AX84 BBS Threads with new messages as of Sat, Aug 29th, 2015 @ 14:08:15 Amp Parts and KitsDoberman Music Products, LLC offers a variety of parts and kits cool little 2 watt 6v6 SE amp. Smps powered(by Zambo) subject says most of it. Runs on a smps. could probably add another preamp tube, but i wont. One knob - volume. <a href="" target="newwin1440871695">[link]</a> Sat, 29 Aug 2015 11:29:31 -0400 LND150 implementation(by boblove) I'm looking to use a transistor based gain stage for a clean boost prior to a tube based gain stage and while I've been on this forum for several years and have successfully built several amps, I'm still kind of a noob. I looking to add an LND150 gain stage and I'm always baffled by the data sheets. I've seen several examples here and else where but I was wondering if any here has an example of (resistor values) and biasing..... I know this is probably alot easier than im making it out to be.Sat, 29 Aug 2015 10:44:30 -0400 Firefly PCB Layout(by DarkV) Hello all! I just signed up here but I've been browsing for a little while now. This is going to be my 2nd tube amp build as my first 5E3 deluxe was far too loud for my apartment. Go figure, I thought "oh 20 watts will be just enough for the apartment" since I've only had SS amps before. I've been gathering all the parts and designing the PCB for my Firefly build and I just wanted to run it by you guys to make sure it's not a total screw up before I etch it. The tube sockets will need to be adjusted a bit since I just received the sockets for measurement today. The schematic is from here, as well as John Calhoun's PCB designs were used as reference material. Also, there were some modifications to some of the earlier PCBs he made and I made sure mine was similar. I originally had R12 grounded to the preamp chain (at R11) but found the Rev 7 PCB mod changed it to the power section. It may look a bit odd because I have the tube sockets coming off the bottom of the board. My mounting will be a bit different as the "bottom" layer of the PCB will actually be facing up with the tubes and all the components facing down. All of the controls and input/outputs are going to be mounted to the panels and wires run to the board. The power supply and 12AU7 all grounds at the top of the board, to a lug on the PT. The inputs and preamps are all going to be grounded to the input jack on the chassis. I figured it worked on my deluxe so hopefully it works here. Here is the link to my ExpressPCB layout. Green is bottom, Red is top, and yellow is silkscreen: <a href=" " target="newwin1440871695">[link]</a> Ignore the "Dark-V Industries", that was just the fun little name I've used for all my projects since high school. Thanks! Sat, 29 Aug 2015 10:04:39 -0400 KT88 screen question(by Denny Gracey) In pursuit of hum and noise reduction for the UHG build (using the stock SEL power supply), I built the rectifier/reservoir circuit on it's only little board, mounted in far corner of chassis, but left the original reservoir cap in place to add an extra filter. My question is which HT should I now feed the OT/KT88 plate for 'ideal' plate/screen condition? B+1 is 370V, B+2 is 350V (currently feeding OT/plate) and B+3 (to screen grid stopper) is 330V. Any advice or links to threads on the topic appreciated. Sat, 29 Aug 2015 06:04:28 -0400 Software amps(by Jamie Anderson) I haven't been building and playing for a while, but built many diy amps here over the years. Just recently I decided to carve out the time to play a little guitar again and have been playing through an app on the ipad, so my ear is completely unfamiliar with real tube sound after such a long layoff. Just an opinion from guys here who build real amps and use software amps as well, does the Bias app sound realistic? My ears have reverted to "tin" and I like playing through the emulation and purposely haven't pulled out my P1, Hi Octane, champs, or any of my other DIY stuff just in the name of simplicity and I want to play and fear that if I get out a real amp again I will be reaching for the soldering iron. Also, I like how I can go in on Bias and "build" an amp in the app, choose tubes, preamp stages, transformers, rectifiers, speakers, etc. Most of my creations in there are mediocre, but some of the stuff others have created sound pretty close to some of the original amps. There is a champ simulation that nails the clean of what I remember my silverface champ sounding like, and the tweed stuff sounds bassy/farty, but in a good way and modelling usually fails pretty bad here. I haven't played around with any high end modelling software/hardware, just various modelling pedals and some windows software. Not trolling, just wondering if my ears have gone completely. Maybe I should pull out the 18 watt or 5E3 builds and forget about emulation. Fri, 28 Aug 2015 11:11:53 -0400 SEL PT options help.