AX84 BBS New Threads as of Fri, Dec 19th, 2014 @ 06:31:50 http://ax84.com Amp Parts and KitsDoberman Music Products, LLC offers a variety of parts and kitshttp://shop.dobermanamps.com OT placement/wiring (by Denny Gracey) The only residual issue from the SEL build was OT hum, so decided to pull the board and do the headphone trick. Ironically the original placement (right next to PT per the standard board layout) turned out to be the worst, but unfortunately the quiet spot is directly over the pre-amp circuit. Looking for advice to minimize hum induced by secondaries. Couple initial questions: * The OT is equally quiet with 180deg rotation, so I can drop the secondaries thru the hole over gain 1 circuit, or over the tone stack. Suggestions? * I found on the forum recommendation to twist the secondaries but not clear on how to do that since I've got 4 wires (4/8/16 plus ground). Ideas, links, advice appreciated!Fri, 19 Dec 2014 04:03:14 -0500 http://ax84.com/bbs/dm.php?id=487939 HIgh voltage supply with mosfet regulation(by DanGu) Hi. I've got two power transformers rated 720VCT @ 260mA which I'd like to use for a bench high voltage supply to use for amp testing. I'm bored to build always the power supply searching for random transformers here and there or adapting them back to back or similar. So this has to be regulated with HT mosfet, and I'd like to select the voltage with a pot from 0V to about 480V. For the circuit I'd like the following approach <a href="http://www.eleccircuit.com/wp-content/uploads/2012/07/the-variable-high-voltage-power-supply-0-300V.jpg " target="newwin1418988711">[link]</a> Only needs to change the mosfet for higher voltage and sense resistor for current limiting The other thing I would change is the pot. It would have about 450/500V across it, and I think it's a bit dangerous if it fails. How can I regulate the voltage in a safer way? Do you know of any good 600V mosfet? Fri, 19 Dec 2014 03:13:26 -0500 http://ax84.com/bbs/dm.php?id=487906 .25 (1/4) watt Project(by Jazz5dad) Request a little help here, may have been addressed somewhere but donít see where. I want to design and build a .25 watt tube amp with volume and master only without sacrificing tone. I already built the Gilmore Jr and the tone is fantastic. Iím thinking about using design of the Gilmore Jr as a base to modify but not educated enough yet to make those changes without some guidance. Also, if there is a prof tested design on this, or any other forum, already in existence with similar design, I would like to take a look and study. Your help would be greatly appreciated. Thanks Ken Wed, 17 Dec 2014 14:32:02 -0500 http://ax84.com/bbs/dm.php?id=487889 Wanted: fuses 400+ V(by Henrik Lidbjrk) I want a fuse for the B+ line (after rectifier) in my 6V6 Plexi build, but can only find fuses rated 250V. I need circa 400 V. Maybe 500 V is the next step after 250? Preferably 250-500 mA or thereabout. The usual small size glass fuse for mounting in a clamp style fuse holder inside the chassis.Thu, 18 Dec 2014 05:13:16 -0500 http://ax84.com/bbs/dm.php?id=487888 Where to solder the 50V bias wire?(by Henrik Lidbjrk) I'm building a Mark Huss 6V6 Plexi, and in his schematic there is no separate bias wire from the OT, so he connects one of the HT secondaries to the bias circuit through a 220k&#937; 3W resistor. My OT has a dedicated 50V bias wire and I thought it would be neat to use it. So, do I simply connect this bias wire directly to the diode in the bias circuit and skip the 220k&#937; resistor?Tue, 16 Dec 2014 03:07:37 -0500 http://ax84.com/bbs/dm.php?id=487881 Soft-start (standby) switch -- before or after rectifier?(by Henrik Lidbjrk) I'm about to solder a "soft start" switch, as Merlin has outlined on his Valve Wizard site ( <a href="http://www.valvewizard.co.uk/standby.html). " target="newwin1418988711">[link]</a> This is in place of a standby switch and has (in my case) a 68 k resistor across the switch. But I'm not sure if I should put this switch before or after the rectifier? In Merlin's example, he's putting the switch after the rectifier, but on the same page he writes "A switch will lead a happier life in an AC circuit rather than a DC circuit [...] putting the switch before the rectifier is to be preferred." Maybe the AC/DC factor doesn't matter with the soft start switch design? My build is a 6v6 Plexi by Mark Huss: <a href="http://www.mhuss.com/Plexi6V6/Plexi6V6c.gif" target="newwin1418988711">[link]</a> Fri, 19 Dec 2014 03:34:51 -0500 http://ax84.com/bbs/dm.php?id=487880 FMV tonestack "sweep" idea.