AX84 BBS Recent Posts as of Tue, Jul 29th, 2014 @ 01:09:40 http://ax84.com Amp Parts and KitsDoberman Music Products, LLC offers a variety of parts and kitshttp://shop.dobermanamps.com RE: Class A and AB amplifers(by Balijukka) Yesssss!!!!! Class A fight again. Been waiting for it :DTue, 29 Jul 2014 01:02:12 -0400 http://ax84.com/bbs/dm.php?id=485732 RE: About the logical workflow...(by gdivella) <div class="quoteblock" >On 07/28/2014 @ 09:07, PaulP wrote : <div class="quoteblock" >On 07/28/2014 @ 02:40, gdivella wrote : : Hello everybody! I'm totally newbie at building my own amplifiers. At first I'd like to know what is the logical workflow a designer follows in his mind to put all the parts together... for example: how do I set the bias values for a bjt? : : : : Thank you very much : -- : : </div> : : You gotta start with the forest, then work down to the twigs! : : If you have the parts already, or key parts like the transformers, then you design around them. If you're starting from absolute scratch though, with an excess of money: : : 1. How loud do I want this to be? : 2. How many speakers do I need to accomplish that loudness? : 3. How much power do I have to deliver to those speakers, and at what impedance(s)? : 4. What tubes and how many to generate that power? : 5. What power transformer & output transformer to match those tubes with that power? : 6. How do I want the power supply to perform? Stiff, sagging, noise-free? : 7. What phase inverter do I want to use? : 8. How do I want the preamp to sound? Hi gain, low gain, channel switching, what tone controls, etc etc etc. : : : Or, more commonly: : : 1. Ooh, neat! I'm going to copy *that* amp and change this one little thing. : 2. Wow, a custom Hyper Blasting (my last name) Amp with shimmering glassy cleans and warm creamy low-fat overdrive with Class #1A tube warmth and... and... where'd I leave that guitarist thesaurus?! -- </div> Hi Paul, thank you for your answer! It would be great if I could get your contact (email address or even Skype) to have some discussion with you: i definitely need a mentor to start working with these things. Please feel free to write me here: gdivella*AT*gmail*DOT*com Mon, 28 Jul 2014 23:52:21 -0400 http://ax84.com/bbs/dm.php?id=485731 RE: 5F2A(by barefootboy) Thanks, I'll go back and check again. Some times a day away jelps refresh the eyes. Bill Mon, 28 Jul 2014 13:06:54 -0400 http://ax84.com/bbs/dm.php?id=485730 New Amp - pics(by Stevo) Hey all, just wanted to share pics of the new beast. This is my most ambitious build so far - complete with two tone cabinet covering and hand printed faceplates and tag strip construction inside! The preamp is an Uber lead - stock so far - while the power amp is a 50 watt push-pull with 6CA7s fed by a cathodyne PI (lifted from Merlin's article here: <a href="http://valvewizard.co.uk/cathodyne.html " target="newwin1406610585">[link]</a> ). The album is here: <a href="http://s149.photobucket.com/user/stevpo/library/Omega?sort=2&page=1 " target="newwin1406610585">[link]</a> When I get around to recording some clips, I'll revisit the thread to post them. In the meantime, however, I'd just like to say this is amp is already my favorite. The preamp gets nice and heavy, but remains tight and focussed. Backing off on the gain really cleans the amp up, though, which is pretty cool. If I were to build this amp again, I'd probably add an Orange style FAC to introduce some more bass at lower gain settings, but I'm not really using this amp for low gain stuff anyway. The power supply is rather more conventional than the UberSEL - no choke, no capacitance multiplier, 100uF reservoir cap with 47uF caps for the rest. Kudos go out to Alex for the preamp design and Merlin for making his knowledge and schematics freely available.Mon, 28 Jul 2014 11:23:46 -0400 http://ax84.com/bbs/dm.php?id=485729 RE: Heyboer Xformer(by Lou Glorfeld) Got it. Thanks!Mon, 28 Jul 2014 09:56:23 -0400 http://ax84.com/bbs/dm.php?id=485728 RE: 5F2A(by PaulP) <div class="quoteblock" >On 07/27/2014 @ 12:29, barefootboy wrote : It's been a few years since my last build and I'm missing something on this build. I used a Weber 5F2A schematic for the build. The power transformer is a P-TF22772 and the output transformer is a P-TF22905. My A, B, C, and D voltages are high. : A=460 : B=460 : C=404 : D=280 : : the 5Y3 2=460,4=350,6=349,8=460 : : the 6v6 2=9.5,3=460,4=404,5=-5,7=15.6,8-54.2 : : the 12AU7 1=35.3,2=-.5,3=4.7,4=9.3,6=37,7=15.7,8=5 : : the heater voltage are real high and the others seem to be high too. I'm starting to think the power transformer is over producing. The line voltage is 120. I also have no sound coming out. Any help or suggestions will be appreciated. Thanks, Bil; -- </div> Measure heater voltage as AC volts from one terminal to the other, e.g. between pins 2 and 7 on the 6V6. It looks like that tube's okay, but it looks like you have your heater leg connected to pin 7 of the preamp tube instead of pin 9. Hopefully that's what's causing your crazy voltages. There could be other wiring issues on the preamp socket or power tube socket though. Mon, 28 Jul 2014 09:25:04 -0400 http://ax84.com/bbs/dm.php?id=485727 RE: About the logical workflow...(by PaulP) <div class="quoteblock" >On 07/28/2014 @ 02:40, gdivella wrote : Hello everybody! I'm totally newbie at building my own amplifiers. At first I'd like to know what is the logical workflow a designer follows in his mind to put all the parts together... for example: how do I set the bias values for a bjt? : : Thank you very much -- </div> You gotta start with the forest, then work down to the twigs! If you have the parts already, or key parts like the transformers, then you design around them. If you're starting from absolute scratch though, with an excess of money: 1. How loud do I want this to be? 2. How many speakers do I need to accomplish that loudness? 3. How much power do I have to deliver to those speakers, and at what impedance(s)? 4. What tubes and how many to generate that power? 5. What power transformer & output transformer to match those tubes with that power? 6. How do I want the power supply to perform? Stiff, sagging, noise-free? 7. What phase inverter do I want to use? 8. How do I want the preamp to sound? Hi gain, low gain, channel switching, what tone controls, etc etc etc. Or, more commonly: 1. Ooh, neat! I'm going to copy *that* amp and change this one little thing. 2. Wow, a custom Hyper Blasting (my last name) Amp with shimmering glassy cleans and warm creamy low-fat overdrive with Class #1A tube warmth and... and... where'd I leave that guitarist thesaurus?!Mon, 28 Jul 2014 09:07:56 -0400 http://ax84.com/bbs/dm.php?id=485726 RE: Knowledge is Power - pun intended 'cause I think I'm funny(by PaulP) <div class="quoteblock" >On 07/27/2014 @ 04:21, Dave C wrote : : If the AC follows the electron flux which would be opposite to the way it's shown in the illustration (as you suggest) then the signal ends up flowing to ground .. right? The bypass cap will block DC but allow AC frequency manipulation to occur ... that I get. However, once we are below the bias resistor and bypass cap I run into conceptual problems since ground is 0 volts and in my struggling mind this means zero signal. : : How do we get a signal of zero volts back to where it needs to be if it now flows up through the filter cap and on to the OT. Perhaps I'm looking at this the wrong way. Maybe thinking of it as flowing is the wrong idea. Could it be that the signal is just there and the intensity varies depending on at which level or potential you measure it at (cathode versus the anode for example). </div> Think of tubes as "valves" which is really a much better name for them. Like a simple kitchen faucet is a valve for water. Let the faucet trickle water (idle current). Water is flowing (pumped, even) from your well, through the faucet, and out to the septic tank. If you jiggle that faucet, you can make more water flow or less water flow. You can cut off the flow entirely if you want. Or if you turn the faucet all the way open you could be asking the faucet for more water than your well's pump can supply. At no point is your hand scooping water out of the well or pushing it down the drain. You're only turning a knob. The signal from your guitar is a voltage, and all through the preamp it gets passed along as a voltage - how far the knob should be turned. How far the final valves should be opened. Maybe another aspect that would help is differentiating how voltages and currents are measured. You have to measure a current by putting a meter in series with the current flow. Voltages