AX84 BBS New Threads as of Tue, Jul 22nd, 2014 @ 09:17:03 Amp Parts and KitsDoberman Music Products, LLC offers a variety of parts and kits Preamp with integrated graphic eq: Signal ground Vs. Virtual gro(by EeroNiemela) I''ve been tinkering with the concept of adding a graphic eq to a tube preamp (ala Mesa). The Graphic Eq schematic is this here: <a href=" " target="newwin1406035023">[link]</a> It seems to me that this is a very typical GEq design, essentially the same as eg. the EHX GEq pedal. So what I'm basically trying to accomplish is building this circuit inside the same chassis with a tube preamp. I intend to power the eq with a regulated supply off the 12,6 V tap of the PT. This supply would also power channel switching relays. What confuses me though is the grounding. The signal ground would be the usual ground lug connected to the chassis near the input jack. But what about the virtual ground of the Eq circuit? I fear that simply connecting the virtual ground to the chassis ground lug might cause a problem by making the two grounds "fight" eachother somehow. Then again, as can be seen from the schematic, the Eq circuit combines the two grounds anyway, so I can't really see a way of isolating the virtual ground from the signal ground either - the two will have to meet somewhere. So I guess my question boils down to this: Will connecting the virtual ground to the signal ground of the preamp (which is also shared by the HT (B+) filter cap grounds and safety earth connection) cause issues? Tue, 22 Jul 2014 04:04:39 -0400 FS: Epi VJ Tweed Deluxe Head Project And Nevoibe Project(by Javaman) I have the following unfinished projects for sale : 1. Epi Valve Junior Conversion Tweed Deluxe head From . This is a very Clean Build That needs debugging . It is Complete but does not power up. Comes with Tubes, Custom Face and rear plates, Power Cable, and a Beautiful Tweed Covered Epi Head Cab. If you have the ability and the time you can have a sweet Fender tweed Deluxe amp in a very small Lightweight package for the price of a pedal. $250 OBO 2. This is a completely functioning Neovibe Board that needs to be finished wiring into a brand new Pedal Parts Purple sparkle Enclosure. $100 OBO I do not have the means or time to complete these projects and need to purchase band equipment. Feel free to ask any questions PM me or email at Plenty of good deals here and on TGP Ebay ID for a reference: Jotovibe Thanks ! JT [img] <a href="[/img] " target="newwin1406035023">[link]</a> [img] <a href="[/img] " target="newwin1406035023">[link]</a> [img] <a href="[/img] " target="newwin1406035023">[link]</a> [img] <a href="[/img] " target="newwin1406035023">[link]</a> [img] <a href="[/img] " target="newwin1406035023">[link]</a> [img] <a href="[/img]" target="newwin1406035023">[link]</a> Mon, 21 Jul 2014 14:34:15 -0400 Cap coupeld reverb help(by reverberocket) Hello guys first time poster here. I have some trouble with my reverb I build in my amp. I build a reverb like a ampeg superb reverb in my tweed amp. It sounds nice but if i close the pot of the reverb it starts humming real loud. Does somebody have some ideas. I will try to get my schematic on here as soon i figur out how this works. Also thanx for all the information I already got here. I learnd a lot but I am still on a bumpy roadMon, 21 Jul 2014 15:54:49 -0400 SEL Effects Loop Noise(by DethRaid) I've added Mark Lautizer's effects loop (schematic at <a href=" " target="newwin1406035023">[link]</a> ) to the SEL I built, but I get a rather high E flat ringing out when I'm not actively playing my guitar, even when nothing is plugged in to the effects loop. My dad and I think that something in the circuit is causing my tubes to oscillate, although neither of us know why. Do any of you have any ideas about how I can get rid of this noise? Here's some more details: A few years ago, I built the SEL from the kit you used to be able to order from Doberman (no clue if you still can). A few days ago, I added in Mark Lautizer's effects loop (schematic at <a href=" " target="newwin1406035023">[link]</a> ), with the minor modification of a 2.7K and 3.9K resistor in parallel in place of the 1.5K because I forgot to order a 1.5K resistor. I attached the 4 ohm tap from my output transformer secondary to the point labelled "from Output Transformer Secondary" since I had read on this forum to just try different taps from the output transformer to see which one works the best. When I powered on my amp and flicked