AX84 BBS Threads with new messages as of Fri, Oct 24th, 2014 @ 20:41:33 http://ax84.com Amp Parts and KitsDoberman Music Products, LLC offers a variety of parts and kitshttp://shop.dobermanamps.com AX84 1x12 Tools Needed(by ledzepp007) Hi all, I apologize if this has been discussed (I have not found it through the search). I am just getting started with this and I thought I'd start with the woodworking side of things (speaker cab, head cabs) before I dive in to the electronic side. I have a cheapo Seismic 1x12 with a WGS speaker inside (the speaker is fantastic). It sounds ok, but it is an eyesore. I'd love to build the AX84 cab, but I have several limitations: 1) I don't have a lot of cash right now (saving for a wedding, just moved), 2) skill, 3) lack of space (live in an apartment in which there isn't a ton of space), and 4) no real woodworking skill (that I know of). The things I have going for me are that I'm pretty smart and I've been reading about wood joinery, different woodworking tools (saws, routers, etc). My question is this: in order to make the AX84 1x12, what is the bare minimum in terms of woodworking told that I would need, keeping in mind that they would need to be in a small work environment? I really appreciate your help in advance.Fri, 24 Oct 2014 20:29:13 -0400 http://ax84.com/bbs/dm.php?id=486947 Getting Ready to Build(by Tim Mc) I'm stoked. Yesterday I received a message that parts for my P1-eX have shipped. This will be my first tube amplifier. Years back I earned a living as an electronics tech and even though that was all pretty much solid-state gear I'm not concerned about the electronic build itself. How are people finishing and enclosing their amplifiers? I've considered just painting or powder coating the chassis and mounting it on a simple wood base for the world to see but I also like the idea of a nice, professional looking enclosure. Is there a gallery of finished user projects to look at anywhere to get some ideas? If you build in a cabinet, how are you labeling things or making faceplates? Thanks in advance! TimFri, 24 Oct 2014 17:59:09 -0400 http://ax84.com/bbs/dm.php?id=486979 design around ignorance(by Kursad K) OK, this is off topic: <a href="https://answers.yahoo.com/question/index?qid=20080917070550AAOR81j " target="newwin1414197693">[link]</a> It says you cannot use %100 pure antifreeze because it is a poor heat conductor and the maximum amount of antifreeze in an engine coolant should be %70 and the most common compromise is %50-%50. Makes sense. But I have often seen that this advice is completely ignored. If a mechanic has even remembers to change the engine coolant, they just replace the radiator contents with %100 pure antifreeze. Assuming that some of the coolant is in the engine, the result is not immediately %100 pure antifreeze, of course, but it would only need a few replacements to exceed the safety limit of %70. Obviously the switch to the long life antifreeze has a reason: if they'll do it wrong in every time, it's better to reduce the number of wrong replacements. I don't know if this interests anyone here. Just wanted to share the info. KursadFri, 24 Oct 2014 17:21:02 -0400 http://ax84.com/bbs/dm.php?id=486972 Weber-esque 5F4 using '60 Conn Organ Chassis(by Jonathan Haynes) First post here. I come from ham radio kit and homebrew land, and this is my first project. I have several donor electric organs on hand and dove in with a Conn 430 chassis. Looking it over, I saw a 5U4GB rectifier, a pair of 6V6GCs and a trio of 12AX7s, along with a very husky PT, OT and perhaps other salvageable parts. After stripping it down to the bare metal, I decided to use a Weber 5F4 layout and schematic as a guide, and built the amp freehand from there. I've learned a lot so far--especially about observing layout conventions to GREATLY ease troubleshooting and servicing the finished amp. After finding a few goofy mistakes the amp started coughing and sputtering to life--but I have problems. First of all, I cannot get any clean tones whatsoever. My measurements and calculations based on the Uncle Doug video to determine plate dissipation. It appears I have avg 14.8Watts of output, but I may have put the cart before the horse. So I will back up--What considerations should I have in mind when determining the usability of this PT with the Weber design? I don't have the