AX84 BBS New Threads as of Wed, Jul 30th, 2014 @ 11:37:33 Amp Parts and KitsDoberman Music Products, LLC offers a variety of parts and kits 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="newwin1406734654">[link]</a> ). The album is here: <a href=" " target="newwin1406734654">[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.Tue, 29 Jul 2014 07:56:34 -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; Tue, 29 Jul 2014 06:10:25 -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. Tue, 29 Jul 2014 05:59:28 -0400 Knowledge is Power - pun intended 'cause I think I'm funny(by BC Walter) I've been interested in electricity and electronics - specifically tube amps and circuits since I was a pup. I'm mechanically inclined and have mastered all the hands-on aspects of amp building. I'm pretty well versed in the functions of each component. I can identify different types of circuits and follow a signal path on a schematic. My troubleshooting skills are tolerable: meaning I can identify WHERE a problem is or might be. But when it comes to actual to circuits I'm still in that state of not quite understanding why things are connected as they are and what effect(s) different component values have on the circuit as a whole. Having said that, I am constantly searching for texts/references that I can actually understand! If you're just starting out, or are like me with some skills but still not "getting it" and want to - I've found the following useful: <a href=" " target="newwin1406734654">[link]</a> <a href="*&destination=us&currency=USD&binding=*&isbn=0-89512-034-8&keywords=&minprice=&maxprice=&min_year=&max_year=&mode=advanced&st=sr&ac=qr" target="newwin1406734654">[link]</a> Mon, 28 Jul 2014 08:56:18 -0400 Square wave testing for freq. response.(by Dan Moos) Okay, so I know I can inject a square wave into the input of a gain stage and test the freq response by observing the way the wave is altered. Is it true that I should be able to inject a square wave of a specific frequency, and get a rough idea of the specific frequency response by noting where specifically the square starts to drop off? In short, is a square wave and a scope all I need to get some actual rough numbers? I feel like this should be the case, and that the math should even be pretty simple. My intuition says that if I measure the time from the wave's start, to where it flattens at full strength, that would be the high response, and if I measure the start, to where it again begins to drop off from flat, that would be the low end. First, is that right, and second, what is there a proper way to select the frequency of the injected square wave. I imagine that I would use a lower freq square to test bass response, and vice versa so that the time division on the scope can be set for a nice big wave that is easy to interperet. Can I do this? I realize I can sweep the freqs and note the point of drop off, but I want to know if this method also is viable. As a related side note, if I want to test each gain stage individually, is there any reason I can't put the signal at each grid without disconnecting the previous stage? I'm having trouble visualizing whether this will give me an accurate frequency response test, because I'm not sure how the previous stage looks to the signal impedancewise when I inject a signal this way. Fri, 25 Jul 2014 23:31:00 -0400 the man who played the first jazz guitar?(by Kursad K) <a href=" " target="newwin1406734654">[link]</a> <a href=" " target="newwin1406734654">[link]</a> Kursad Wed, 23 Jul 2014 12:21:12 -0400 TAG?(by PhilS) I know there are several cross posters between AX84 and The Amp Garage. TAG seems down for the count. Anyone know anything? --Sign me Worried.Wed, 23 Jul 2014 16:41:04 -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, 26 Jul 2014 10:13:24 -0400 Stoking the boiler for a new build(by ve3vxo) Hello to the list, this is my first post here. AX84 is a great site and many thanks to all the contributors. I have never built a tube amp before but I have extensive experience with industrial electronics, HV, have built a few amateur radio transceivers and lots of other stuff, so although I was warned to build the P1 as a first amp I am unwisely going to ignore that and build the amp I really want which is the 4-4-0. I'm not likely to build many amps so I am going for the type of amp with the character I really desire. I have troubleshooting tools and skills. Hopefully it won't be a bad choice on this. I've been doing some reading here, on amp garage and music electronics as well as websites like Aiken, Ruby and others to bone up on tube circuits. I have some preliminary questions for the graybeards on this list. 1. There seems to be quite a bit of discussion around the PI and finals section of the design regarding balance, matching of the drive dynamics between the input needs of the PP section and the output characteristics of the PI. Specifically I have read a lot about the Chuck H. mod adding a zener clamp on the cathode resistor of the PA and then the Ruby mod with the zener clamping of the grids. I noticed these changes have not been added to the latest schematic but should I plan on having them? If I understood Tilly Dog correctly, although a 12AX7 has higher voltage gain it doesn't have the power gain necessary to overdrive (as badly) the PA like the 12AY7 can but since the schematic still calls for a 12AY7 was this just an isolated case in Tilly Dog's build or is this something many people have changed? 2. I found another website from someone who recommended a different OT than the hammond which has higher primary inductance and it made sense to me to order one for the build. Also it has shielding which will take a paint job and look nicer than the open frame hammond. Are there any other component substitutions that I should consider as a good idea before I order more parts? JoeSun, 27 Jul 2014 16:05:39 -0400 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="newwin1406734654">[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="newwin1406734654">[link]</a> [img] <a href="[/img] " target="newwin1406734654">[link]</a> [img] <a href="[/img] " target="newwin1406734654">[link]</a> [img] <a href="[/img] " target="newwin1406734654">[link]</a> [img] <a href="[/img] " target="newwin1406734654">[link]</a> [img] <a href="[/img]" target="newwin1406734654">[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 roadThu, 24 Jul 2014 13:05:49 -0400 SEL Effects Loop Noise(by DethRaid) I've added Mark Lautizer's effects loop (schematic at <a href=" " target="newwin1406734654">[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="newwin1406734654">[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.Sun, 27 Jul 2014 11:19:32 -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="newwin1406734654">[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 KitsWed, 23 Jul 2014 22:54:12 -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! Thu, 24 Jul 2014 07:13:34 -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.Sat, 26 Jul 2014 20:12:35 -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="newwin1406734654">[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