(by billpol66) Hi folks , Was wondering if this CT PT will work for an SEL , I'm just not sure about the 6.3@ 2A part. If not is tbere a list of usable sets other then the Hammonds . I am not looking for output power but would like the any octal option eventually. Thanks !Fri, 28 Aug 2015 07:18:05 -0400 Anybody with 6-8 inch guitar speaker cabs (sealed ported)(by sburck) Hello, So I have a dilemma - my ax84 1x12 is way too loud for a bedroom/apartment amp regardless of wattage. It simply moves too much air. Lower power amps (like my ax84 HO) won't push nearly the level of bass through my 1x12 (or 4x12), but the mids and highs are still more than loud enough to piss off everybody. I love how my ax84 1x12 is tuned to sound bigger and tighter than an open back configuration would. Would it be possible to do the same with a much smaller speaker, so as to create a cab that can sound... really good compared to tinny open back small speaker combos? I personally don't know anything about designing speaker enclosures, however I do have a background in math/engineering/computer science, so I can probably understand technical details/theory and make use of software tools if needed. I really have no idea how complicated designing one of these would be, and if it would be quiet enough and possess the desired frequency response (similar to a 4x12 or sealed 2x12)... Here are a couple speakers I have been looking at. <a href=" " target="newwin1440871695">[link]</a> <a href="" target="newwin1440871695">[link]</a> Fri, 28 Aug 2015 06:46:28 -0400 Weird kind of self-split in Magnatone amp(by Doug H) Okay, here's one I haven't seen before: <a href=" " target="newwin1440871695">[link]</a> Check out the cap from the upper screen to lower grid. Also, the upper screen has a 4.7k resistor to lower its supply voltage. WTF?!? Seems like the gain of ea tube would be way out of balance with ea other. I've heard of screen self-split but I thought that was screen-to-screen. Never seen screen-to-grid before... Or is there something here I'm just not seeing??? Thu, 27 Aug 2015 12:48:43 -0400 Tone and OT (by VanHanlon) Hi folks, I built a Firefly a while back, but I'm unhappy with the overall tone. It could really use a bit more top end. How would one go about adding some more sparkle to the sound? Also, when I put it back together recently (had it partially disassembled for mods that never happened), I mistakenly reversed the brown and red primary wires coming from the OT (color blind). The result was an amp that had a real heavy sag after I hit a chord, but the distortion was brutal - in a good way. What did I do? Can it be safely replicated? Thanks, JonathanThu, 27 Aug 2015 07:19:23 -0400 High Gain 12AU7(by Octal57) Hello,could someone look at my rather crude schematic and give me some hints on achieving Mesa/Soldano style aggression but still able to dial back for bluesy stuff? Just to say i always use a simple clean booster in front of my amps so that has to be taken in to consideration and the poweramp will be a fixed bias SE. <a href=" " target="newwin1440871695">[link]</a> ThanksThu, 27 Aug 2015 06:15:45 -0400 Modding AmpMaker donor to HO / L2L - advice needed(by tristanc) I'm in need of some advice for modding my amp to HO or L2L spec. Given the lack of AX84 kits readily available, the information here may be useful for others. The starting point is an AmpMaker N5X, very similar to a P1-eX, but 5W with VVR and being able to use both EL84s and octal valves. This is a great amp as stock, perfect for living room playing. But I found myself needing to use an EQ pedal and boost in front to get the level of OD/distortion I wanted. Ideally, I'd have this in the amp and be able to dial in cleaner sounds with the guitar controls - my dream is to have just amp, cable and guitar. I play blues, classic rock, 90s rock, indie etc. Nothing too extreme - anything else I can use pedals. Of the AX84 designs, both the HO and L2L seem to fit the bill. So the challenge is to modify the N5X to have the additional gain stages of these designs. I've had a go at grafting the circuit designs of the HO and L2L on to the N5X. The two files show the new or modified areas shaded in pink. L2L: <a href=" " target="newwin1440871695">[link]</a> this involved inserting the 3rd stage between the existing 2nd stage and tone stack, then the 4th stage after the tone stack. HO: <a href=" " target="newwin1440871695">[link]</a> the 3rd stage and CF are inserted between the 2nd stage and tone stack. NOTE - I've copied the wiring ciruit for the 1st gain control from