OT voltages on hand, but supposing they are 20% or so too high, what is the typical method of dropping these voltages, and where do I find out what is recommended? I have a current limiter and variac, as well as various DMMs and an oscilloscope, although I don't see one typically used. Please point me toward the right publication, site--or if you don't mind, let's chat on the phone or textually online. I have a feeling my questions will be simple enough for any relatively patient amp-a-holic to answer. This amp's right on the edge of being worthy of building a cabinet--but not quite yet. Thank you, JonathanFri, 24 Oct 2014 11:07:37 -0400 http://ax84.com/bbs/dm.php?id=486903 Epiphone Valve Special plate voltage(by chee16) So I have done a lot of mods to my Epiphone Valve Special, essentially converting the preamp to as close to the Matchless Lightning as possible, eliminating the DSP and now trying to bias the EL84 properly. I used this tutorial for biasing (though it is for the Valve Junior) <a href="http://web.archive.org/web/20071213061717/http://www.diycustomamps.com/valvejunior.htm " target="newwin1414197693">[link]</a> So using the method I have my dissipation at about 14watts, that is with a 270ohm/2w resistor from the cathode to ground, where the stock resistor is 220ohm. My cathode voltage is 11.75V, and my anode voltage is 339V which seems way to high. Using those numbers for the dissipation gives me just over 14watts. Too high. I measured my wall voltage and it was 122V. In the article the guy talks about upping R10 from 220ohm to 1kohm. That sound fine except the Valve special doesn't have an equivalent resistor. Here are the VJ schems <a href="http://www.sewatt.com/files/sewatt/StockVJ_1-3.pdf " target="newwin1414197693">[link]</a> Here is the schem of the Valve Special, I put in the values as they were really blurry <a href="https://lh5.googleusercontent.com/-NqQklh3ewMA/VEGkz-jhFHI/AAAAAAAAC_Q/_--sf54jIok/w388-h221-no/evspowersection.png " target="newwin1414197693">[link]</a> Version 1 of the VJ doesn't have the R10 resistor either, so I am thinking I could safely add one into my circuit. Does anyone have any insight into this? I doubt specifically to this model amp as the VJ craze is pretty much gone, but hopefully someone can tell me if I am thinking correctly. It should bring the B1,2,3,4 voltages down correct? Looking the the VJ schems and comparing Version 1 and Version 2 it seems that when they added R10 (220ohm) it dropped the B1,2 and 3 voltages down. Thank you, I hope I was clear in my description. Fri, 24 Oct 2014 11:00:47 -0400 http://ax84.com/bbs/dm.php?id=486812 advice on building and designing amps for a living(by CChurchill) I fell into this rabbit hole of amp, guitar, and effects building about five or six years ago. To make a long story short, building tube amps quickly became as much of an passion as playing guitar. I've been reading everything I can get my hands on regarding the subject. I want so badly to build and design amps for a living, and the thought of doing anything else blows(quite frankly). It can be frustrating learning on my own, but there aren't many job postings for Tube amp apprentices. I'm looking for any advice I can get. Fri, 24 Oct 2014 07:04:14 -0400 http://ax84.com/bbs/dm.php?id=486788 Adventures in Digital Control(by Chris Hurley) As some of you know, I've been thinking about making an amp or preamp with some amount of digital controls for a while. I certainly enjoy the traditional feel of an amp with regular knobs but I also enjoy tinkering outside the box a little bit. Some things are really easy to bring under the micro-control. Muting part of one channel while unmuting another is easy with LDRs or other switching devices. Cathode bypass caps should be easy to switch in and out. The beauty of the microcontroller is that you can pretty much make it bring high or low any low-current on/off device that can run on 5v in any order that you command. I immediately start to think about all the things I might switch in or out of a circuit- bypass caps, shunts to ground to reduce gain throughout the circuit- maybe even whole tone stacks. The sky is the limit. Yes... I know... Some of you just prefer to turn a knob and "who would ever want a computer in the amp?" I get that. This thread isn't for you- its for people who are interested in doing more than