AX84 BBS New Threads as of Tue, Mar 03rd, 2015 @ 12:51:56 http://ax84.com Amp Parts and KitsDoberman Music Products, LLC offers a variety of parts and kitshttp://shop.dobermanamps.com Crossover distortion at all power levels(by foulowl) Hi folks, Seeing this output from my 8 ohm tap at all power levels: <a href="http://i.imgur.com/EQpO3n7.png " target="newwin1425405117">[link]</a> Function generator is running at 4 khz, but same problem at 400 hz as well. Output from PI is a perfect sine wave. Amp is push-pull 6x6L6. This is with bias set at -61.7VDC, _and_ same issue at -43VDC. (An additional item of note, the bias voltage seems to have no effect on speaker output shape or power.) Bad tubes perhaps? I'm at a loss. Thanks!Tue, 03 Mar 2015 07:02:03 -0500 http://ax84.com/bbs/dm.php?id=489418 New 4-4-0. Thanks!(by johnnyreece) Hey, guys! I wanted to let you know that I've recently finished a new 4-4-0 build. It's mostly stock, except I've used two 6J5 tubes instead of a single 6SN7, and I've used a full-size Trainwreck style chassis to put it in. Wow, it's a little monster! I'm thinking I may try to modify it to have a little less gain. I'm using a 12AV7 in the PI position, and a 12AY7 in V1. I typically play humbucker guitars, and, even turning the volume knob down on the guitar, there's a lot of gain on tap. I did have to modify the bias circuit a touch in order to get in range. I'm still a bit out, but it's close enough for half my stash to work within limits, so that's good. I really just wanted to stop in and thank everyone for all the effort put into this! This site has been a wonderful resource for my recent foray into 2w amps!Mon, 02 Mar 2015 22:14:16 -0500 http://ax84.com/bbs/dm.php?id=489409 Oscilloscope (purchase guide)(by Kevoid) I've been otaining tools, doing a few projects here and there, and fixing/repairing amps, etc. I am now ready to start my first tube amp build. Almost that is. I do want to obtain an oscilloscope and get some pratctice on it first. I work on guitars, bass's, solid state amps, tube radios and amps, effects pedals, etc. I would like to obtain a good that I won't have to upgrade later if possible, but I also can't be shelling too much $$$ on it at the same time... So, any guidance would be much appreicated. P.S. - I finally got an ESR meter. For those about to rock buy one earlier rather than later, you won't reqret it ;)Tue, 03 Mar 2015 09:06:51 -0500 http://ax84.com/bbs/dm.php?id=489408 Project Mix octane da(by Odilon) Hi guys, I heve spent some time around a good amplifier for my guitar. FOUND. But since I have some experience in electronics (not tubes) I tried do build something diferente: A Hight octane preamp, a daysicutter inversor and a daysicutter power with 2parallel El84. I alredy did 3 separetes PCB: 1)pre ; 2)inversor and 3)power The power supply is still in developments. Any opinions??? Mon, 02 Mar 2015 17:17:06 -0500 http://ax84.com/bbs/dm.php?id=489405 High gain single ended(by jonny bailey) Hey guys, new to the forum. I have a question, of course......has anyone married the high gain or ultra high gain preamp in the last chapter of blencowe's second ed. book with a single ended output stage? Does the SEL II sound close? Does the uber SEL sound close? I have built PP amps, but was wanting a smaller high gain practice amp to crank at home and still have a killer tone without slamming the front end with a pedal. Any input would be most helpful. ThanksMon, 02 Mar 2015 21:14:07 -0500 http://ax84.com/bbs/dm.php?id=489404 resistor choice.(by Dan Moos) I have never really considered resistor type choice, but now I feel it's time to get a bit more into component selection than I have been. In all my builds, I have been using two watt metal oxide throughout. Reason? Two watts is more then enough margin in most of an amp, and AES sells a handy kit with a full assortment. My understanding is that metal oxide is not ideal for audio. Metal film and carbon film seem to be available in kits of 1/2 watt assortments (yes, I like kits.) My question is, are metal oxide resistors that bad, and what exactly is the bad sound they have? I am leaning towards metal film if I make a switch, but am willing to hear the arguments for carbon film. I have no interest in carbon comp. Also, since metal film/carbon film come in 1/2 watt, how much margin is considered acceptable wattage wise in a quality amp? Tue, 03 Mar 2015 11:11:54 -0500 http://ax84.com/bbs/dm.php?id=489396 Anyone built Brian's L2L?