AX84 BBS New Threads as of Fri, Aug 22nd, 2014 @ 02:12:57 Amp Parts and KitsDoberman Music Products, LLC offers a variety of parts and kits Hybrid 1 Watter (not mine)(by Douche Baggins) Did a YouTube search recently for 1 watt amps and this: <a href=" " target="newwin1408687977">[link]</a> is among many posted. Here: <a href=" " target="newwin1408687977">[link]</a> is the schematic/build link. Build pics: <a href=" " target="newwin1408687977">[link]</a> Cheers to nzCdog for the build, video and guitar chops.Thu, 21 Aug 2014 21:29:39 -0400 OT impedance match(by BaltorTinazli) Hi; I have an OT which has 18,4k primary impedance instead of 22.5k with 8 ohm speaker. Is it ok or any disadvantages with it? I have bought five sets of them 4 years ago to build fireflys. But i could start building it yet:) Voltage ratio is 1:48. Impedance ratio is 1:(48)=1/2304====>2304*8ohm=18,4k. It has center tap also. I have built HO,20WPP amps before. Great site great people.Thanks. BaltorThu, 21 Aug 2014 07:03:19 -0400 Dual Concentric 1 meg Pots?(by The Ballzz) Hi All, This is my first post, so please be gentle. I have searched for 1 meg dual concentric pots and found them to generally be made of "UNOBTAINIUM", however, I have finally found a source to have them manufactured in reasonable quantity at a fair price. I'm wondering if anyone, besides me, sees or understands the potential use(s) for such a pot? I have not yet placed my order and am exploring interest in any of these at a reasonable cost. This is not intended as a "for sale" post simply seeing if anyone would want a few of these if I were to acquire100 or so of these. If no interest, I will likely not make the investment. Thanks In Advance, Gene Thu, 21 Aug 2014 08:23:38 -0400 Passing the time(by Ken Graves) On my job I have to stay alert but there's not much activity for me. So, when I don't have a project going I need to keep my hands busy. So I bought some mild steel from Home Depot, some files and wet or dry and went to work. Since this is mild steel and can't hold an edge long I call it a letter opener. <a href=" " target="newwin1408687977">[link]</a> <a href=" " target="newwin1408687977">[link]</a> When my daughter in law saw it she asked if I could make a letter opener for her so . . . <a href=" " target="newwin1408687977">[link]</a> <a href=" " target="newwin1408687977">[link]</a> My next couple of tries will be with carbon steel to be hardened so they will be sure enough real Daggers. One will have a Rosewood handle, the next will use Bocote. Tue, 19 Aug 2014 15:41:07 -0400 P1 eXtreme transformer question(by aeronaut) Greetings, Has anyone played around with other transformers for the P1 eXtreme? Thinking of doing it for a first build, and it looks like one can get an Edcor CXPP30-MS-5K for about the same price as the Hammond 125ESE output transformer. The Edcor is rated at 30W, 20 Hz to 20 kHz, and has a 5k primary and 4, 8, and 16 ohm outputs. Seems like a lot more iron for the money, and rated to handle the bigger tubes the P1 eXtreme can take (perhaps a little shy for the KT88, but much closer than the Hammond's 15 W). Might be more than one needs, but for the same price, seems like a no brainer. Any concerns or potential problems? Or is the 30 Watt push pull rating the same as a SE 15 Watt because in push pull it only conducts part of the time? Even so, the better frequency response is still an upgrade, albeit perhaps not a useful one. Can't link it, but go to, menu bar class X, item push-pull. Seems to be way better value than the hammond tranny. Regards, Martin Tue, 19 Aug 2014 21:49:41 -0400 Help! How is this possible?!?(by tooltime) <a href=" " target="newwin1408687977">[link]</a> ^^Watch the video first. I am getting a hum/buzz that seems to come from PI area. It does turn down with volume, but I dont believe its actually coming from the preamp. The amp looks like a mess b/c I have spent many hours working on it. I have tried... -Physically moving OT further away from preamp -disconnecting the OT and temporarily wiring in another one outside the chassis so I could move it around to see if anything changed. -shielding signal wires -humdinger -new PT -all new tubes I don't understand what is causing the voltage to appear on the fiber board, this baffles me. How can a non-conductive material have an induced voltage?? But somehow voltage is being induced which I believe is the cause of the hum that I can't eliminate. This is a clean amp, I am using the LTPI as a mixer of the 2 preamp circuits (a 12AX7 channel, and an EF86 channel) I have built several of these with no issue. Any help is greatly appreciated, I don't have much hair left to pull out.Wed, 20 Aug 2014 10:37:57 -0400 Soldering to turrets(by David Staepelaere) Here's an old instructional video on soldering to turrets... <a href=" " target="newwin1408687977">[link]</a> It certainly has good information for people just starting out, but it also has a few details that