(by Greg Robinson) Hi everyone, I got to thinking about sweepable mids on a FMV tonestack recently, I often get requests for this and have always done the "shift" type control, adding a pot in series with the slope resistor, as is quite popular. It works, but I've always wanted something that behaves a little differently, isn't quite as lossy, and works a little more intuitively and controllably with commonly available pots (I never liked the "backwards" behaviour of an audio pot for the shift control, and using a linear lost all fine control). So I just did a quick simulation of an idea, I'm sure it's not original, but I don't believe I've seen it anywhere else, so I thought I'd share. I haven't actually tried it yet, so it's worth as much as you've paid for it right now ;) It simulates as working equally well plate driven, although in this example I've used typical cathode follower source impedance, and Marshall style component values. If you were to try this with Fender style values, you'd probably want to up the "sweep" pot to a 250k or thereabouts. Let me know if you've seen this idea before (and where) and what you think, and especially if you've tried it before. I'll give it a try as soon as I get a chance. <a href="https://www.dropbox.com/s/g7sbqvbdx6aiszh/Tone%20stack.jpg?dl=0" target="newwin1418988711">[link]</a> Sun, 14 Dec 2014 23:53:08 -0500 http://ax84.com/bbs/dm.php?id=487868 Gearing up for October build (finally)(by Darren Porter) OK so I've had my eye on the October for a long time and I'm going to go ahead and take the plunge. 1) After reading every thread about the October in this section, I have come to the conclusion that I should build the Birthday Club 10.10.10 preamp. There should be no issues connecting this to the Stage MV and power amp section, right? I'll go ahead and install the switching option too. 2) Just how loud is the Club 6V6 version? Will it be just as loud or louder than my 20W push-pull core that I built? I will be playing with a band and the other guitar player has a JTM45 clone so I will need to keep up with him and the drummer. Which is why I am thinking the Stage version with VVR/Power Scaling might be best for me so I can have a little more clean headroom. 3) I'd like to do an effects loop. Anyone have much experience with O'Connor's loop in his TUT series? Or Merlin's from his preamp book? I'd like it to be as transparent as possible. Or should I just go SS since all the effects in the loop will be SS too? I am thinking Hammond iron for the PT and the Choke with the Heyboer OT if I do the stage version. Sun, 14 Dec 2014 22:01:08 -0500 http://ax84.com/bbs/dm.php?id=487867 Daisycutter Voicing(by mjones32) Hi,new boy here, looking for some advice on how to go about 'voicing' an amp. I built a variant of the Daisycutter using 6AQ5A output tubes, but otherwise sticking pretty much with the published schematic. It sounds pretty good, low hum, more than loud enough to jam with a drummer and has really nice range of gain options. I'm just a little disappointed with the amount of tonal variation from the tone stack and its just a little darker than I would like. So I would really appreciate any suggestions about how to even approach fine tuning the voice of an amp. Where should one start ? Sun, 14 Dec 2014 14:50:02 -0500 http://ax84.com/bbs/dm.php?id=487855 A question regarding grid voltages(by Gilles) Hi to you all Long time reader here, first time poster. I'm trying to understand how a tube amp work, component by component, stage by stage. Right now reading Merlin's book about preamp. And to be clear, I'm quite a newbie about the subject, but many thing are becoming clearer since a few weeks (thanks to that great book...) So sorry if my question is basic. Regarding grid voltages, I get that the swing input must be somewhere around 4Vpp max for a 12AX7 if I want my signal to be marginally distorted at the output. But if in a circuit, for example, you have 2 tube stages one just after the other, without almost no attenuation between them, wouldn't the voltage swing of the second