AX84 BBS New Threads as of Sun, Sep 21st, 2014 @ 02:05:07 http://ax84.com Amp Parts and KitsDoberman Music Products, LLC offers a variety of parts and kitshttp://shop.dobermanamps.com My Mesa Mark-style preamp build(by EeroNiemela) Hi, I just completed my latest build, a Mesa Mark II C+ -inspired tube preamp. The original idea is by bancika, who also posts here from time to time, this is his site: <a href="http://diy-fever.com/amps/mesa-mark-iic-pcb/ " target="newwin1411279508">[link]</a> Anyway, I wanted to try making my own turret board layout as well as implementing a footswitchable graphic EQ. Here's my build: <a href="https://dl.dropboxusercontent.com/u/66888777/mark2/2014-09-18-1313.jpg " target="newwin1411279508">[link]</a> The front panel has switches for deep and bright modes above the pots, the other LEDs are a dual colour green/orange for clean/crunch and a red LED for EQ. Both clean/crunch and EQ are footswitchable. Guts: <a href="https://dl.dropboxusercontent.com/u/66888777/mark2/2014-09-18-1312.jpg " target="newwin1411279508">[link]</a> Still some cosmetic stuff to do, I will add an aluminum front panel, need to paint the baseplate and attach some rubber feet, maybe wood side panels... I also seem to have some pots in the tone stack working backwards, I have already rewired them once but I might need to ask for help with that one :) Anyway, sounds very nice, definitely sounds like a Mesa. Currently running it into the fx-loop return on my High Octane I built a few years ago. Sat, 20 Sep 2014 15:37:27 -0400 http://ax84.com/bbs/dm.php?id=486328 Free Backing Tracks(by RickTown) Hey All, Occasionally, I'll be on youtube watching gear demos or song covers or lessons, and I'll often read questions in the comments asking where to get the backing tracks. I feel bad for all these poor "backing-trackless" souls, so this is the site I use. <a href="http://www.guitarbackingtrack.com " target="newwin1411279508">[link]</a> I love it. Keep in mind that not all backing tracks are created equal, but I've had pretty good luck finding very usable tracks for all the songs I've looked for. Are there any other good sources out there? Sat, 20 Sep 2014 08:38:39 -0400 http://ax84.com/bbs/dm.php?id=486323 PCB rev 4 sockets don 't fit(by DutchMarco) Hi all, I (at very long last) took to finishing my Ffly Rev 4 PCB build, and I discovered that the pins for the tube sockets don't align with the PCB-holes. Now, what I could do obviously, is 1) bend the pins on the tube sockets and try to make them fit, hoping they survive use of the amp. (without cracking/bending) - I'm not liking this option, too fussy to bend the pins, the right amount etc. 2) take the PCB and drill some holes for the sockets, then drop the PCB over the chassis mounted sockets, and create small wire bridges between pins and sockets. - also not really liking this option, risk of cracking seems a bit big to me. 3) source a copy of John Calhoun's PCB design file, redesign the PCB to use the same build style as in (2). Which would you choose? This seems like a reasonable supplier: <a href="http://www.custompcb.com/" target="newwin1411279508">[link]</a> Sun, 21 Sep 2014 02:03:52 -0400 http://ax84.com/bbs/dm.php?id=486315 Most complicated documented build?(by jlaustill) Anyone have any links to any seriously complicated builds people have done? I'm curious what people have managed to accomplish after building my own frankenstein amp :) . I've seen some 2 channel amps that people have built successfully, anyone ever seen a 3 or 4 channel? I saw one kid claim that he built his own dual rectifier, but his only evidence was a grainy video, so I'm not convinced it wasn't just a really beat up one he put in a new box lol. I look forward to any and all neat/complicated/odd/whatever things you may know about :)Fri, 19 Sep 2014 19:08:10 -0400 http://ax84.com/bbs/dm.php?id=486313 Anyone have experience building a Gainclone?(by Darren Porter) I am thinking of building a Gainclone solid-state stereo power-amp. I've found plenty of workable schematics but I am having trouble finding a power transformer for a reasonable price. Any suggestions? Thu, 18 Sep 2014 07:09:30 -0400 http://ax84.com/bbs/dm.php?id=486310 PT orientation (by cameron nicklaus) I'm beginning a PR clone build. Got my chassis from weber and my PT from classic tone, I literally held out only one tiny tiny small hope that the mounting holes would match but of course they do not ;) my question is this...can I rotate the PT 90 degrees and drill new holes with out concern of the field causing trouble...or does anyone have a better thought on how to mount? Wed, 17 Sep 2014 18:50:33 -0400 http://ax84.com/bbs/dm.php?id=486308 Problem with JTM 30(by orkell Gujnsson) Hi