on the other hand are measured with a meter in parallel. Voltage is a potential energy difference. There's a voltage between you and me right now. There's a voltage between your amp's ground and Saturn. There's a "voltage" between someone sitting in a tree and someone standing on the ground beneath the tree, and it doesn't matter if they're 500 feet above sea level if we call the base of the tree "zero volts." So don't look for signal (aka voltage) to "flow" from one stage to the next, because it doesn't. The problem with analogies of course is the physical world follows its own rules instead of the rules suggested by a nice analogy. Hopefully this helps more than it hurts though. Mon, 28 Jul 2014 08:56:18 -0400 http://ax84.com/bbs/dm.php?id=485725 RE: Power tube heater filaments--wiring(by Stevo) <div class="quoteblock" >On 07/27/2014 @ 20:01, Stevo wrote : If you wire them in series, they each get the 6v. If you wire them in parallel, then the voltage gets split - 3v across each filament, which is too low to properly heat the tube. -- </div> Sorry. This should read: If you wire them in parallel, they each get the 6v. If you wire them in series, then the voltage gets split - 3v across each filament, which is too low to properly heat the tube.Mon, 28 Jul 2014 07:08:41 -0400 http://ax84.com/bbs/dm.php?id=485724 RE: Knowledge is Power - pun intended 'cause I think I'm funny(by Stevo) I have personally found this site to be a wonderful tutorial for the next step in understanding electronic circuits: <a href="http://www.funwithtransistors.net " target="newwin1406610585">[link]</a> The sister site, funwithtubes has plenty of great articles and projects, but the funwithtransistors page has a link to the author's Electronics for Non-Engineers text book. The great thing about the internet is now you have all these plans and you can build anything you want, more or less, without having to understand and engineer it yourself. When the time comes that you want to understand, that information is out there too!Mon, 28 Jul 2014 06:32:42 -0400 http://ax84.com/bbs/dm.php?id=485723 RE: Knowledge is Power - pun intended 'cause I think I'm funny(by Pete Allen) Hey Dave, I *think* I see what your question is, but concepts are really hard without wavey hands and lots of words and pictures (much easier when talking to someone). So I'm not 100% sure I understand your question, and I'm aware any answer I give will have huge holes in it because I can't write pages and pages (and that would just be confusing). But we'll give it a go.. <div class="quoteblock" >On 07/27/2014 @ 04:21, Dave C wrote : Conceptually I imagine an AC signal that is amplified and piggybacking on a flat DC signal. We normally couple with AC but it can also be DC ..no problem there. </div> Agree so far <div class="quoteblock" > : If the AC follows the electron flux which would be opposite to the way it's shown in the illustration (as you suggest) then the signal ends up flowing to ground .. right? The bypass cap will block DC but allow AC frequency manipulation to occur ... that I get. </div> Mostly fine. I think you might be getting into a bit of a dead end looking for AC to "flow through". In this case the current through the power valve/transformer has a set point (in this case 55mA), and will go up towards 100mAish and down towards 0mA, and that variation is your signal. <div class="quoteblock" > However, once we are below the bias resistor and bypass cap I run into conceptual problems since ground is 0 volts and in my struggling mind this means zero signal. </div> So if I've understood you correctly, you're wondering why the current path goes back to ground, and how any signal is transferred? If you've got a changing current going through a transformer (i.e. the AC signal), then it induces a current in the secondary of the transformer which is our output. The power tube just has to make a changing current by varying the current flow through the output transformer primary to ground. <div class="quoteblock" > : How do we get a signal of zero volts back to where it needs to be if it now flows up through the filter cap and on to the OT. Perhaps I'm looking at this the wrong way. Maybe thinking of it as flowing is the wrong idea. Could it be that the signal is just there and the intensity varies depending