might be helpful even for more experienced folks. Tue, 19 Aug 2014 22:27:42 -0400 Some questions before I build P1-eX(by JayWalker) Hey guys. I'm interested in building the P1-eXtreme amp, but I have some questions. I'm not buying a kit (I have many parts laying around) but I want to make sure the things I am buying will be suitable. I'm planning to use a 6L6GC power tube, will this OPT be suitable for B+ of around 350v (plus or minus, depending on power trans)? <a href=" " target="newwin1408687977">[link]</a> I ask because I'm still a little fuzzy on OPT theory, but I think 5k is almost perfect for this, right? With that transformer, the anode current would be 70ma for 24.5 watts dissipated @ 350v. The OPT says 15 watts rating, is that referring to max OUTPUT power or the max power that can be put through it? Should I go for a bigger OPT (or perhaps a higher impedance, as the case may be). The Hammond OPT specified for this project is also rated for 15 watts which makes me think it's OK. Given the above stated, what would the expected output power be? I've seen 50% of anode dissipation quoted, so maybe ~12 watts? I've got some other ideas but I'll start here to make sure I'm not getting ahead of myself. Any help is appreciated.Thu, 14 Aug 2014 19:45:23 -0400 67? Gibson Skylark (new project)(by Kevoid) It took a while, but I finally got an all tube amp project to work on. It's an old Gibson Skylark. Here's a link to one just like the one I have: <a href=" " target="newwin1408687977">[link]</a> It had a really bad hum and the 3 stage (10uf, 10uf, 20uf) filter cap values where way off. I change it out using 2 new NEC 10uf caps and 1 NEC 22uf cap. The 22uf cap read a little over 21uf so I figure it's within the percentage rating of a 20uf cap. Anyways, no more hum. NOW, comes the learning experience... It's really thin and bright sounding, but it's my understanding these amps came from the factory this way. I am hoping to get some help with understanding the tube biasing/pins used in this amp and just overall any thoughts/ideas to help me learn the most I can from/about this amp... I am still heading toward my goal of building my own tube amp(s) one day. But, for now, I am hoping to thoroughly understand this amp... Really looking forward to see what you guys have to say. I know this sight was great when I was working on the 90's solid state Princeton... Thanks again, KevinFri, 15 Aug 2014 17:17:35 -0400 Speaker wire from 120W head into 2x12(by dannyBwheeler) Hey builders. First post on here, I recently replaced an old cheap radioshack solder iron, and have discovered new things to fix with the newfound power of solder gun and a hakko fx. I've played through a friends AX84, and look forward to making one soon. Before I go off on that project, I should probably fix what I got. I've got a nice Ampeg SS140C combo, and one speaker cuts out more than it's in. Since it's almost 30 years old, I'm assuming it just needs to wire. It's a 1/4 phone to slide-ons +/- . Where's the best place to get wire? Each speaker is 4 ohms, and here's a link to the schematics if anyone needs it to answer the question: <a href=" " target="newwin1408687977">[link]</a> Thanks guys!Tue, 19 Aug 2014 05:52:03 -0400 Less work?(by steve25) I was on my way to get my hair cut today and on the way in the barber shop door I though to myself well, I am 59 now and half bald so should I not get charged half price for a hair cut? I mean it's half the work, half the sweep the floor clean up time right, or how about throwing me a bone on a shave or double up on slapping on that after shave stuff they toss on ya!Wed, 20 Aug 2014 20:16:19 -0400 Thinking of "Wreking" my SimplePre-20WPP(by Darren Porter) I saw another thread on here about converting a SimplePre-20WPP amp into a 4-4-0. After looking at the schematics, I see that they are very similar. When I built my Simple20 I even had the forethought to wire in two extra tube sockets just in case I wanted to add an effects loop and a 1-tube reverb, so I think this will be cake. A question though... I see the 4-4-0 has much lower voltages on the 12AX7's than the 20WPP design. Do I need to lower my voltages or will I be ok using them as-is? Would I need to adjust any values anywhere if I did leave them alone? How practical would it be to wire a switch in to make it a two-channel amp? Basically, a Deluxe and a 4-4-0 in one package? Or should I just wire-up a 4-4-0 preamp and feed my Simple20 either through the main input or through an effects loop return?Wed, 13 Aug 2014 12:46:45 -0400 Lower Watt 6V6/Octal Alternative?