the L2L schematic, R51 connecting lug 3 to just after C54. There are a few component changes that would need to be considered (R_ks and pot values). I've the following questions intially: - How do I supply power to the new / existing stages? Can I run a connection from 'E'? Or do I add a resistor & cap (R60 & C53) and make 'D'? The former is easier! - Are the bright / fat selector and tone stack bypass more or less redundant? - Given the voltages indicated, would there be additional bias changes needing to be made to get a similar sound to the 'stock' L2L / HO? - Is the change in HO wiring described above a good idea? I like the idea of keeping the volume similar whilst OD increases or decreases (again, perfect for living room playing). Thanks for any advice!Thu, 27 Aug 2015 05:55:12 -0400 UberSEL PS - is it a regulated PS?(by Denny Gracey) I've been reading up on regulated power supplies, mostly in pursuit of minimizing noise in a my UHG build and of course expanding learning. I've found references on the forum to regulated PS schematics, but the posts are older and links to schematics in those posts are no longer active. The UberSEL PS looks interesting - definitely different than the SEL PS I'm currently using. Is it a regulated PS and/or will it generate less high freq noise, both radiated and ripple? I'd also be interested in studying other PS schematics for single ended high gain designs, so any links much appreciated. DennyWed, 26 Aug 2015 14:32:59 -0400 Parts selection for a new build(by GeorgeG) What brands do you guys like for: Caps Resistors Pots Switches Transformers That will result in a good sounding build without wasting money chasing the last 5%? Thanks, George Wed, 26 Aug 2015 14:26:17 -0400 Short "How Tubes Work" Video(by robrob) I edited and annotated the original 1943 film "Electronics at Work" to create a 3.5 minute video that has pretty good animations which show how electrons flow through vacuum tubes to amplify signals and rectify DC: <a href=" " target="newwin1440871695">[link]</a> Wed, 26 Aug 2015 14:20:20 -0400 Who wants to run the kit business?(by Chris Hurley) Hi Folks, I'm looking for someone to take over the AX84 kit business. I haven't had time to focus on it for a while now and I think the time has come to shut down the Doberman end of things. I'd like to work out something where kits can continue to be available though, if I can find the right person to take it over. If you're interested in talking about it, send me an email with your thoughts. Best regards, ChrisWed, 26 Aug 2015 13:04:41 -0400 EL34 Screen voltage(by tooltime) My past few 2xEL34 amps I have built are running plates at around 475V, and the screens around 470. I was looking at the JJ datasheet and it says limiting values are Ug0 = 800V and Ug = 450V. Can someone explain the difference? Am I stressing the tubes too hard?Wed, 26 Aug 2015 07:58:37 -0400 a Queen covert from the good old days(by Kursad K) <a href=" " target="newwin1440871695">[link]</a> circa 1994, a mostly unknown all-female cover band from Istanbul, and 2 years later it was discovered by large music producers and started sounding like this <a href=" " target="newwin1440871695">[link]</a> and the singer became a major star in her country. That's what they call 'investment' I guess, like buying the stocks of a small company and watching them grow exponentially in just 2 years. Kursad Wed, 26 Aug 2015 05:09:42 -0400 5F6A-M Bassman Micro(by robrob) This is my latest micro amp project, the Bassman Micro tube guitar amplifier. It's a compact, moderately easy to build, three tube, 3 to 5 watt output practice amp (around 3 watts with a 12AU7 power tube and around 5 watts with a 12BH7). The Bassman Micro's single channel preamp circuit was inspired by the 5F6A Bassman's Bright Hi channel. The Marshall JTM45 preamp is an exact copy except for the use of a 12AX7 in V1 so this amp could also be called the JTM45 Micro. The Bassman Micro features two stages of gain, a tone stack buffer, a cathodyne phase inverter and a true push-pull power amp. More inof on the Bassman Micro: [url] <a href="[/url] " target="newwin1440871695">[link]</a> [img] <a href="[/img] " target="newwin1440871695">[link]</a> [img] <a href="[/img] " target="newwin1440871695">[link]</a> I'm a big fan of the 1950's Fender tweed amps and the 5F6A Bassman is a legendary amp that was copied by Marshall and became the foundation of that company's amp lineup so I decided design a Micro version of the Bassman. I used an almost exact copy of the Bassman's preamp and paired it with a cathodyne phase inverter and small bottle push-pull power amp. Why a cathodyne PI? Because I didn't need the extra gain of the Bassman's long tail pair phase