that for whatever crazy reason. I can imagine collecting up various groups of switch settings into channels. "Turn off all the bypass caps, attenuate the gain and activate tone stack A" could be a clean channel. "Turn on all bypass caps and activate stack B" could be a lead channel. With MIDI, all of these things could be controllable as continuous controllers- easily. One of the harder things for me to handle so far has been digitally-controllable interstage attenuation (i.e. pots). Here's what I've either tried or researched: * Controlling the current to a MOSFET for the purpose of draining more or less preamp audio signal to ground or as the bottom part of a voltage divider: It works but it distorts the signal. Presumably because the MOSFET acts as a diode and only conducts one half of the signal. Evidently, you can put a pair of MOSFETS back to back to pass AC signals but it appears the behavior between all the way off and all the way on varies wildly between units. That would mean you'd have to match pairs of them. I assume this does something bad in terms of load to the preceding stage too. * Using photoresistors (LDRs) in a pair as a potentiometer. These also seem to vary wildly so that X milliamps of current on one unit might produce 220k of resistance while the same current on another produces 470k of resistance. More matching. They could be used as switches- the best ON resistance I can get is about 300ohms. * Digital potentiometers: Where to begin? They're generally limited to the IC supply voltage, so you have to attenuate the signal to 5v or whatever it is before the pot. Thats bad enough but then you also can't have a signal that goes below 0v (which our AC-coupled audio does) which means you'd have to reference the signal to a positive DC around 2.5 volts. Of course, you have to amplify it back up again. * Resistor ladder with relays or mosfet SSRs- this will probably work but it gets big and expensive in a hurry- the more steps of attenuation you want, the more resistors and relays you need(*). * turning on bypass caps and connecting hard-wired voltage dividers in groups. This would work but it isn't very granular. Am I missing some obvious way to control gain between stages via a digital device? Perhaps there are other ways I should be considering. (*) I've been working on a board design for such an animal- I made a 10 position "digital" potentiometer with a switchable bright cap. The microcontroller on the board would be sent simple up/down commands to change which relay (wiper) was active. If anyone wants a link to the oshpark shared PCB project, let me know. Fri, 24 Oct 2014 05:15:20 -0400 http://ax84.com/bbs/dm.php?id=486908 Mic preamp phantom power(by DanGu) Hi. I'm designing a tube mic preamp (2 channels), and for the power supply I decided to use an hammond 370AX. So with this transformer I decided to use the 50V bias tap to generate the 48VDC phantom power for the mics. Obviously it as to be regulated, so my choice fall to those LR8 regulators (12-450V regulation range), using 2 of them (one for each channel). My only doubt is: Can this regulator supply enough current to power on the mics? Some say it has 10mA max output, others 20mA of max output. Or should I consider to use something else like a tl783(1.25-125V 700mA out)? The max current draw of each channel (if shorted to ground) would be 14mA with 48VDCFri, 24 Oct 2014 04:47:14 -0400 http://ax84.com/bbs/dm.php?id=486907 loose farty bass(by bullpeters) I got loose loose farty bass in my build. It seems I am not the only one.I have read Lots of threads lots of proposed solutions but no posts that I could see with a solution. I have listened to the clips and didn't hear a tight lower end.but that could be me. It could all be me :) so is it my build, my cab, or inherent to the schematic/system. I love everything about this amp, execpt the bass, which sounds like a fuzz pedal. I just want to know if its fixable or just part of the "flavour" of the amplifier. opened back cab 12 inch celestion, and I have regulated all the power. Ht lt bias etc. The power supply seems to be fine. The layout is as per the document. Fri, 24 Oct 2014 00:40:15 -0400 http://ax84.com/bbs/dm.php?id=486926 AX*$ SEL KT88 for sale(by automap68) AX84 SEL with KT88 and the 2 stage pre amp Built 2 years ago. Finished as a project and just sat. Lots of