AX84 BBS Threads with new messages as of Tue, Jul 22nd, 2014 @ 19:17:52 Amp Parts and KitsDoberman Music Products, LLC offers a variety of parts and kits 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 19:07:43 -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 roadTue, 22 Jul 2014 11:27:57 -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="newwin1406071073">[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 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="newwin1406071073">[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 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="newwin1406071073">[link]</a> [img] <a href="[/img] " target="newwin1406071073">[link]</a> [img] <a href="[/img] " target="newwin1406071073">[link]</a> [img] <a href="[/img] " target="newwin1406071073">[link]</a> [img] <a href="[/img] " target="newwin1406071073">[link]</a> [img] <a href="[/img]" target="newwin1406071073">[link]</a> Mon, 21 Jul 2014 14:34:15 -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 SEL Effects Loop Noise(by DethRaid) I've added Mark Lautizer's effects loop (schematic at <a href=" " target="newwin1406071073">[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="newwin1406071073">[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 Vibrato/Phasor design using Nuvistor tubes(by CChurchill) This is my first post and I want to say that the community of members here are like heros to me. I have learned so much from the people who share thier ideas, experience, and knowledge on this forum. I'm still learning.... So, I scored a few different kinds of Nuvistors from an old Tektronix Oscilloscope(at first glance I thought they were some kind of power resistor or something). The small size and (relatively)low plate voltage they are designed for have me thinking they would be great in a stompbox or effects build. I have one 6CW4(high mu), two 7895(high mu), and four 7586(medium mu) nuvistor tubes. There isn't much in the way of good information on these out there other than the data sheets I have with the anode and grid characteristics. But its a good place to start. I'd like to see if these might be a good fit for a Vibe/phasor circuit. Maybe design an analog of Merlins Vibrotron using these. I've see nuvistors come up for discussion from time to time. So, if anyone else has any of these lying around and wants in, or has any interest in this project, I'd be interested to hear your thoughts.Sat, 19 Jul 2014 22:58:47 -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 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 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 2204 build problem(by Audiosalvage) Hi, I'm finishing a marshall 2204 amp and something is not right. i get a slight hum when switched on but only works through the return loop. Also the choke is getting very warm. How should I go about troubleshooting this?Fri, 18 Jul 2014 13:12:35 -0400 single coil pickup spice model?(by David Staepelaere) I'd like to play with simulating the effects of guitar volume/tone knob settings. Can anyone point me to a reasonable spice model for a guitar pickup and cable? Single coil parameter values would be preferable, but I don't suppose it will really matter that much for what I'm doing. Thanks!Fri, 18 Jul 2014 02:55:35 -0400 p-p 6v6 Hi-Octane(by Matt Burns) Hi All, here are some pics of a push-pull 6v6 Hi-Octane I'm building for a friend. <a href=" " target="newwin1406071073">[link]</a> I'm using a cakepan for a chassis and actual point to point wiring (no turret board). I plan to add two solid state preamps, one feeding into the first tube preamp stage for sort of a heavy metal sound and one that bypasses the tube preamp completely and feeds directly into the phase inverter for a clean sound. The preamp selection will be controlled by a momentary tattoo machine style foot switch, through a debouncing circuit, into a 74hc4017 counter that will cycle through four different preamp settings using a cd4066 quad analog switch IC. The settings are tentatively 1-solid state clean 2-tube clean(bypassing the first tube preamp stage) 3-tube overdrive(straight into the normal first tube preamp input) and 4- evil screaming b@stard (solid state preamp feeding into the first tube preamp stage). In my head this sounds awesome but we shall see if that holds true once it is completed. As of now the amp sounds awesome as a pretty much stock HO and the 6v6 PA is doing somewhere in the area of 5-7 watts with 230vdc on the plates of the Russian 6p6s tubes. It's still a work in progress so the wires going to the power supply are a rat's nest and will be straightened up and connected with molex connectors as time allows. Also, note the green micamold tropicaps in the first pic