AX84 BBS Threads with new messages as of Fri, Aug 22nd, 2014 @ 05:30:09 Amp Parts and KitsDoberman Music Products, LLC offers a variety of parts and kits how loud p1 should be?(by Supakas) Hell7 Just finished my first tube amp build. I choosed p1. Everything went smooth. Amp is working .. no hums or buzzez. But one little question. How loud this should be? Right now i have tryed with 1x12 16ohm ibanez speaker what is rated over 200 watts. And this is not in cab.... so it feels little quiet... Is it because the speakeris not in the box? The sound is realy nice and clean but just feels low. Is 4ohm speaker louder than 16ohm?? I have lc30 combo with 4ohm speaker where i can try but just wanted to ask first. Anyways thanks for the nice documentation . It was realy good to build this, and sorry for my english. Best wishes from Estonia. KalmThu, 21 Aug 2014 22:29:50 -0400 Hybrid 1 Watter (not mine)(by Douche Baggins) Did a YouTube search recently for 1 watt amps and this: <a href=" " target="newwin1408699810">[link]</a> is among many posted. Here: <a href=" " target="newwin1408699810">[link]</a> is the schematic/build link. Build pics: <a href=" " target="newwin1408699810">[link]</a> Cheers to nzCdog for the build, video and guitar chops.Thu, 21 Aug 2014 21:29:39 -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 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 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 Help! How is this possible?!?(by tooltime) <a href=" " target="newwin1408699810">[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 Resistor in series with cathode bypass capacitor(by Yeto) What effect does placing a resistor in series with a cathode bypass capacitor have on the sound and electronic values of a circuit?Wed, 20 Aug 2014 07:36:59 -0400 Soldering to turrets(by David Staepelaere) Here's an old instructional video on soldering to turrets... <a href=" " target="newwin1408699810">[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 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 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="newwin1408699810">[link]</a> <a href=" " target="newwin1408699810">[link]</a> When my daughter in law saw it she asked if I could make a letter opener for her so . . . <a href=" " target="newwin1408699810">[link]</a> <a href=" " target="newwin1408699810">[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 Inexpensive P1 type amp kit, any interest?(by Matt Burns) Hi, I run a small business selling electronic kits for radio related projects and am thinking about offering a low cost tube guitar amp kit, maybe something along the lines of a P1 or HO. The kit will include a printed circuit board, all on board parts (probably poly film capacitors of Chinese origin), pots for gain/tone controls (will not be board mounted), chassis mount tube sockets, NOS Russian tubes, probably a 6n2p (dual Hi-Mu triode with 6v heater) or two and a 6p6s (Russia's clone of the 6v6), a "70 volt" PA line transformer for the output transformer (still need to test this, the 0.625 watt tap should be about 7900 ohms but the 30ma+ DC may put the core near saturation). A power transformer will not be included but I will suggest using two radio shack power transformers (one reverse wired to provide a line isolated HV supply feeding a voltage doubler to give ~300vdc under load). I may also offer a predrilled cake pan chassis or possibly a wooden chassis backed with some sort of aluminum flashing material. Would there be any interest in this sort of kit? I haven't ran the numbers on it yet but I think I will be able to offer it for around $50. Matt Burns Cycle 24 KitsTue, 19 Aug 2014 15:03:34 -0400 Univox U-45(b)(by Ken Graves) I just found this video: <a href=" " target="newwin1408699810">[link]</a> That's the first amp I ever owned. I thought it sounded pretty good then and this video makes me think I was right. So I'm considering building one. I found a schematic (attached) but, though it doesn't show the HT, it does show the PT secondary at 250-250 at 50 mA. I'm unfamiliar with 6BM8 tubes but I'd bet I could get NOS examples for cheap. The 12AX7 is only used for the tremolo! And the 6X4 is common enough, I think. I even found a modded schematic that allegedly gets it closer to the Gibson it's supposed to be patterned after. There's a U-45 and a U-45b. I don't know the difference - some say the 45 is single ended and the 45b is p/p. The schematic here <a href=" " target="newwin1408699810">[link]</a> is the 45b. The one in the video looks just like the one I got when I was 15 (got it used - a year old) so I'm thinking that mine was the 45b. Anyway, just wondering if anybody