(by Douche Baggins) Looking to reduce output for my P1 without dropping plate voltage (275v. I know a 6K6 is one option, but I am hoping to get around 1 to 2 watts output in Pentode. I've tried several types(mU) of preamp tubes, but doesn't lower volume enough and effects distortion too much.Thu, 14 Aug 2014 11:33:19 -0400 Tip on installing turrets(by LincolnR) I'm working on a High Octane build and started installing turrets in my turret board tonight. Unfortunately I don't currently have access to a drill press except at work (can probably get away with it for drilling a few large holes like tube sockets, especially if I'm using my own bit, but not for a half hour while I stake 50-some turrets). Initially I tried just hammering them with the staking tool, but had the problem that the turrets would sometimes bend, or the upper part where you're supposed to wrap and solder components would start deforming. With a bit of experimentation I discovered something that works pretty well to address this: Take a socket (as in the kind used with a ratchet, not a tube socket, 5/32" worked well for me) that is small enough that the base of the turret (the part that sits flush against the top of the turret board) won't go into the hole, set the turret inside the socket, then put the board down and hammer the turret in with the staking tool. The socket ensures that the force from the hammering is applied only to the base (which is thick and not easily damaged), and the bottom (where we want the force to go in order to rivet the turret into place). Thu, 07 Aug 2014 07:48:41 -0400 Power tube low cathode voltage(by Bret Stone) Hi Everyone, Thanks again for the help on the previous issue, got me started. I took voltage readings again today, and I saw something that makes me worry. First of all here are the voltage readings that seem in line: B+ 414 B+1 412 B+2 409 B+3 294 12ax7 readings Pin 1 151 Pin 3 0.90 Pin 6 193 Pin 8 1.54 Okay now for the ones that I am having issues with: 6L6 readings Pin 3 421 Pin 4 0.1 (shows 366 in schematic) Pin 8 0.468 (shows 25.4) I checked the 1KR resistor at R7 and the 330R at R9 and they are both in range. Did I damage my power tube with my previous issue? Wed, 06 Aug 2014 04:21:50 -0400 Half power AC30 on Hoffman board(by jason d) I've got a Hoffman AC30 board and I'm thinking a 15 watt amp would suit me better. Here's what I plan on changing, please let me know if I'm missing anything. 1. Leave off 2 power tubes and associated parts 2. Use smaller power and output transformers designed for a 15 watt amp 3. Double the resistance on the cathode resistor for the power tubes. And that's about it, thanks in advance for any help.Mon, 04 Aug 2014 07:56:33 -0400 Firefly with TMB and line-out, turret strip build.(by HallwayMinstrel) Hi, Thanks to all the great info on this forum, I was able to build a firefly. It's a turret-strip point-to-point build. I'm using the ECC99 as the output tube for now, for about 2 watts. One thing I learned, make sure that R6 is as close to pin 7 as possible. I also used a NFB of 10k. The amp sounds great, and doesn't oscillate even when cranked. The headphones needed only a 100ohm resistor. It is the firezog. So, it's pretty much the Firefly schematic, then slip in the TMB stack, and add a Firezog. Here is the wiring diagram and pics on another site. I made a wiring diagram if anyone is interested (it uploaded small-ish on the other site). <a href=" " target="newwin1408687977">[link]</a> Sat, 16 Aug 2014 12:45:18 -0400 Reading Material(by Christian) Hey There, This is my first post on this forum and I heard very amazing things about the community involved with this site. I plan on building my first tube amp (Fender Champ 5f1) very soon and thought I should read up a bit on some tube amps. Which tube amp books do you reference the most? Thanks! ChristianFri, 15 Aug 2014 05:35:09 -0400 AX84 1x12 cab question(by Darren Porter) So, is the location and shape of the port critical? For example, if I wanted to do a rectangle instead of a round vent port of the same area in a different location on the back panel, would that make a difference?Sat, 02 Aug 2014 10:31:35 -0400 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=" " target="newwin1408687977">[link]</a> ). The album is here: <a href=" " target="newwin1408687977">[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.Sun, 10 Aug 2014 02:44:19 -0400 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 muchWed, 30 Jul 2014 07:16:54 -0400 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? Tue, 29 Jul 2014 10:39:22 -0400 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 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; Sun, 03 Aug 2014 04:02:52 -0400 First Power up issue with voltage(by Bret Stone) Hi Everyone, I finally finished my P1 Extreme kit, and I powered it on for the first time. Very Exciting! Well, I had it hooked into my speaker cab for a working load, and I started to see the 6L6 tube's plate turning red! I turned off the amp and started doing some diagnostics. I checked B+. the schematics show B+ to have a voltage of 388V, but mine shows 425V. In fact the B+, B+1, B+2 and B+3 all have 425V instead of dropping down like the schematics show. Is this simply a miswiring? Thanks for any help you can give. Sat, 02 Aug 2014 17:43:23 -0400