the standby switch, I was greeted with a very loud screeching noise, even though all my volume and gain and tone controls were set to zero. I then attached the "From Output Transformer Secondary" to ground, which results in a rather high E flat ringing out when I'm not playing my guitar. I've found that I can lower the pitch by turning up the mid knob, and get rid of the noise entirely by turning the treble know to zero, but that's no fun. I can also get rid of the noise by turning my guitar's tone knob to zero.Mon, 21 Jul 2014 07:05:33 -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="newwin1406035023">[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!Tue, 22 Jul 2014 01:37:25 -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, 22 Jul 2014 06:43:06 -0400 What should I use for the shielded wires?(by sam7arlo) First time amp build. Where do I find the shielded wire called for in this amp? Anybody know the gauge these shielded wires need to be? Thank you! Fri, 18 Jul 2014 16:29:43 -0400 Where to get parts?(by LincolnR) I'm interested in building a Hi-Octane, I've heard a few YouTube videos of people getting some cool sounds out of them and have been looking for a small amplifier that I could reasonably modify. Never built an amp before, but I've built various computer circuit boards and rebuilt various old radios, TVs, etc. so I think I could handle it. Does anyone know if Chris is still selling kits? If not, any other reasonable places to look? I know a lot of the more typical parts (jacks, resistors, caps, switches, and even most Hammond transformers and chassises) can be bought from the likes of Digi-Key and Mouser but I'm not sure about sourcing more archaic/niche stuff like tube sockets.Mon, 21 Jul 2014 08:31:59 -0400 Grid leak resistor in Single Ended amp(by Alva Goldbook) I'm working on a homebrew project, it's a class A SE amp. I'm wondering if I should use a grid leak resistor on the power tube (EL34). What makes me wonder about this is that the last pre-amp gain stage is a cathode follower, followed by a tone stack. Thoughts?Sat, 19 Jul 2014 02:07:21 -0400 Popping after startup(by Martin Bergheim) I finished the HO a couple a weeks ago. I've placed a 150k across the standby switch to lessen the strain on the power capacitors. When I power it up, B+ rises to approx 50V, then the speaker pops and it slowly falls to 20V. The tranny I use has 330V on the B+, just had to use different dropping resistors to reach the HO specs. Lately there has been intermittent popping and a scratchy noise during approx 15 after the standby is switched on, like the noise when you have no signal in old TV's. I measured that the EL84 grid drops the voltage to zero when it pops, then it comes back again. During the noisy parts the voltage just messes around from 4-6 volts (bias is 6.6V). After those 15 second everything is ok. If it is a bad cap, wouldn't it pop and scratch all the time?Mon, 14 Jul 2014 00:51:52 -0400 Really useful iPhone - Android App(by DaveW) I have come across an app called 'ElecToolKit' which I have found to be really useful and free! <a href=" " target="newwin1406035023">[link]</a> They also have 'Electronics ToolKit' which calculates LED series resistors etc. and is also free. Sun, 13 Jul 2014 13:27:52 -0400 420VCT putting out 550VCT - need ideas to drop some voltage(by Henry Ramsey) Hi all, a while ago I got a PT from ebay that was 420VCT 210-0-210@40mA. It had a label with these specs at the time which has since come off and gone missing. I've used it before in a Firefly project, but it was getting too hot so I replaced it. I think I was overloading it when the firefly was at full power. It only got hot when I played through it for a while but would cool down if I stopped playing even with HV turned on. Now, I've come back to this PT for a new low power project and in testing the HV I found a whopping 550V across and 258V from either end to the CT. I don't remember it being this much voltage and now I'm not sure what to do. I know some of that voltage will drop off, but it stills seems to say I'm going to have over 350VDC after rectification and unloaded. I ran this through Duncan's PSUDII and that's what it shows almost 360VDC under light load, but no lower than 290VDC under 40mA load. Any ideas other than to use a different PT? Could I use a FWB and only 1/2 of the HV? Could I do that with a choke input filter? I have a stancor c1001 choke here that is very hefty. It's specs are 10.5H@110mA 258R It can