on at which level or potential you measure it at (cathode versus the anode for example). </div> This is the bit I don't understand, but it does sound like you're looking at things the wrong way. The 2nd bit sounds closer than the first. <div class="quoteblock" > : It would be great if someone would draw an illustration of an AC signal generated in a pickup and show how it passes through the system to the OT showing what the AC component looks like at every point in the circuit. Perhaps there is something like this out there? </div> I think for that you might do best to download a simulator and build your circuits; you can then look at voltages and currents at any point in the circuit, and change it to see what happens. I've used LTSpice (which is free) for tube stuff. I can't remember what I had to download to get tubey stuff working, but once it is really helpful. If you don't want the hassle of downloading extra libraries for it, you could build an amp out of depletion mode FETs, and they're not a million miles from tubes. PeteMon, 28 Jul 2014 03:57:13 -0400 http://ax84.com/bbs/dm.php?id=485722 About the logical workflow...(by gdivella) Hello everybody! I'm totally newbie at building my own amplifiers. At first I'd like to know what is the logical workflow a designer follows in his mind to put all the parts together... for example: how do I set the bias values for a bjt? Thank you very muchMon, 28 Jul 2014 23:52:21 -0400 http://ax84.com/bbs/dm.php?id=485721 RE: Power tube heater filaments--wiring(by Stevo) They should be wired in parallel. If you wire them in series, you end up with lower voltage than required for the filaments. For example, suppose you have two identical tubes that take 6v for the filament. If you wire them in series, they each get the 6v. If you wire them in parallel, then the voltage gets split - 3v across each filament, which is too low to properly heat the tube.Sun, 27 Jul 2014 20:01:21 -0400 http://ax84.com/bbs/dm.php?id=485720 RE: Heyboer Xformer(by RickTown) Look at the 20W SE building block. It's shown using the Heyboer. Sun, 27 Jul 2014 19:43:22 -0400 http://ax84.com/bbs/dm.php?id=485719 Power tube heater filaments--wiring(by Caprotesta) Hi all, Regarding power tubes: should heater filaments be wired in series or parallel? Could wiring them in series somehow affect bias current? Mon, 28 Jul 2014 07:08:41 -0400 http://ax84.com/bbs/dm.php?id=485718 Heyboer Xformer(by Lou Glorfeld) I am completing a second HO build with options I started about four years ago. I have everything I need including all components and hardware but then noted that I had bought a Heyboer OT transformer. The wiring values on this transformer are no longer available since the Doberman site no longer exists. Can someone give me the values of the input and output wires on this transformer? I think the correct input wires are green and black but I am not sure of this or any of the other values.Mon, 28 Jul 2014 09:56:23 -0400 http://ax84.com/bbs/dm.php?id=485717 RE: Stoking the boiler for a new build(by ve3vxo) If you liked that link you'll probably like this one more. I found a jewel thread on the Trainwreck and what is going on through the different stages especially in the back end with the interaction between the PI and final pair influenced by NFB and PS sag. Lots of scope traces, DC voltage readings and discussion about the dynamics. Fascinating. A lot of reading but it sure enlightened me about this design! <a href="http://ampgarage.com/forum/viewtopic.php?t=15694&postdays=0&postorder=asc&start=0" target="newwin1406610585">[link]</a> Sun, 27 Jul 2014 16:05:39 -0400 http://ax84.com/bbs/dm.php?id=485716 5F2A(by barefootboy) It's been a few years since my last build and I'm missing something on this build. I used a Weber 5F2A schematic for the build. The power transformer is a P-TF22772 and the output transformer is a P-TF22905. My A, B, C, and D voltages are high. A=460 B=460 C=404 D=280 the 5Y3 2=460,4=350,6=349,8=460 the 6v6 2=9.5,3=460,4=404,5=-5,7=15.6,8-54.2 the 12AU7 1=35.3,2=-.5,3=4.7,4=9.3,6=37,7=15.7,8=5 the heater voltage are real high and the others seem to be high too. I'm starting to think the power transformer is over producing. The line voltage is 120. I also have no sound coming out. Any help or suggestions will be appreciated. Thanks, Bil; Mon, 