stage grid input be FAR above that 4Vpp? I guess that it need to be higher if I want distortion, but how much higher at maximum? To me a signal at let's say 40Vpp, seems to be so much higher that it would result in an over saturated signal, a giant inaudible square. Or is there something I didn't understood, like the signal always being attenuated to smaller value between stages? Thanks for your answer, I'm really stuck on that situation... Sun, 14 Dec 2014 08:19:32 -0500 http://ax84.com/bbs/dm.php?id=487844 FF Boost hum advice needed(by Ben H) Hello, First poster here, long time lurker! I have just completed my first valve amp and decided upon a firefly amp. Sound great on clean but, there is considerable hum on boost. At present I am using 12AX7 for the pre amps and 12AT7 for the output, sounds great. However when I engage boost there is considerable hum. Without boost it is quiet. I have shielded the cable from the switch to the board, tried shielding the signal path through the boost section, but signal just vanished, so back to un screened cable. There is good separation between input voltage and B+ I have moved the valves around and got rid of oscillation that was there to begin with, but can't seem to find out the cause of this hum. I have rotated the output transformer which did not make a difference. I have also swapped valves, but to no avail. I have gut shots, but do I need to host them and will then post a link to them Thanks for any suggestions! BTue, 16 Dec 2014 11:15:43 -0500 http://ax84.com/bbs/dm.php?id=487840 T-driver v3(by The Tone Surgeon) hello im trying to look at this pcb layout and there are 2 components in not sure about the one is in the bottom left corner it reads 00p and appears to be a capacitor the other is slightly up from there it says 10k on it but is too big to be a resistor and has a circle with a line thru it on the corner of it. if someone could enlighten me on what these components are it would be really appreciated. <a href="http://www.aresaudio.com/images/T-driver-V3-DC2-Layout_3t92724a.jpg " target="newwin1418988711">[link]</a> Sat, 13 Dec 2014 09:30:52 -0500 http://ax84.com/bbs/dm.php?id=487830 Smoke!(by winghamwill) Have an SEL which hasn't worked for a little while now, but I started looking at it again, before I was getting a much quieter sound than I should have, now I am getting smoke, and on inspection i can see that the 5k5w resistor is getting red hot... Any ideas what this would be happening? A possible sign of a dud resistor? Cheers WillMon, 15 Dec 2014 03:04:53 -0500 http://ax84.com/bbs/dm.php?id=487827 Custom Picks(by DutchMarco) So I ran acrross this guy the other day: <a href="https://www.etsy.com/nl/shop/ColemanCustomPicks/about?ref=announceAnd " target="newwin1418988711">[link]</a> I thought it would make a cool Xmas gift for a guitar playing uncle of mine. It is actually ather cheap to do, I ordered one with this uncle's name on it, in the Fender font (he's a fan of the Strat) he sent me a sample template to preview how it would come out, and I placed the order. costing me $18 + $1.15 S/H across the Atlantic. Hope it won't get lost in the Xmas mail, fingers crossed! Anyway, thought this would be a nice idea for some of you guys. Happy holidays! (in advance) And, of course, I'm not affiliated with him.Thu, 11 Dec 2014 14:58:42 -0500 http://ax84.com/bbs/dm.php?id=487817 Swapping tubes(by GeoMan) As I mull a build around, I've been considering a 50W power amp. Per the specifications in the building blocks, the design calls for the use of KT77 power tubes. My research indicates that this can be a direct replacement for an EL34. Further research tells me that EL34s can be sort of substituted with 6L6s, with a rebias. Could I simply drop 6L6s straight into the design and make sure it's biased correctly? This seems too easy, but I've been unable to find a really clear answer elsewhere on the intarwebs.Sat, 13 Dec 2014 03:33:40 -0500 http://ax84.com/bbs/dm.php?id=487813 Anyone ever wind their own transformers?