inverter and the it would have required another tube. The greatest weakness of the cathodyne PI is if driven too hard it can develop nasty double-frequency distortion. I use a pre-phase inverter master volume paired with a 270k phase inverter grid stopper resistor to eliminate double-frequency distortion. I liked the output and flexibility of the 12AU7/12BH7 tubes for the true push-pull power amp. The 12AU7 with both triodes in push-pull will develop around 3 to 4 watts of output power. Swap in a 12BH7 and the output increases to 4 to 5 watts. My H&K Tubemeister 5 uses a 12BH7 in push-pull and it sounds very good. The 12AU7 and 12BH7 tubes are very similar in output tone but the volume boost from the 12BH7 is noticeable. Both tube types are readily available with the 12BH7 going for about $5 more than a 12AU7. One of the reasons I chose to use the Fender 5F6A tweed Bassman preamp in this project is the Marshall JTM45 uses an exact copy of the circuit except Marshall calls for a 12AX7 in V1 instead of the Bassman's lower gain 12AY7. All that's required to convert the Bassman Micro into a JTM45 Micro is to put a 12AX7 in V1. A 12AX7 in V1 gives you much more overdrive and pushes the Bassman Micro's tone into the 1960's. I installed the Bright/Normal Channel Switch because the only difference between a 5F6A's channels is the Bright Cap. By putting it on a switch you can choose between the two Bright and Normal channels. The Negative Feedback Switch allows you to disconnect the feedback loop and get a grittier, more 5E3 Deluxe type tone with earlier breakup, or turn on the feedback for the standard Bassman tone. I went with a 82k feedback resistor because the 5F6A used a 27k resistor with a 2 ohm speaker tap. To get the equivalent feedback from my 8 ohm speaker tap the resistor must be bumped up to 56k. Use a 39k resistor for a 4 ohm speaker tap and 82k for a 16 ohm tap. Feel free to adjust the feedback resistor value to your liking or even install a pot to vary the feedback but I'd use about 12k as the minimum feedback resistance (12k resistor in series with a 100k pot). The Tone Stack Bypass Switch is an easy mod that removes the signal sucking tone stack from the circuit. The signal will be 'boosted' when the tone stack is bypassed. The EZ81 rectifier tube uses a standard 9-pin socket and 6.3V filament heat so no 5V power transformer output is needed. If your power transformer does have 5V available and you'd rather use a standard, full size 8 pin rectifier tube like a 5Y3GT then just wire the 8 pin socket with the HT to pins 4 and 6, 5V heater lines to 2 and 8 and the B+ power line to pin 8.Sun, 23 Aug 2015 04:43:15 -0400 How safe is cloth covered push back wire?(by Alva Goldbook) Ever since I first used cloth covered wire, I've loved the stuff. I've always found stripping plastic covered wire to be quite tedious, and I've always loved the look of cloth covered wire. I've put the stuff in a few guitars, but I've always been afraid to put the stuff in an amp. I figured the stuff could catch on fire. But I've noticed that there's plenty of old Fender amps out there that still have their original cloth covered wire, and they don't seem to catch on fire. Is the stuff really safe to use in an amp with all those high voltages?Sat, 22 Aug 2015 18:19:23 -0400 Opinions on post PI MV.(by Alva Goldbook) I wanted to get everyone's opinion on PPIMVs. Do you like them? Hate them? I've never used an amp before that had one and I was wondering if they sounded better and were more User friendly than standard MVs. Are they problematic in amps with a fixed bias and NFB?Fri, 21 Aug 2015 16:56:36 -0400 Is there a way to drive or excite a small plasma globe using aud(by CChurchill) I'm really just investigating an idea to use a small plasma ball in my head cab as an indicator lamp, using audio signals for visual effect. You might be wondering why I would go through all the trouble of having to integrate all the needed circuitry, the added cost(etc.), all for a glorified "on" jewel lamp. Well, I think it could look cool and I like learning new things. Now, I'm not proposing that I drop a commercially available globe in the middle of my amp chassis and call it a day. That would look ridiculous, cheap, and gaudy. I was thinking about something small, subtle, and distinct. Having said that, I admit, I don't have any background in high frequency/high voltage circuits or flyback power supply designs, so on and so forth. Plus, I have some concerns that this may look cool, but would invite major problems in a guitar amp that really make it unrealistic. Namely, very noisy circuitry, high voltage arcing, and massive interference caused by the electric fields generated near