has any experience, info or thoughts about these.Tue, 19 Aug 2014 10:21:53 -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="newwin1408699810">[link]</a> Thanks guys!Tue, 19 Aug 2014 05:52:03 -0400 working fx loop(by jonm) hi have been trying to build a effect loop into my hi octane without much sucess untill i used this <a href=" " target="newwin1408699810">[link]</a> i have guitar rig 3 ( i know its software dont shoot me down) i can now go effects send into sound card ,return back into amp can have delays,reverbs,flangers ,chorus ,any rig effect through my high octane, and play backing tracks . amp still has its distortion . used a 12ax7 for the return i have a el34 output tube in the amp. i am for the moment happySun, 17 Aug 2014 06:43:56 -0400 Graphic EQ slide pot value(by EeroNiemela) Hi, I have been looking into this GGG Schematic for a 5-6 band graphic EQ. Schematic here: <a href=" " target="newwin1408699810">[link]</a> The project calls for 5k linear pots, and I'd really like to use slide pots for this one. However I can only easily find 10k or 100 k slide pots. Is the value of the pot critical in this circuit? I have no deep understanding of the curcuit or how it works, but it seems to me that the slider only works as a voltage divider between boost/cut, so the value will not be critical and even 100k pots will do fine. Am I correct? Would I need to change the values of some of the resistors in the circuit to make the 100s work well? Thanks!Sun, 17 Aug 2014 00:25:05 -0400 Salvaging TV guts(by MRHIGHSPEED) I'm knew to this. Thinking it'd be cool to build a tube amp with my teenage boys. Not to mention, to have a tube amp. We've got a couple of CRT TVs, circa 1999, in the garage. Any thoughts on whether they might contain anything worth salvaging?Sat, 16 Aug 2014 14:58:23 -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="newwin1408699810">[link]</a> Sat, 16 Aug 2014 12:45:18 -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="newwin1408699810">[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 440 pre + 20W push pull PA(by JHoff) Hi All, I noticed that the simple preamp is about four components shy of the 4-4-0 preamp. Would the 4-4-0's preamp conceivably work well with the 20 W Push Pull amp. I have a simple preamp with a 20 W Push Pull power amp, and the conversion looks very simple. Any thing I need to be cautious of in adjusting component values, etc., or would it be "plug and play"? Thanks!Fri, 15 Aug 2014 14:23:51 -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 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="newwin1408699810">[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 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 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 wall voltage too high = high heater voltage?(by bustapr) hello, I am building an amplifier as a college project/assignment to demonstrate next semester for the future freshmen. Ive taken schematic of the x88r preamp and made a few mods to it, added the 50w pp poweramp from ax84, and a few other things to make it unique enough to not feel like I ripped off the schematic entirely. the thing will 6 12ax7s and 2 el34s. the heater current draw should be around 5A(the PT I plan on using has more than enough). the problem is that the voltage in my apartment varies from 125v-128v from month to month. this would make the heater voltage 6.56-6.72V at my house. the voltage at my college is a solid 120V. my questions are, is this heater voltage Id get at my house safe for the tubes? if I were to cut the voltage with resistors, what ohmeage would be good? is a low heater voltage safe(like 6V)? will these resistors add too much noise(its a dc elevated heater design)? does dc heater elevation have a significant impact on tube life? i read on another forum that using shotkey diodes is the best way to cut the heater voltage, is this true? sorry for all these questions, just some things Id like to clear up before finalizing the design.any answers would be greatly appreciated.Tue, 12 Aug 2014 05:43:10 -0400 Two 12AX7 Two Channel(by Lil Bagu) Working on a two tube, two channel amp and trying to find the best way to isolate the signal between the two tubes. Purpose is to have two completely independent channels with two gains and two master volumes. See Link: <a href=" " target="newwin1408699810">[link]</a> Anyone see any issues with running just pins 2 and 7 as a quasi parallel input while seperating the cathode and anode into two seperate signals. I have also added 1M resistors around the relay to reduce popping during channel switching. Any help is always appreciated.Mon, 11 Aug 2014 10:13:07 -0400