(by Denny Gracey) I just finished Brian's L2L SE based on the original schematic posted here; did a bit of thread searches today and discovered that original schematic was prototype and Brian and others have made changes since (e.g. moved tone stack to follow 4th stage), but I can't locate an updated schematic. If anyone has built an L2L, let me know. Thanks! Mon, 02 Mar 2015 20:57:31 -0500 http://ax84.com/bbs/dm.php?id=489384 Check Schematic and Power Supply Questions(by turtle441) Hey guys, working on my first amp design/modification. Prior experience is with "paint by the numbers" type build. Basically, the amp uses a switch to make a 2-channel amp by using 2 different tone stacks. Was wondering if you guys could take a look at my schematic, as well as answer a few newbie power supply questions. Schematic's here: <a href="https://dl.dropboxusercontent.com/u/110475524/SL%20Combo%20for%20AX84.bmp " target="newwin1425405117">[link]</a> I think I've got everything in the design pretty much ironed out. There's one coupling cap value (C2) that I'm going to have to experiment with (the 2 production amps I based it on had 2 different values, where it was relative to the switch, I didn't have a good way to have 2 values) and I'm going to play some with the power filtering node to the power tubes as it seems like there was some controversy online about exactly how that was done. Now for the questions: 1. Fusing the high voltage secondary - I've seen a couple of posts here advocating doing this, either by putting fuses on the secondary leads, or by putting a fuse or resistor on the center tap. How are you doing this from a layout standpoint, mounting fuses next to the rectifier? I haven't seen this in the schematics of production amps that I've looked at (admittedly, mostly older ones), so I wasn't sure how it was usually implemented. 2. Standby switch - All the schematics that I've seen for the amps this was based on don't have a standby switch. I checked the manufacturer's website, appears the production models don't either. In doing some reading on Merlin's website, he makes a pretty good argument that if you've got a tube rectifier, it's unnecessary. How are you all handling this now days, do you not use standby? Have any of you implemented Merlin's suggested solution (the 1-2W resistor in parallel with the standby switch)? Right now I'm leaning towards no standby, but was curious as Merlin's solution was a new one to me. 3. Extra stuff on the rectifier - This one doesn't pertain to my schematic... yet. I've been researching some different schematics and layouts for the spitfire and lightning online. Looking at the ceriatone's layout (not posting a link as I'm not sure what the rules are... it is freely posted on their website but I know admins are strict about that stuff here). There's a couple of extra parts strung on the GZ34 rectifier. 2 Diodes running from pins 6-7 and pins 4-5. I'd read in Weber's book that he suggests something similar as a failsafe should the rectifier fail, so I'm assuming that's what that is. But, then, they also show a 0.01uF 3kV cap strung between pins 6 and 4. What the heck does that do? Sun, 01 Mar 2015 11:56:43 -0500 http://ax84.com/bbs/dm.php?id=489379 Burning?!(by winghamwill) Hi, I have an SEL, and whe I am using it it gets a strong smell of burning. It outputs a lot lower than it used to, it plays exactly the same but just a hell of a lot quieter. It has a brand new power tube in it. Through some hesitant investigation I have found a resistor and a cap that look like they have overheated and are probably causing the smell.... The 5k/5W resistor (r6in the diagram) and the 100uf 50v cap (c6) I have a feeling the resistor was burnt before I changes the tube because I know the old one was bad and had the same problem then. But I think the burning cap is new. I have just bypassed the tone stack and master volume by running directly from pin 3 on v3 (12ax7) to the 5.6k resistor before pin 5 on the power tube. Could this have caused the cap to burn out? Any ideas what couldn't have caused the volume drop? Final thing... When I put one if the gain pots up past about 9 o'clock, I get a very high pitched squeak. Is this normal? Bit out of my depth but trying to learn more all the time! Any help would be appreciated.Tue, 03 Mar 2015 12:35:30 -0500 http://ax84.com/bbs/dm.php?id=489374 Two More Questions About 1x12 Cab(by cpsmusic) Hi, Picked up the timber for the 1 x 12 cab yesterday. I have two more questions regarding the plans: 1. The front baffle and rear panels are recessed by 1/4 and 3/16 respectively. Any reason for the recess and also any reason for the difference between the two? 2. The timber I got for the battens is 40mm x 19mm. The carcase timber is 19mm thick. 