sensitive high gain, high impedance signals. I bring it up on this forum because, well, it never disappoints- The knowledge pool is deep and I'm calling on you hardcore science enthusiasts, who never let a perfectly good high voltage supply go to waste and wind your own Tesla coils, or build Rife beam ray tubes. This idea was influenced was probably influenced by two things. The first was experimenting with LED biasing in the output stage of my amplifier and finding it interesting to see real time, fairly drastic, visual indications of how the output tubes transitioned from small signal level to full drive while actually playing in real time and not relying on a signal generator under test. Nothing ground breaking there, just interesting to "see" it that way. The second, is a local start-up company from here in the Boston area, called oneTesla. They developed a line of DIY "musical" Tesla coil kits. Their coils are controlled by midi commands sent from files on an SD card or a midi keyboard. The midi files feed an interrupter which receives an audio frequency command and feeds the resonant pulses which generate the sparks at the audio frequency waveform peaks (I would imagine analogous to a square wave peak?). I love the idea of it and it is a cool experience to see a tesla coil spark playing the Mario Bros. theme, however, the actual sound generated is almost unlistenable to me. Because of my concerns about using traditional plasma globe designs which I've listed about, I did some searching and came across something cool and different. This is a project where a guy turned a nixie tube into a plasma ball. see here: <a href=" " target="newwin1440871695">[link]</a> and here: <a href=" " target="newwin1440871695">[link]</a> This is small, doable, and creative. Is there any way of exiting the plasma using audio signals as a apposed to touching the surface?Fri, 21 Aug 2015 15:17:32 -0400 1x12 speaker cab(by epaoletta) I've finished my first build. It's a AX84 SEL. Works excelent in a chinise speaker... I want to make a speaker cab for a Eminence Wizard. I was about to start with the 1x12 speaker cab that AX84 design. But I read in the Wizard specifications that it has not data with a vented cab. Has someone tried that configuration? What are your recomendations? Thanks in advance. Excuse my poor english. Thu, 20 Aug 2015 05:53:58 -0400 Bias Question(by SX4Amps) I have a 20W PP power amp with a Lead Preamp. I have been experimenting with different sets of 6V6GT tubes and noticed that some of them that I would like to bias a little hotter (not more than 70%) but I run out of room turning the bias pot. I am using the 50k pot which the schematic calls for. Would I need to lower higher the value of R9 or lower or higher the value of R10 room get more room on the pot? Wed, 19 Aug 2015 10:03:47 -0400 How linear are tube rectifiers?(by Alva Goldbook) I realize this topic has been covered before, but I was thinking about taking some new approaches to it. The idea is to accurately simulate a tube rectifier with solid state parts. Typically this is done with a lowish wirewound resistor after the solid state rectifier. But resistors are linear, and tube rectifiers are not. As I understand it, lower frequencies require more current to drive speakers, so when you play a lower note on a guitar, the tube rectifier has a harder time providing the necessary current, and you get a compression effect on the lower notes of the guitar. Would it be possible to split the B+ supply into two paths, in which you'd add an extra filter cap that would need to be charged, but only when the current demands are higher, thus more closely mimicking a tube rectifier? It would require, I think, that the cap would need to drain when the current demands were lower. Or am I simply over thinking this, and the same thing could more or less be accomplished just using lowish filter caps?Tue, 18 Aug 2015 00:05:47 -0400 Homemade Amp(by EPFahey) I found a homemade amp. Looks like the design idea was Twin Reverb, blackface era. 4-5881s. I recapped the pwr supply and changed out the screen and control grid resistors. Same values. It distorts at low volumes, and all volumes. I researched biasing, and found that the plate dissipation on the power tubes was around 9.00 watts. The recommended PD is 16.1 watts [70% of 23 watts, from tube data sheet]. It is biased cold; and I cannot seem to raise it. I am reading -30V on pin 5, the control grid. How to lower grid bias or raise plate dissipation? Ther is a bias pot, but the range of negative voltages on it will not go lower than about -36V. I drew a diagram, if anybody wants to look at it. The date codes on the Xformers are 1959.Mon, 17 Aug 2015 11:50:39 -0400