guys. I have a Marshall JTM 30 on my desk that I have bin troubleshooting. First it was lacking power. I tested all the 12AX tubes and they were ok. I change all the sockets because they were not looking good and still it was lacking power. But all of a sudden I had power but a lot of hum. I took all 12AX7 tubes out and it stopped. When I put the face inverter back in the humming starts again. So I check the voltage on the tube. Then I see that the grid has abought 50v and the cathode has about which is of course not right. When I take the tube out the voltage on the socket pins measures ok? I have unplugged the signal path from the ton control. So I do not understand where this voltage come from except somehow trough the tube? I have switch the tubes but the problem is the same. Please advise. Best regards Mr Thorkell Gudjonsson Wed, 17 Sep 2014 11:49:07 -0400 http://ax84.com/bbs/dm.php?id=486300 5f1 OT noise(by Mcilfilm) Finished a 5f1 build. Pretty much the standard circuit, point to point on turret strips. The only difference is the that the I made is kinda small so the power caps/resistors are on the pt side of the chassis and the rest is on the other side near preamp. Tracked down a humming noise by re-routing some grounds and now it is quiet to the point that I have to put my ear to the speaker at full volume to tell it is on. Not bad, EXCEPT................... There is a crackle/static noise that intensifies when I move/wiggle the OT secondaries. I can get them situated in a way that they are quiet but any movement causes crackle/static noise. i can poke around anywhere else and no noise but when I move these it makes noise. I unscrewed the OT and tried different positions and I can increase the hum but can't effect the static. All of the power grounds are on a lug of the PT. Preamp and sound grounds to chassis. The pot is an alpha 1M audio. Your thoughts are welcome Thanks. Rob Wed, 17 Sep 2014 06:44:56 -0400 http://ax84.com/bbs/dm.php?id=486292 Light bulb limiter(by Darren Porter) OK, forgive my possibly stupid question, but... I really should build a light bulb limiter. So far I have been pretty lucky with my builds and their initial start-ups and fuse-blowing has not been an issue for me. My quandry is this... how do I build one seeing as how incandescent bulbs are now banned and fluorescent bulbs won't work? Could it be done with LED's somehow? Sat, 20 Sep 2014 05:50:56 -0400 http://ax84.com/bbs/dm.php?id=486291 fixed to cathode switch in PR clone(by cameron nicklaus) I'm about to get started on this one and I thought I'd put the switch in, I'm wondering if there's a way to keep the bias trem working in cathode bias mode. any thoughts? seems to me that the cathode bias will have current through it, so just connecting the oscillator circuit won't work. But maybe disconnecting the fixed bias voltage, then grounding the osc circuit but leaving it connected to the grid might do it? I've built a few amps but am a relative novice. Tue, 16 Sep 2014 10:05:18 -0400 http://ax84.com/bbs/dm.php?id=486283 I NEED an NOS 12ax7(by GeoMan) So here's my situation. My buddy gave me a really old Supro 8 to look at and see if I could fix up. Since he was waiting to come up with the spare change for the parts I had it in a closet in my spare bedroom. One night during a thunderstorm my dog freaked out, ran into the closet, knocked over the amp, stepped in it, and broke the pre (12ax7) and power (6v6) tubes. Now obviously i have to replace these tubes and i feel like they need to be vintage since they were vintage. I have a supply of old 6v6s that I recovered from a radio station, but no 12ax7s. Before I run off and pay internet price for one, I was wondering if anyone here might have one they'd be willing to swap for some NOS 6v6s. If so, reply and I'll get you an email address so we can work something out. Thanks PatrickTue, 16 Sep 2014 02:18:18 -0400 http://ax84.com/bbs/dm.php?id=486269 Biasing for a KT88(by Asa Patterson) I decided to install the variable cathode bias mod for the P1Ex so I could use a KT88 for the output tube. I'm getting 410v on the plate and the PaMax for the KT88 seems to be 42W. (The tube bias calculator on the site uses 35W, dunno why). Plugging those values into the formula given on the Variable Cathode Bias Mod Page: (42 * .9)/410 I get .092mA. The problem arises when I actually go to bias the tube. Turning the bias pot, the max and minimum values I get when measuring across the test points are .037v and .02v respectively. If the max at .037v represents 37mA, that seems way too cold doesn't it? Any help would be greatly appreciated, thank you!Sat, 20 Sep 2014 03:37:34 -0400 http://ax84.com/bbs/dm.php?id=486250 he Pink Floyd Tribute Show (2011)(by Kursad K) <a href="http://www.youtube.com/watch?v=qYbm096uzEc " target="newwin1411279508">[link]</a> I don't know who these guys are, but seems to be really well played. KursadFri, 19 Sep 2014 13:32:18 -0400 http://ax84.com/bbs/dm.php?id=486246 Blackstar Gem or Not?