obviously handle the current needs of a choke input filter. The PSUDII seems to tell me I can, but in order to still drop more voltage after the choke I still need a 2.2K resistor. Thing is the PSUDII shows the inrush voltage is 166V and currnt is 75mA. After 2 seconds it goes to a more normal 70V@3mA so do I need a high wattage resistor to confront that 2 second surge or can I just just a 5W wirewound? Otherwise I'd need a whopping 25W resistor for just the inrush current. I think I actually have one so I could just use it and not worry, but it is huge. All this for a project to use 6021 subminiature tubes. Maybe I'll end up making something more normal if I cannot get the voltage down enough. What do you all think?Mon, 14 Jul 2014 13:44:36 -0400 cleaning leads on 6021 subminiature tubes(by Henry Ramsey) Hi all, last year I got four subminiature 6021s for $1 each. Here a year later and I'm thinking about a project. Three of them have insulation and were used. I need to test them out before I get a project around them going. I should be able to splice the insulation and use them normally though. The fourth one is 'new' unused and has full length, uncut leads but they're covered in black corrosion or some kind of oxidation. On resistors leads I use the jaws of my pliers to strip some of the outer layer off the lead making it shiny, but these are thin leads and doubt I can do that. What do I use to clean the leads? Fine sandpaper? Also, the data sheets say these leads are "weldable" I hope that means I can solder them too?Sat, 12 Jul 2014 16:01:27 -0400 2204 build questions(by Audiosalvage) Hi, I've posted before regarding mt 2204 build. I now have it complete and I'm confused on some issues. It sounds good at low volumes (nice and juicy 70's 80's hard rock as expected but at medium stage volumes it loses it's greasiness if you will. The headroom increases to a more bland harshness not conducive to lead playing. I've tried a few tweaks with the grid and plate resistors but the change in gain seems to go away at these higher volumes. Can you shed some light here? ThanksFri, 18 Jul 2014 16:13:09 -0400 Real Power rating of tubes(by Mark McL) HI All, Question- If you bias a tube at 70% you won't be getting the full power (Wattage rating) of a tube, correct? If so, then why are amps marketed as 100 watt amps (e.g. 4xEL34 @ 70%= maybe 17 watts x 4= 68 watts or so)?Wed, 09 Jul 2014 06:53:47 -0400 Article on effect of heater voltage on cathode current in 12ax7(by Henry Ramsey) Hey all, I have been absent from AX84 for a while now. I miss tube amp building and hope to build something again soon. I got a bunch of 6021s for $1 each about a year ago and have yet to test or try them out. I found a 125V and 6.3V transformer in my collection which might just power them. I need to figure if the 125V part can supply enough current for a 5902 power amp sub mini tube or if I need to get a different PT. I also need to get the aforementioned tube as well but they're only $10 on eBay shipped so that is easy. Anyway, while looking at Adam Alpern's old site for info on sub-mini tubes I came across a project from 2001 at U of Illinois to make a sub miniature Fender Princeton. I will probably use that for my project since I have never built a Fender based project before. Also at that page I found this which may or may not have been posted here before: <a href=" " target="newwin1406035023">[link]</a> This is indeed an old article, but given it's subject I thought it might be interesting to post it here.Mon, 07 Jul 2014 20:33:03 -0400 Totally Tubular (dudes)(by Douche Baggins) This link <a href=" " target="newwin1406035023">[link]</a> has probably been posted here before. It's a good reference for tubes and power supplies.Tue, 15 Jul 2014 16:05:16 -0400 Deluxe Reverb from Wurlitzer organ amplifier(by zombiestomp) I obtained a free working Wurlitzer organ, model 44__, which appears to be from the late 60s. It works, but is quiet. The power tubes are marked as 7027, but have been replaced with 6L6s. The preamp has 4 12au7s and one ____. This model had a motor powered tone generator box, so does not have a bunch of little preamp tione generation tubes. What I don't see on the amp is an output transformer, so either I'll have to continue dismantling to find it, or obtain one somehow once I find out what I need to get. I also do not see a choke transformer, but I don't yet understand how they work within the amplifier circuit, so I'll have to cross that bridge