28 Jul 2014 13:06:54 -0400 http://ax84.com/bbs/dm.php?id=485715 RE: SEL Effects Loop Noise(by JeffW) Do you have a complete schematic you could post? Did you add extra B+ filtering for the new tube? Have you tried moving wires around with a chop stick? I noticed you used a terminal strip ground point directly to the chassis. This is a bad idea in terms of ground noise but may or may not play into your problem.Sun, 27 Jul 2014 11:19:32 -0400 http://ax84.com/bbs/dm.php?id=485714 RE: Stoking the boiler for a new build(by Mitch Markin) Thanks for the link to the Rod Elliott article. As usual, he has some really interesting things to say about the hows and whys of circuit design and common mistakes even the major manufacturers make. A lot of guitar amp designs were done 60 or more years ago and have changed little since. Some of the designers were not skilled engineers, either. But they managed to make amps that have those special tones that we have all come to know and love. Sure the designs have flaws that haven't been corrected. In some cases correcting them would ruin the tone so the manufacturers just keep making them the same way year after year. Then other manufactures borrow heavily from these designs and people clone them for themselves and the flaws continue. Things like a standby switch or HT fuse in the wrong place should be fixed. That's pretty easy. Bias power supplies should use a failsafe pot arrangement. They should have their own winding on the PT or their own separate PT. On a commercial design that might add too much cost. But when building an amp for yourself you can spend as much time and money as you want to make it reliable. As for anode clamping diodes on the power tubes, it looks like a good idea. Even Ken Fischer used them on some of his amps. I don't know how they would affect the tone, though. Try it with and without and see for yourself. It's easy to over think some of this stuff. As Rod Elliott pointed out, there is much trial and error in guitar amp design and what seem to be flaws are actually part of the amp's unique character. A lot of the issues hi-fi engineers sweat over simply don't apply to guitar amps. Just build the amp, try it for a while, then start making changes if you think there is room for improvement. That's part of the fun of building your own guitar amp! Sun, 27 Jul 2014 09:18:53 -0400 http://ax84.com/bbs/dm.php?id=485713 RE: SEL Effects Loop Noise(by DethRaid) Amp circuit: <a href="http://www.majhost.com/gallery/DagonEcelstraun/AmpInternals/cam00150.jpg " target="newwin1406610585">[link]</a> Circuit with the effects send/receive jacks moved for a better view: <a href="http://www.majhost.com/gallery/DagonEcelstraun/AmpInternals/cam00151.jpg " target="newwin1406610585">[link]</a> Electronics before effects send jack: <a href="http://www.majhost.com/gallery/DagonEcelstraun/AmpInternals/cam00152.jpg " target="newwin1406610585">[link]</a> Electronics after effects receive jack: <a href="http://www.majhost.com/gallery/DagonEcelstraun/AmpInternals/cam00154.jpg " target="newwin1406610585">[link]</a> Electronics attached to the tube socket: <a href="http://www.majhost.com/gallery/DagonEcelstraun/AmpInternals/cam00153.jpg " target="newwin1406610585">[link]</a> You can see how the wires to/from the volume pot cross over the power tube socket. I used shielded wire (the gray wire) to try and minimize interference, though. I disconnected the negative feedback loop, but that made no noticeable difference.Sun, 27 Jul 2014 07:51:14 -0400 http://ax84.com/bbs/dm.php?id=485712 RE: Stoking the boiler for a new build(by ve3vxo) Thanks for the tip Mitch. I plan on using the Hammond PT so the humdinger will be something I'll plan on. A couple more questions have come up. 1. On the merit/demerits of a standby switch and HT fuse. 2. On the use of plate protection diode networks. (sorry for the length of this) It seems that the front end of the amp has enough gain to be able to significantly overdrive the finals even in a higher power final tube arrangement which results in forward grid conduction and hence charging the coupling caps between the PI plates and the final grids. This changes the bias on the finals resulting in class B-heading toward class C operation with the result that during the crossover there is a period where