60mm screws will be too long and I couldn't find any 55mm screws so I ended up getting 50mm ones. My question is, will these be long enough as only 10mm will go into the case? I guess glue will help here? As the cab is going to be covered I was thinking that dowels might be better and stronger? Cheers, ChrisSat, 28 Feb 2015 22:20:59 -0500 http://ax84.com/bbs/dm.php?id=489366 parallel wire(by JB Angelo) I don't have 600 volt wire for my power amp section, which is running about 475 at the plates. Is there any issue with twisting 2 300volt wires together in parallel? Will that cause an extra magnetic field around the wire which can induce noise? Thank you Sat, 28 Feb 2015 21:01:07 -0500 http://ax84.com/bbs/dm.php?id=489363 Troubleshooting HF oscillations using oscilloscope (by Denny Gracey) Just finished Brian's L2L. Works fine, cleans are nice, but with gain cranked suffering from HF interference (squeal). Had same issue with the SEL after removing the board several times for mods which weakened a few wires at their solder joints. I've likely got a bad solder joint on a wire somewhere, but before i pull the board and resolder, is there a way i could isolate the problem using oscilloscope? Fri, 27 Feb 2015 21:08:43 -0500 http://ax84.com/bbs/dm.php?id=489362 Amp Switching Circuit Popping(by 8Len8) I've get a Phaez amp that has 2 individual inputs, one for each channel. I decided instead of using an AB box that I'd install a switching circuit to route a single input to either channel. Originally the amp had each channel's preamp tube connected to its own input jack. I got a Granger optoFET channel select board: <a href="http://grangeramp.com/shop/index.php..._image&pID=493 " target="newwin1425405117">[link]</a> I powered it off a wall-wart and hooked it up like this (all connections via coax): 1 NC - ground 1 Com - clean channel 12AX7 cathode 1 NO and 2 NC - input jack 2 Com - dirty channel 12AX7 cathode 2 NO - ground My only problem is that I hear a slight pop when switching from the clean to dirty channel. I've read that FET based channel select circuits should have quiet switching. Is there a pull-down resistor or something that I'm missing that could be causing the pops?Sun, 01 Mar 2015 04:27:37 -0500 http://ax84.com/bbs/dm.php?id=489359 Gibson GA-55V build(by Brad Weeks) I found a copy of the Gibson GA-55V (true pitch shift vibrato based on the Wurlitzer circuit) in the Jack Darr (4th edition) guitar amps book. The vibrato mixer/modulator in the GA-55V schematic is different then Gibson's GA-83S vibrato amp and their GAV1 stand alone vibrato. Gibson has been known to have errors in their schematics and was wondering if anyone can confirm the GA-55V drawing as being correct? Thanks, Brad Fri, 27 Feb 2015 01:09:09 -0500 http://ax84.com/bbs/dm.php?id=489342 BIAS supply(by mategenomics) Hello guys. I am recently building a CERIATONE JCM800 2203 amp with non original transformers. I have 350V taps for HT, 6.3V for heating but just 40V available for biasing. Amp from which I took PT had integrated circuits so that is maybe the reason for such atypical voltage. My schematic needs 100V bias supply. Is there any schematic for suitable voltage multiplier for instance? And do I understand correctly that it doesnt matter for which currents is it built as g1 draws current in microvolt-magnitude? Thank you in advance!Mon, 02 Mar 2015 05:13:54 -0500 http://ax84.com/bbs/dm.php?id=489329 SEL - one knob(by winghamwill) Hi, I built an SEL a while ago and it died, not sure what happened to it, I tried a few things but haven't got to the bottom of it so it has been sitting alone for a while.... I have recently come across the Big Crunch one knob guitars and this has stirred me up so I thought... New project, get the SEL running as something similar and simple like the one knob. Any one have any ideas of how I could do this, would it be a case of ripping out the tone stages and bypassing the gain pots or a big overhaul? If anyone fancies altering a schematic I would forever be in their debt! Thoughts? Cheers WillWed, 25 Feb 2015 21:16:58 -0500 http://ax84.com/bbs/dm.php?id=489317 New Faceplate for FF (by Rico Delrosado) Hello, ax84! I've been lurking around here for a while, reading all the Firefly posts, but this is my first post. I just received my custom FF faceplate from Mojotone. I'm very excited. If I wasn't sick, I might be able to start work on it, but at least I'm able to buy parts. :) Anyway, if I can figure out how to post a pic, I will. You may or may not see a pic