(by Douche Baggins) Purchased this amp a few weeks ago and linked a noodling/demo: <a href="http://www.youtube.com/watch?v=am7lBh8eyao#t=390 " target="newwin1411279508">[link]</a> . Like to get opinions about it's tones. Sun, 14 Sep 2014 19:12:10 -0400 http://ax84.com/bbs/dm.php?id=486243 Quetion about octal option(by lentzell) Hello all, this is my first post. I have a background in electronics and audio and could possibly do the math myself, but I'd like to make a quick question: Why the cathode resistor for the EL84 alone is 130 ohms, and when both sockets are connected in parallel with the option implemented, turns out to be 220 ohms?. This is actually good for a 6V6 with roughly the anode voltage given, I believe, but since the two sockets share the cathode circuitry, doesn't it change significantly the bias point for the EL84? The two tubes, of course, are never to be used at the same time. Thanks in advance.Sun, 14 Sep 2014 11:48:29 -0400 http://ax84.com/bbs/dm.php?id=486231 bad 120Hz hum on 18-watt build(by Darren Porter) OK I finished my 18-watt build last night and I can tell I am _really_ going to like this amp BUT I have a really bad 120Hz hum. I don't have a scope but I think it's 120Hz based on comparing it by ear to a generated 120Hz signal. The level of the hum is affected by the volume, tone and VVR control. With the volume all the way down, I get no guitar signal but I still do get a slight hum. It is VERY loud with the VVR and volume cranked. Things I've tried to fix it (none made it better or worse)... - I elevated the heaters' center-tap to the cathode of the power tubes. (I make this connection directly off of the pins 3, and not between the Rk/Ck and ground, correct?) - I ran shielded wires to the input jack/V1. - I replaced V1 with a known good 12AX7. - "Chopsticking" around inside. - I fixed an "iffy" looking solder joint at one of the heater connections. What is the 6V lantern battery trick? If I run my heaters off of it instead of the AC supply and it goes away, does that mean my heater wiring is bad and I need to re-do it? Hoping I can try some easy things before I start figuring out where to post some gut-shots... It's a Lite IIb build, FWIW.Sun, 14 Sep 2014 20:34:09 -0400 http://ax84.com/bbs/dm.php?id=486228 Thrift Store Find(by boblove) Was in the salvation army store yesterday and stumbled across a hammond m3.... No price on it, no reverb unit on it either. Looked like the lower photo in <a href="http://www.organforum.com/forums/showthread.php?12673-Hammond-M3-amp-question! " target="newwin1411279508">[link]</a> I couldn't stop thinking about it. The back was off and could see the tube recto and a pair of 6v6's. I don't know if it worked but was really intrigued to the point of dreaming about it... Worth picking up? For what price? Like I need another project....and I don't have the room either...I guess thats what my storage unit is for huh.Wed, 17 Sep 2014 12:20:29 -0400 http://ax84.com/bbs/dm.php?id=486224 power transformer for reverb(by Narciso Fiore) Hi guys, very pleased to be here once again!!0About two yeras ago you helped me very kindly with my first building: an hi octane amp (with octal tube and variable bias mods). I'm very proud with the amp but now I'd like to add a reverb tank. Actually I'd like build a new HO with such a feature. I've found a simple mod that picks up the audio signal from OT (low impedance) to feed the reverb tank and requires a 12ax7 tube to recovery the reverbered signal. The mod can be found at charlestonarea.com, it has been realized and a couple of demos is available. Now, I've a question on the adding the third 12ax7 tube to the amp: taking into account (theoretically, with octal tube mod) 300+300+300+1500 mA as current consumption at the heaters and 1.2+1.2+1.2+100 mA for the plates consumption, I think I need a power tranformer that can supply,say, 3A for heater secondary and 125mA at power rail secondary. if I'm not wrong.... In this case I think the hammond 369ex (universal primary) is no more sufficient. Any idea on a good substitute (I think I'll be able to find only hammonds)? ....or I'm wrong? thanks in advance ps: sorry for my poor englishMon, 15 Sep 2014 22:20:04 -0400 http://ax84.com/bbs/dm.php?id=486210 Ugly distortion on power amp/clean setting(by foulowl) Hi folks, I've been pulling my hair out on this one. Nothing fancy, just a p1 preamp into a Marshall/Fender long tail PI, into a 6x6L6 push/pull Marshall style