the output pair are both in cutoff for a while. The back EMF on the OT can result in severe spikes that can cause a few problems. Here is a link to a better description about half way down (#9-clipping and bias shift). <a href="http://sound.westhost.com/valves/analysis.html " target="newwin1406610585">[link]</a> Since the 4-4-0 uses the standard front end but low power output tubes it seems even more likely that they would be severely overdriven. This probably explains the change from a 12AX7 to 12AY7 in the PI for this low power design. There have been several posts about buzzy/fizzy swirly/phasey sounds at full tilt when the signal transitions between the linear and clipped ranges and it makes sense to me that it would be related to the bias shifting from AB to B and deeper B operation due to the coupling caps charging. What the NFB would do to the whole closed system during these transitions isn't so clear to me but regardless, it seems that various approaches with clamping diodes have been tried at least on the higher power versions. Ken fisher himself used them in some of the original Trainwrecks (Kelly is an example) <a href="http://ampgarage.com/forum/viewtopic.php?t=1408 " target="newwin1406610585">[link]</a> I've read that many people have tried a string of diodes on the plates of the output tubes in many amps, but didn't like the sound. I'm guessing that the junction capacitance of the rectifiers under high reverse bias is quite significant at the 22kohm impedance level so although I like the idea of protection from EMF spikes I won't be surprised to find the sparkle is gone with them in place. Ditto for the zoebel and conjunctive filter techniques right? Diode failures are another thing to consider. Has anyone here got experience with this? Of course eliminating the bias shift by clamping the cathodes and grids would remove the need to put protection networks at the output but perhaps the crossover distortion is part of the character and clean to mean dynamic nature of these amps which is what I am drawn to in the first place? So then what to do? Am I overthinking this? I need to just build something probably. But that will be a winter project. JoeSun, 27 Jul 2014 05:43:52 -0400 http://ax84.com/bbs/dm.php?id=485711 RE: Knowledge is Power - pun intended 'cause I think I'm funny(by Dave C) Yeah I think I read that in one of Merlin's books. Still it doesn't really explain how the signal passes through these components. Conceptually I imagine an AC signal that is amplified and piggybacking on a flat DC signal. We normally couple with AC but it can also be DC ..no problem there. If the AC follows the electron flux which would be opposite to the way it's shown in the illustration (as you suggest) then the signal ends up flowing to ground .. right? The bypass cap will block DC but allow AC frequency manipulation to occur ... that I get. However, once we are below the bias resistor and bypass cap I run into conceptual problems since ground is 0 volts and in my struggling mind this means zero signal. How do we get a signal of zero volts back to where it needs to be if it now flows up through the filter cap and on to the OT. Perhaps I'm looking at this the wrong way. Maybe thinking of it as flowing is the wrong idea. Could it be that the signal is just there and the intensity varies depending on at which level or potential you measure it at (cathode versus the anode for example). It would be great if someone would draw an illustration of an AC signal generated in a pickup and show how it passes through the system to the OT showing what the AC component looks like at every point in the circuit. Perhaps there is something like this out there? Sun, 27 Jul 2014 04:21:52 -0400 http://ax84.com/bbs/dm.php?id=485710 RE: Where to get parts?(by LincolnR) Yup, placed my order from them yesterday. Now I just need to order the more generic stuff from Digi-Key. I'm thinking I might pick up some wood from the hardware store to get started on the cabinet.Sat, 26 Jul 2014 20:12:35 -0400 http://ax84.com/bbs/dm.php?id=485709 RE: Where to get parts?(by Darren Porter) 10% of sale ends Thursday! <a href="http://www.tubesandmore.com/ " target="newwin1406610585">[link]</a> Free shipping on orders $89 or more.Sat, 26 Jul 2014 18:08:00 -0400 http://ax84.com/bbs/dm.php?id=485708