when I get to it. The preamp tubes section basically takes place on a primitive circuit board, so I ordered 6 nine pin sockets I can rivet in instead as well as some classic fender style knobs. My intention is to build something that is in the power range of a Fender Deluxe Reverb, with a fender reverb unit grafted onto that. That part is at least available in it's own kit, which I may or may not have to buy to be able to build. If it's worth the $150 or so bucks, I may get that and add it on, depending on how much I'm able to learn building the basic amp. I'm not too hung up on making a blackface deluxe reverb clone, something that sounds generic, primitive, and loud like a Silvertone head might actually be preferable. I just want to have a louder amp for a reasonable price, with a fender reverb unit to get that reverb sound, and be able to try out the dwell feature that the reverb unit has that I've never been able to try out. First I'm going to try to find the output transformer. Then I'm going to try to get something patched together where I might try playing guitar through that with the original speaker still mounted in the organ. If feasible, I may try adding tone controls to that existing design and recapping it. If it is determined that this setup might not be much louder than my 15 watt ampeg jet 2, I will try to find a schematic/ layout for another circuit design that mimics the Silvertone or Fender Deluxe, and add the fender reverb unit, provided I have the right ingredients. If I don't , I'll have to find a way to just simplify the existing circuit, rebuild all the parts, and add myself a reverb unit. Suggestions starting out? I have rebuilt a few tube amplifiers, but this will be the first build. I've been studying tube amplification in my spare time, so pointers to learning material that might help me enough to work into this long-term advanced build are also appreciated. Fri, 04 Jul 2014 18:06:52 -0400 First amp issues(by MartinG) I just finished building a P1-eXtreme. The sound is nice, but it doesnít seem to clean up as well as I would like and it doesnít seem to get as dirty as the samples that I listened to on the internet. With the preamp volume as low as I can get it, I still hear some distortion. Iíve checked the components and wiring and am not opposed to checking again. Meanwhile, Iíve noticed two things. My B+3 voltage is 260 volts (as opposed to 274) and the plate voltage V4B is only 156 volts (as opposed to 181). The grid voltage on the first preamp is 1.49. Iím new to the mysterious world of analog circuitry and am not sure if this low plate voltage could be problem. The second thing that might be an issue was my choice of capacitors for C14 and C7. Both of them appear to be cheap ceramics. Can they be causing distortion? Any help and/or suggestions are welcome. Thanks.Mon, 07 Jul 2014 21:11:57 -0400 Uber sel power supply(by Scrounger) I have been looking at the Uber sel power supply and wondering if it could be made output voltage adjustable. I was thing of taking the 470k oh resistor on the bul-390 and tying that to a wiper on a 1 meg pot with ends tied to the supply and to ground. Like what they did here: <a href=" " target="newwin1406035023">[link]</a> The reason I want to do that is I have a bunch of power transformers that are slightly higher voltage and I would like to be able to vary the output voltage to fit this amp. I like that fact that these are very low ripple supplies and I think I could use this for other things as well.Sun, 06 Jul 2014 18:21:22 -0400 Pics of using zip cord for heaters?(by Darren Porter) Anyone have any gut-shots of using zip cord for their heater runs? My Google-fu isn't coming up with anything and I know from posts I've read here that people are doing it. Just want to see how you are running the wires and laying them out in the chassis. I'm thinking I might re-wire my push-pull reverb unit using zip cord. I have to admit, running those twisted heater wires and getting them to look all neat and proper is my least favorite part of a build. I am hoping zip cord will ease that pain ;-)Fri, 04 Jul 2014 12:10:16 -0400 Finished my simple/20wPP build...