below. Stand by for lots of questions. RicoThu, 26 Feb 2015 11:04:39 -0500 http://ax84.com/bbs/dm.php?id=489313 19 rack ground loop problem(by jack plug) I need some information on how to hook up a 19 inch rack which contains a tube stereo power amp,a tube stereo pre amp and a lexicon reverb to avoid ground loops as the preamp and tube power amp are earthed or grounded via the mains plugs and also through the steel rack mounts. Also commercial jack cables have continuity through the screened portion of the cable. I'm thinking i should make up my on cable sets with one end of the screen disconnected so signal ground goes via the earthed portion of the supply. I'm also trying to work out how i can isolate the 19 rack units from the rack mounts to prevent a ground loop here.Wed, 25 Feb 2015 19:04:48 -0500 http://ax84.com/bbs/dm.php?id=489306 Want Fender Vaporizer Mods!(by Matt Whittingham) Hi guys, I'm modding my guitarist's Fender Vaporizer with new efficient speakers, to try and make it as loud as 12 Watts should be! On it's own this is a great upgrade but whilst I'm waiting for the new tolex to be fitted I'd like to modify the circuit. I have seen countless praise of the BillM mods for Blues Junior amps, and I'd like to try and achieve the same kind of results with the Vaporizer, the only problem is I cannot source a Schematic for it. I'd like to do the tone stack upgrade (Orange Drops) and the Power Supply Stiffening upgrade (bigger). How would I achieve these mods? And do you guys have any suggestions to make the amp sound 'bigger' and louder? :)Sun, 01 Mar 2015 10:48:13 -0500 http://ax84.com/bbs/dm.php?id=489305 Does anyone know where to find quick connects?(by Alva Goldbook) I've been having trouble finding these. I'd prefer not to solder onto the giant lugs of this power switch. Thu, 26 Feb 2015 10:14:08 -0500 http://ax84.com/bbs/dm.php?id=489297 Merlin Figure 12.10(by GeoMan) One of the things I've had trouble with is parsing schematics into real layouts. I've gone through the exercise of making a "layout" out of the parallel effects loop in Merlin Figure 12.10. <a href="http://i170.photobucket.com/albums/u256/mplesley/Merlin%20Figure12-10.png " target="newwin1425405117">[link]</a> I understand in broad brush strokes how it works. I know this isn't a proper layout, but if anyone has a minute, and wouldn't mind making sure that I've got all of the right things going to the right places, that would be awesome. Thanks as always. -PLWed, 25 Feb 2015 15:02:05 -0500 http://ax84.com/bbs/dm.php?id=489295 1x12 Speaker Cover(by cpsmusic) Hi, The 1x12 Cab plans don't give any indication of how to construct and attach a speaker cover (other than indicating that the speaker is recessed 1/4 inch). I'd like to protect the speaker with Fender-style cloth. Just wondering how other people have done this? I was thinking of using a wooden panel with a hole cutout for the speaker (in the standard way). I have two questions: 1/4 inch isn't very thick and with the thickness of the cloth (x2 if it wraps around the back) that decreases it further. Also, how should the speaker cover be attached to the speaker baffle? Cheers, ChrisThu, 26 Feb 2015 17:46:40 -0500 http://ax84.com/bbs/dm.php?id=489289 Westlabs transformer sets(by Henrik Reiersen) Hi all, New member, Henrik from Norway here. A few years back, I bought some transformer kits from a company called WestLabs, run by a person called Dave West. I haven't used them yet, but now I'm thinking of a new build. I tried to connect to the westlabs.com website but it's no longer in existence, and since the transformers didn't come with a wiring diagram, I no longer know how these babies are wired. According to Dave, these were left surplus after the Matchless factory closed the first time around. Did anyone here have the forethought to download the wiring diagrams for the westlabs 30 and 15w transformer kits before they closed shop? I appreciate any help. Kind regards, HenrikFri, 27 Feb 2015 09:58:23 -0500 http://ax84.com/bbs/dm.php?id=489283 BOM and Cutting List(by cpsmusic) Hi Folks, I'm new to the forum so sorry if this question has been answered before (I've done a search but couldn't find anything). Is there a bill of materials and/or a cutting list for the 1x12 cab? Cheers, ChrisTue, 24 Feb 2015 20:33:22 -0500 http://ax84.com/bbs/dm.php?id=489281 Transformer Help(by Jeph88) Any assistance on how this would be wired? Series? <a href="http://www.antekinc.com/as-2t300-200va-300v-transformer/ " target="newwin1425405117">[link]</a> Tue, 24 Feb 2015 00:14:56 -0500 http://ax84.com/bbs/dm.php?id=489275