pictures of my build on this site. Just happen to be cleaning out my closet. If anyone would like it let me know Please email me at bassk94@yahoo.com If you search my name you will find the original build thread from 3 years ago with specs I tried to post a link to it but it won't let me Make an offer. Think i spent $400 in parts alone not to mention 2 months building it. Would let it go cheap <a href="http://i1373.photobucket.com/albums/ag378/automagp68/IMG_1166_zpsd582e2ef.jpg " target="newwin1414197693">[link]</a> <a href="http://i1373.photobucket.com/albums/ag378/automagp68/IMG_1169_zpsc56aa08b.jpg " target="newwin1414197693">[link]</a> Thu, 23 Oct 2014 18:05:44 -0400 http://ax84.com/bbs/dm.php?id=486756 Did They Get It Right?(by Douche Baggins) Blackstar's TVP: True Valve Power. Does it really compare? Youtube Demo: <a href="http://www.youtube.com/watch?v=SAu8AcSvy1I" target="newwin1414197693">[link]</a> Thu, 23 Oct 2014 10:52:43 -0400 http://ax84.com/bbs/dm.php?id=486854 Anybody still using leaded solder?(by Kursad K) <a href="http://en.wikipedia.org/wiki/Lead_poisoning " target="newwin1414197693">[link]</a> "No safe threshold for lead exposure has been discovered—that is, there is no known sufficiently small amount of lead that will not cause harm to the body." (quoted from the above) KursadThu, 23 Oct 2014 00:30:50 -0400 http://ax84.com/bbs/dm.php?id=486826 Question about SEL vs Hi-octane(by Brian CA) Hey guys! I built a Hi-Octane a couple weeks ago and I'm loving it! I had a question though...when I look at the SEL schematic, I notice R13 and D3, that is not on the Hi-Octane schematic. I also have two weird problems on my Hi-Octane: (I have the rythm/lead switch mod installed) #1: When I'm on the clean channel, I can always hear a little bit of distortion in the background, when playing, as if a bit of the signal is leaking through to the other preamp stages and going through the power tube. Would installing R13 and D3 help solve this issue? #2: I can some weird alien type fuzz/noise that changes pitch when I fool around with the two gain knobs. I'm pretty sure it's a grounding issue, so I'll put my mains AC ground to the chassis instead of to the input jack. Can I also run a wire from my ground bus to the chassis for the circuit? Thanks for the help :) BrianWed, 22 Oct 2014 15:13:11 -0400 http://ax84.com/bbs/dm.php?id=486890 1-5 Watt Pentode tubes for SE project(by Alva Goldbook) I keep thinking about building a low watt SE amp, for a high gain British type sound. I'd like to build this guy for *cheap*, so a low watt amp that won't draw too much current would be appealing. I'd like to get something that draws less current than a EL84 or a 6V6, so I don't have to lay down too much money on a power transformer. I've thought about using a 12AU7, but I've heard a lot of folks report that they don't like triode sound very much. So I'm thinking that maybe there's a more rare tube (that I'm currently not aware of) that will get the job done. Any suggestions?Wed, 22 Oct 2014 15:06:25 -0400 http://ax84.com/bbs/dm.php?id=486818 Trouble with ECF80(by JaapK) No matter what I try the ECF80, a small signal pentode and triode in one tube, is giving me trouble: oscillation that is! Amp is a simple 2 gain stages preamp: pentode ecf80 - volume pot 500k - triode ecf80 Rp100k and Rk 6k8 B+ around 90 V Nothing special. Checked everything, grounding, shielded wire etc Is there something with that tube, I start wondering. Anyone ideas or experience with that tube? Like to hear, its driving me $##%%%*** thanx JaapWed, 22 Oct 2014 07:13:44 -0400 http://ax84.com/bbs/dm.php?id=486885 slow guitar build(by tedmich) getting a project going, found the (wing) wood in the road ~10 years ago in PDX just finished it up with Liberon's Finishing oil, 5 coats with only 5h between coats, then 3 coats Renaissance Wax <a href="https://lh6.googleusercontent.com/-JkBIEViwzVs/T7-025avWlI/AAAAAAAAD8s/NIasRpVBrIY/s640/DSCN4792.JPG " target="newwin1414197693">[link]</a> <a href="https://lh3.googleusercontent.com/-Pw3i2un4pcg/T7-05TJO0ZI/AAAAAAAAD8U/3o-9GovZ1Ys/s800/DSCN4793.JPG " target="newwin1414197693">[link]</a> <a href="https://lh4.googleusercontent.com/-ewE2IGYGusY/T7-07vFu8dI/AAAAAAAAD8c/vLFUnu5EwjM/s800/DSCN4794.JPG " target="newwin1414197693">[link]</a> here’s the 30” scale LMII Mad. Ebony fretboard, slotted to 3 octaves with maple