and that they are replaced by Sprague "orange drops" in the later pics....the tropicaps were leaky in a bad way. Matt P.S. Anybody need some leaky green capacitors? I have loads of them!Wed, 16 Jul 2014 10:46:30 -0400 Class A and AB amplifers(by GeoMan) My guitar instructor recently became the owner of the studio he teaches at. He's going to try to run a custom guitar shop out of it as well and asked me if I'd be interested in putting a couple of amplifiers in it to sell. We got to talking about the kinds of things he'd like to see in an amplifier and he brought up something he thought he'd seen where a switch could be used to switch between a Class A output and a Class AB output. I've been under the impression that Class A was single ended, and Class B and AB were push-pull amps, and that's how it has to be. I've done some google searching, and according to everything I've seen, that sounds right. However, he's a smart guy, and my knowledge is far from infallible, so if someone can set me straight, I'd appreciate it. Thanks PLWed, 16 Jul 2014 03:42:44 -0400 Totally Tubular (dudes)(by Douche Baggins) This link <a href=" " target="newwin1406071073">[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 Modified Layout(by Rick West Coast) This is my first post. Just finished a 5F1 type amp as my first project & now planning my next build. I've got the cabinet to a 1930's radio and want to fit a guitar amp inside. The largest chassis that will fit is 11x7x2, it only has holes for 2 controls and the input jack based on a P1 design. Looking for one volume, one tone control. Speaker will be a Weber 6" so will opt for the 6N1P output Thanks in advance for any suggestionsTue, 15 Jul 2014 09:24:17 -0400 Merlin's U-boat sub octave question(by Stevo) So, I recently put together Merlin's sub-octave effect - <a href=" " target="newwin1406071073">[link]</a> - and it works, but not perfectly. The issue I seem to be having is the effect does not seem to be tracking very well. The output sounds distorted, not very smooth, and the tracking tends to jump around a lot. Anyone able to offer some insight? Where should I look?Tue, 15 Jul 2014 07:19:51 -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 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 What brand EL34's do YOU like?(by Craig W) Hey guys, I've not really dealt much with EL34's so I'm interested in getting a feel for some of your impressions. I'm currently building a SE amp designed for an EL34. What brands do you guys like and why? Thanks!Sun, 13 Jul 2014 17:32:03 -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="newwin1406071073">[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 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 100+ Watt Power amp(by Gruszie) Just wanted to share another project that I just finished up. The is a 100+ watt El34 power amp that I build for my Rhythm Guitar player. Like many others, he uses an effects processor for all his tones and then he would run the signal to the input of his clean channel of his head. After trying to explain to him that running his signal that way is not the best way of doing things I decided to build him this amp and let him hear the difference. I added a Presence and Resonance to help with some tone control and that's about it. Tube CAD calculated the output power at around 117 Watts +4db input level. Output Tranny is out of a Peavey jSX Head and all other tranny's are new. Not too difficult to design. and this thing is almost dead quiet at idle. A fun build and hopefully my guitar player will like it and pay me big bucks for it LOL. Thanks for looking. <a href=" " target="newwin1406071073">[link]</a> <a href=" " target="newwin1406071073">[link]</a> <a href=" " target="newwin1406071073">[link]</a> <a href="" target="newwin1406071073">[link]</a> Sat, 12 Jul 2014 09:15:47 -0400 First Build: Blown Cap!(by brandoncarlisle) "Finished" my firefly PCB, mounted to the enclosure, wired all off-board components (but haven't soldered them yet). There was one thing I wasn't certain of: In the PCB guide, it looks like the ground and negative terminal of the 1/4" output jack are jumpered together. Is that right? I hooked it up to a WGS Veteran 30 and fired it up: light on, tubes glowing, very low hum--even at high volume. I plugged in my guitar and switched the standby and it played fine for about 30 seconds. Then there was a popping sound, sound output stopped abruptly save for a now loud hum, and my C9 capacitor started smoking. Is it just a bad capacitor? Or will replacing it just blow a new one? There's a chance that one of my unsoldered connections slipped (particularly the AC connector ground to the enclosure). Any ideas are helpful. Thanks!Fri, 11 Jul 2014 18:13:44 -0400