #44
                              Originally posted by gusfinley


                              Funny you mention air quality... I live in a little valley and there are TONS of cows - so many in fact that "methane emissions" relatating to cows cause 60% of the air pollution!! When we get inversions they don't let the kids go outside at school because the air gets worse than L.A.!! Its kinda wierd.... They tell us to stop driving, but the big problem in the cows!!

                              J.J. 50-50s go for about 8-9 online, so you are saving a few bucks...


                              Right on. I guess the cows and I are doing pretty well


                              Originally posted by gusfinley

                              I also realized that any sort of book on electronics theory written in the 50's is about 80% tubes and 20% (if that) transistors.....
                              I forgot to see if they were checked in...
                              Funny how the best books are gone. Yes the 50 and 40s are both great eras for tube reference.

                              The birth of the vacuum tube, "the Edison effect."
                              by Humy, Fernand Emile d', 1873-1955.
                              New York, Newcomen Society of England, American Branch, 1949.

                              ...It is great reading, this guy just praises Thomas Edison for his discovery of the edison effect and those that used it in vacuum tubes... there is also a great part where he talks about the vacuum tube being inspired of God and one of the best things God has given us -- It should be like the Tube-heads Bible - We should all have quotes from it on our walls and our webpages... we should have our wives cross-stitch things from it four the walls in out rehersal halls and studios...

                              I believe in God and I believe the tube is exactly as described above! But my wife left me for a younger man
                              Hey, I've got a question about power transformers for an upcoming amp project.. I'm going to build a class A/B amp that can use anything from 6V6's to KT88's.... I'll be using terminal strips so that I can mod it easily... I will be basing the power amp section of the marshall 1989. I have recently read that with a choke in the filter circuit it gices you a lower voltage than that you would expect wiht just capacitors and resistors. I'm looking to get about 425-450V on the plates for the EL-34s... What value of power transformer should I use to get this... What would be the properties of a good choke to use in this? (DC resistance, voltage rating, curent rating, inductance value) I was looking into get a 300-0-300, but with this new info, it doesn't look that it will get me the voltage i want (I'm going to use a solid state rectifier)
                              Don't confuse a Choke-input filter with a Cap-input filter that uses a choke. Common mistake. There will only be a large drop in voltage with the former but you would never use it in a guitar amp unless it was low power class A for a number of reasons. For a proper design Cap in Pi filter you could use this formula-
                              Et=Eo+1(R1+R2+Rr /1000) / 1.15
                              Or you can just go to the either the London Power or Hammond web site and look up their recommendations.
                              It is much easier to determine the correct smoothing choke than an input choke. For a smoothing choke values around 10 to 20 henrys are used commonly. The windings must be insulated from the core by at least the full DC output voltage of the supply and also be able of handling the current at maximum load.


                              I was also thinking of throwing a choke in my DSL401...(There isn't a lot of room in there!!)

                              You answered that yourself. I like the DSL. It kind of takes pedals better than my DIY so far. Though I do not use anode bypass caps like every stage I looked at in the DSL and have a bit more gain on tap so am less likely to want a boost in the front. I use FQ toned FB loops as they suck less tone. IMO, just get the DSL working and then build your own amp for research! It

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                              • #45
                                As far as chokes in the amp go - I was using the power supply desinger from dancanamps.com. I had it set up to a CL filter with a choke in place of where the resistor would be on a RC filter....

                                I'll check the suggested websites for more info...

                                Also, Do you where I can pick up a replacement 15mm dual ganged A200K pc mount pot from? Is there some place I can order marshall replacement parts from?

                                thanks so much for all of your help, I've really enjoyed the discussion....

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