filling slots 35/33/31 (and the sausage fingers which make this necessary!) <a href="https://lh3.googleusercontent.com/-Ijw_qCnrTlg/T7qvQ705asI/AAAAAAAAD6I/ddGyK2L699g/s800/DSCN4776.JPG " target="newwin1414197693">[link]</a> heres how it will go together with Kahler 8 string bridge ($165) “blem” and the EMG 808 hole <a href="https://lh3.googleusercontent.com/-oZfFpZ--OU8/T7FbY4uCKAI/AAAAAAAAD2s/DWisiHowOZY/s640/DSCN4756.JPG " target="newwin1414197693">[link]</a> Wed, 22 Oct 2014 05:02:32 -0400 http://ax84.com/bbs/dm.php?id=463785 Phase Inverter Buzzed(by Dire Wolf) I am getting a loud buzzing from my PI even with the preamp tubes out. I have used a wooden pencil to poke and prod and found as I tap on the grid connection wire for one side of the PI I can hear the tapping in the output. The preamp works and can be heard however this buzzing is dominate. With a lightbulb limiter the sound is still present, not as loud. I have built the circuit before and had no issues. The connection in question is pin 7 of the PI. Any thoughts. Here is the schematic. <a href="http://ax84.com/media/ax84_m53.pdf" target="newwin1414197693">[link]</a> Tue, 21 Oct 2014 14:58:10 -0400 http://ax84.com/bbs/dm.php?id=486127 50W PP standalone - OT wiring confusion and other questions(by EeroNiemela) I'd like to build the standalone 50W PP as my next project, and at the moment I'm a bit confused about the OT wiring. It says on the 50W PP schematic to use the 56k NFB resistor when using the rotary impedance selector (which I'd like to do). What confuses me is that the 56k value is for the 8 ohm hookup, but it is always connected to the GRN (4 ohm) wire on the 1650N OT. So why 56k and not 27k for the NFB resistor? Also I can't see how the 16 ohm position (pos 1) on the switch is supposed to work. According to the 1650N datasheet, the secondary windings are as follows: BLK-GRN (0-4 ohm) BLK/YEL-GRN/YEL-YEL (0-4-8 ohms) Now, the 16 ohm position seems to connect GRN to BLK/YEL and GRN/YEL to output jack tip. BLK is ground. So that would put two 4 ohm windings in series for a total of 8 ohms, not 16 ohms. What am I missing here? Also, how is the Hammond 1650N for this amp? I understand that the Hammond OTs are nothing specieal, and I'd like to go for something nicer. I could get an InMadOut (Italian brand) transfomer for the same money: <a href="http://en.uraltone.com/inmadout-output-transformer-tuslo50-soldano-slo50.html " target="newwin1414197693">[link]</a> It has a 4.4k primary instead of the 4.3k of the 1650N, but this would be close enough I imagine. Also as for the choke, I assume it's not a problem to substitute the Hammond 156L for a bigger one, such as the 159Q (7H, 150mA, 100R, 500V? And I assume I could increase C1 to 100uF for a punchier response? Thanks!Tue, 21 Oct 2014 11:00:47 -0400 http://ax84.com/bbs/dm.php?id=486739 Dr. Z, Mini Z Schematic(by Alanh) Anybody have a Dr. Z, Mini Z Schematic? ThanksTue, 21 Oct 2014 09:12:26 -0400 http://ax84.com/bbs/dm.php?id=486796 Look what the cat dragged in(by Chris Hurley) Hey guys- I wanted to pop in and say "hello" since I've been away for a while, though I have enjoyed emailing some of you from time to time. The last few years had been somewhat rough due to family things but I'm mostly through all that now and I'm starting to get the bug to build again. I've been tinkering around with a few odd-end ideas here and there but haven't harvested any real fruit. I'm currently fiddling with ideas for how to control various things in an amp using a microcontroller. Switches and shunts are the easiest things to control but I'm not having much luck replacing a potentiometer with something I can control easily from a microcontroller. I tried to use a MOSFET as part of a variable resistor- it "worked" but distorted as the controlling voltage was dropped. Yuck. I could easily use some sort of switching device (LDRs, relays, etc...) to switch the wiper on a resistive ladder. That will work but it will take up a lot of space and a lot of controller lines. I bought a couple of digital potentiometers which appear to be resistive ladders with mosfet switches for the wiper. The biggest issue with these is that they will only tolerate 5v, so you can't just use them anywhere in the amp. I haven't tried them- they may sound bad too. Motorized pots aren't especially easy to come by. I could use a