(by Darren Porter) After waiting three weeks for my Edcor iron and finalizing exactly what I wanted to do with this build, I sort-of finished my Simple-Preamp/20W Push-Pull build late last night. I couldn't really put it through its paces until this morning, and wow am I pleased with this amp! The amp has more headroom than I expected. With the MV all the way up, there is no preamp breakup until I get around halfway on the gain knob. Full-on gain (with the dual-humbucker active guitar I was using anyway) was a little much but there are plenty of very useful spots on the dial. Lots of pleasing punch and very nice compression without being over-the-top so I think the decision to go with the simpler diode rectification over tube was the right one. The tone stack works great, giving me a lot of flexibility and dialing-in useful tones is easy. The bass knob works really well to tame the low-end when the gain and volume are getting pushed hard. I find the presence control to be very musical letting me go from a tad too "sparklie" to a bit too dark pretty easily. It is pretty loud running through my 2x12 Celestion V20 cabinet! Thank goodness the master volume works pretty well! I have a VRM module (power scaling) that I purchased for a kit I bought from Trinity Amps but I did not install it in the Trinity since it is only 15 watts. I might put it in this one, but the MV does work pretty well so I may not go through the trouble. I am somewhat surprised by how much louder this amp is than my Trinity 15-watter. I wanted to get the amp working right before I added anything else so it is currently just the pre and power amps. I had one issue with my fix of the layout error on the Simple-Preamp layout here. My fix was correct, I just had one of my anodes going to the wrong turret on the board. My next step is to install Merlin's effects loop from his 2nd-edition book (thanks for your help sorting this out Merlin) and then I might install a reverb circuit. I have all the parts and the chassis is drilled for them the sockets are installed, I just need to get it all wired-up. There were a few people here who helped me get this sorted out. Thanks to all of you for answering my questions so well! I'll get pics up on my blog soon...Mon, 07 Jul 2014 17:07:06 -0400 Getting jimmy page tones out of P1?(by mike64b) Hey this is probably a dumb question but I built a P1 a few months ago and I really like it but I can't quite seem to get a tone like jimmy pages solo playing (specifically stairway to heaven solo). I'm not good at describing what the tone difference is but it just doesn't sound the same. I'm using a strat with a HSS config and playing with the humbucker. I also have a MXR classic fuzz 108 and a BOSS DS-1 pedal that I use which makes it closer but something is still off. Again, probably a dumb question but is there some magic mods I can do to achieve jimmy page tones? Thanks!Sat, 05 Jul 2014 13:59:34 -0400 What is the diff between these input stages(by BSharp) <a href=" " target="newwin1406035023">[link]</a> Link above of schematic pertaining to questions. I wanted to start fresh with these basic questions and follow on with new ones in the future as I sort out my basic theory. I built the more complicated version of the first triode stage, (B.) in a clean preamp and ran into problems with oscillations and perhaps feed back. The end result was the simplifying of the circuit to version (A.). Version A, works and perhaps since the first version B, was laid out on terminal strips and UN-shielded that was the cause of the problems. The original layout in the Peavey did have a section of copper clad board over top the preamp stages and the layout was PCB based, (circuit B). The circuit B, was used as the 1st stage feed, either the Clean chan. or the High Gain chan. depending on selection. (most likely the High Gain required additional filtering, I don't know). What was the advantage of the more complicated version, circuit B?Sat, 05 Jul 2014 22:22:15 -0400 Capacitor voltage advice(by DaveW) I am building a headphone amp (as my kids protest at my taste in music) and have started to build this. <a href=" " target="newwin1406035023">[link]</a> I am using recycled parts and a chassis I already had lying around. However I just can't fit the 470uf 350v - C4 used in the optimised circuit (fig. 4 - which is strangely after fig. 5?) caps into the space I have. The original circuit (fig. 1) used 220uf 350v and a Chinese clone I found uses 470uf 200v in this position. The voltage across this cap seems to be about 111v and I can't see a fault condition (that is reasonable to assume) that would result in much more than this. What is the lowest working voltage I could use while still remaining within safe margins. Any advice gratefully received. ThanksSat, 05 Jul 2014 08:15:15 -0400