power amp. Getting really ugly distortion at high volume. It sounds like a fuzz pedal. I have rebuilt the preamp a total of three times, looks like that's not the issue. I pulled the cathode caps off the preamp too to try lowering the distortion, no luck. I have checked the power supply, power amp, and PI a number of times but haven't found anything. I have swapped the power and preamp tubes as well. Finally, I have also tried pulling all but one pair of the power tubes. I feel like maybe something is wired incorrectly in the PI or power section and I've just missed it. Not sure what I can measure for more clues. I do have a scope. Thanks!! Sat, 20 Sep 2014 03:44:48 -0400 http://ax84.com/bbs/dm.php?id=486205 Proposed Solution to Impedence mismatch(by boblove) I'm looking for some feed back on an idea I have for using an extension cabinet. I'm currently using a single 12 in 16 ohm speaker in a combo amp and I'm looking to us an extension cabinet. My current problem is that the extension cabinet really needs to be 16 ohms as well but I've only 8 ohm cabinets right now. What about using an intermediate box to increase the load resistance like <a href="https://www.flickr.com/photos/117798883@N05/15014169647/ " target="newwin1411279508">[link]</a> as a temporary solution until i fabricate or purchase a 16 ohm cabinet. Its hard to see in the link but thats supposed to be an 8 ohm 50 watt resistor in the box. 1. Will it work without damaging my OT ? 2. Will it sound okayThu, 11 Sep 2014 09:24:20 -0400 http://ax84.com/bbs/dm.php?id=486194 rectifier voltages question(by Darren Porter) Hey all. My current build is an 18-watter with VVR and I have wired the PT up but I am not sure if the voltages I am getting are correct... Everything looks good except for the heater voltages on my rectifier socket. With NO rectifier plugged-in, I am getting 9.1 to 9.4 volts across the pins for the heaters. (FWIW, the rectifier will be an EZ81, so it's pins 4 & 5.) Will this drop to normal once the rectifier is plugged-in? I don't want to risk blowing-up the tube with 50% more than it's rated heater voltage! Again, there is NO load to the socket at all... NO rectifier plugged in and I have NOT wired-up the post-rectifier filter network or the VVR. Thanks! Wed, 10 Sep 2014 03:27:35 -0400 http://ax84.com/bbs/dm.php?id=486182 Merlin's new curve tracer design(by Ardencaple) As usual, a concise and interesting project description from Merlin: <a href="http://www.valvewizard.co.uk/curvetracer.html " target="newwin1411279508">[link]</a> There are some other interesting curve tracers out there. Merlin links to the u-Tracer, which is well regarded (a friend of mine has one, and rates it) [ <a href="http://www.dos4ever.com/uTracer3/uTracer3.html] " target="newwin1411279508">[link]</a> There is also this idea, which uses a PC sound card to capture the I/V values, and also to generate the grid levels: <a href="http://www.dmitrynizh.com/plate-curve-tracer-acpc.htm " target="newwin1411279508">[link]</a> Merlin uses a Supertex LR8 high voltage regulator in his design, and notes that they are almost impossible to source in the UK. I bought a couple from Tube-Town with my last order. They are in Germany, but I have found them to be very good on delivery, and not too expensive. Sat, 20 Sep 2014 03:14:24 -0400 http://ax84.com/bbs/dm.php?id=486168 Can the PT Take It?(by turtle441) Question regarding selecting an appropriate PT for a project. I'm working on a homebrew 2-channel amp, current plan will require 4 12AX7's, plus 2 EL84's running push-pull and a tube rectifier. I've built a couple of small kits before, but this is my first stab at putting together the pieces to design my own. Big question is, is there any formula/calculation I can use to figure out whether a particular PT would be adequate for the amp? I'm looking at a Heyboer 18W set that I think would work. Looking at the # of amps drawn by the heaters, it should be able to handle the load with a 10% safety margin. But, I haven't been able to find any calculations to figure out if the high voltage secondary's up to the load. Do I need to worry about this?Tue, 09 Sep 2014 04:31:01 -0400 http://ax84.com/bbs/dm.php?id=486163 radial or axial(by clints) Any opinions on board layouts for axial vs radial? I have some radial 47uf 450's from a previous build i could reuse. Thu, 18 Sep 2014 14:12:32 -0400 http://ax84.com/bbs/dm.php?id=486157 Tube identification(by Rudder) What is the easiest way to identify tubes if all of the markings have been rubbed off? I believe there are some form of bath numbers on, but I can not seem to find anything that actually identifies the tubes from them.Mon, 08 Sep 2014 04:22:39 -0400 http://ax84.com/bbs/dm.php?id=486128