stepper and some sort of linkage to a regular pot, but thats going to be large and burn a lot of controller pins. Perhaps nothing beats the sound of a well designed single channel amp without any of this nonsense but its fun for me to think about and fiddle with. I hope everyone is doing well. -Chris Tue, 21 Oct 2014 07:48:34 -0400 http://ax84.com/bbs/dm.php?id=486403 WGS ET-65 vs WGS Vet-30(by JeffW) I made a clip with the first half being the ET-65 and the second half being the Vet-30. Both in my slant front with a e609 mic. Thought it was kind of interesting. <a href="http://www.mediafire.com/listen/ji58zsmqbxa5t68/MiniJCM.mp3" target="newwin1414197693">[link]</a> Tue, 21 Oct 2014 07:07:40 -0400 http://ax84.com/bbs/dm.php?id=486785 First build, looking for a different form factor(by DucJustin) Good evening all, I'm starting my first build, and I'm looking for a little input on why the form factor for the P1-eX is as it is. As I understand it, it's somewhat important to keep the power transformer away from the signal path if possible, but I'm still curious why this amp is laid out on such a large board. Is it simply because of the traditional size of the amp chassis already out there? I'd really like to build my chassis a lot more square. Probably double stacking the controls on the face, and hoping to fit the whole thing into a cabinet with similar dimensions as a Epi Valve Jr. Is there some reason I couldn't squish up the layout? When I'm mocking my components up, there seems to be plenty of room to do that. -JustinTue, 21 Oct 2014 06:57:30 -0400 http://ax84.com/bbs/dm.php?id=486856 Getting less negative feedback(by David Hodgkins) Looking at my Ecolette. Schematic here: <a href="https://www.flickr.com/photos/39482018@N05/8343916624/ " target="newwin1414197693">[link]</a> This amp is super clean and bright. Even jumpered and dimed there is virtually NO breakup. I'm mostly fine with the cleaness, but this amp is super bright as well as lacking in overall volume. (Not that I truly NEED more) But I just feel that there should be more. In order to get a warm sound the presence needs to be all the way down and the treble on about 2. I just think that there's altogether too much NF. If this was a standard NF loop, I would just increase the resistor, but I can't really understand this topology. This is an early PC board amp, so I'm somewhat limited on my mods. If I lift C21 and R38 I get a lot more volume, but I loose my presence control (which I never use), but I'm just looking for a more educated and sensible mod. Any help is appreciated! Tue, 21 Oct 2014 02:18:16 -0400 http://ax84.com/bbs/dm.php?id=486730 Anyone willing to build my PP reverb and give suggestions?(by Darren Porter) I was wondering if anyone would like to build my PP 12AT7 reverb and give their experienced insight into improvements in the circuit and share your layout ideas. This is my first attempt at a design and scratch-build. I think it sounds pretty good but I also think it could be better but I really have no clue how to improve it. It is a very simple design, two tubes. If you have a Firefly it would be extremely easy to convert it over.Mon, 20 Oct 2014 14:42:35 -0400 http://ax84.com/bbs/dm.php?id=484881 Looking for a project reusing these transformers(by Stack) I have an old ADA Microtube 100 that hasn't worked in years, I pulled the transformers and thought that they could be used in a standalone preamp project. I've looked at Bancika's blackbox, but I don't think this iron will support that. I already have an HO and a firefly which would seemingly be good projects but I've already been there. Here is the link to my drawing of the original supplys from the ADA <a href="http://s1377.photobucket.com/user/StacklerAmplification/media/ADA-PSU_zpsf6250676.png.html " target="newwin1414197693">[link]</a> the voltages got cut off my scan, they are: 170V B+ -12V Filament following the LM7912 I found an ADA xfmr from an MP-1 to get you a relative size of the transformer <a href="http://www.ebay.com/itm/ADA-MP-1-Power-Transformer-/331345563239?hash=item4d25bc0e67 " target="newwin1414197693">[link]</a> There is also a torriodal transformer of unknown rating, 22.5V - 0 - 22.5V - 0 which I haven't figured out what to do with either... All ideas welcome.. Thanks in advance. -TroySat, 18 Oct 2014 18:31:09 -0400 http://ax84.com/bbs/dm.php?id=486754