(by Darren Porter) Any good guides on how to do this? I know the Internet is full of stuff, but how does someone who's never done it before discern what guide is a good one... so hoping someone here can point me to a good source of info for this. I'd like to try it and see how it comes out. The transformer is really the only part of an amp build that we COULD do ourselves but don't. I know it may cost more, I know it WILL take longer. This is not driven by cost/time savings, etc. It's driven by a desire for more of the amp to be DIY and because I think I might enjoy the challenge. I see that Edcor sells everything I'd need to wind my own.Wed, 17 Dec 2014 14:33:31 -0500 http://ax84.com/bbs/dm.php?id=487812 Voltage divider on signal path(by makaze) Hi, 2 years ago I built a stereo guitar amp using information on here and else where. It has been an incredible home amp and has been used by many players with glowing reports. I recently noticed it's performance was gone, it sort of crept up on me and I didn't notice. I envisaged all sorts of nightmare possibilities. However, a change of power tubes and it's back. I hadn't run a tube amp consistently for an extended period so power tube degradation wasn't something I had been listening for. The loss of performance hit me one day during a noodle session where from playing in what felt like a warm light suddenly I was plunged into a cold atmosphere! During the previous few weeks I had been hitting the amp hard with a homebrew Klon and Honey Bee, hitting some wonderful sounds. Can hitting an amp hard with a powerfull pedal like a klon bring on tube degradation? While looking in my amp for possible clues I noticed that I had a voltage divider between stage 1 and two. Stage 1 is a single ecc83 with the input going to both grids and one output from the anodes tied together, (a marshall 18watt type parallel input stage) this goes to a "gain" potentiometer. On this gain pot I have a voltage divider shunting 50% to ground. I couldn't recall why I did this and searching this site for clues I noticed a mid stage divider on the octane project, which is where I must have pick up the idea. I presume these dividers must be there to ensure appropriate levels are sent to a following stage. Would a parallel input stage require a divider voltage loss before the 2nd stage?. The 2nd stage is a cathode follower ecc83 which the feeds the p1 tone stack, a master volume pot then finishes the circuit. These tubes I use are expensive and I'm fearful of just experimenting by removing the voltage divider in case this bigger signal hurts my power tubes. Does removing or keeping the the voltage diver make more sense? Thu, 11 Dec 2014 05:36:31 -0500 http://ax84.com/bbs/dm.php?id=487801 Does my build (layout) look okay?(by Henrik Lidbjrk) I'm really in the last stages of my Plexi 6V6 build, so it's kinda silly to ask, but I thought I'd do it anyway. Here's a pic of its current state, with everything soldered except the PT and power section: <a href="http://lidbjork.se/amps/6v6plexi_2014-12-10_01.jpg " target="newwin1418988711">[link]</a> The only thing that bugs me is how long all the wires to the tubes ended up, because I put the tube sockets so far to the back away from the circuit board. (It made sense to me when I planned everything in the beginning, but I realize now I should have done it a little differently, with the sockets closer to the middle of the chassis.) Should I be worried about those long wires? Anything else that looks questionable?Fri, 12 Dec 2014 02:52:13 -0500 http://ax84.com/bbs/dm.php?id=487779 Changing overdrive character of a SEL Ė 220K anode load vs. LED/(by Lord of the Livingroom) Has anyone played around with the Anode load resistors and/or LED/diode clipping on a HO or SEL to alter the overdrive character? After checking out schematics of classic amps that I like the sound of Iím after some practical advice. My amp is a 6V6 SEL with Merlinís excellent tube driven serial effects loop in between the tone stack and master volume (modified from the October effects loop). First off Ė Anode Load questions. After looking at Soldano SLO100 and Dumble ODS schematics and reading Merlinís excellent Preamp book about the effects of anode load, the last sentence of Section 1.15 The Effect of Load on Distortion, ďIncreased grid current will result in slightly harder grid-current clipping, which likewise will lead to slightly harder or crisper overdrive sound.Ē caught my eye. Iím wondering about the effect on the overdrive character of my SEL if I change one or more stages to a 220K anode load (and appropriately change the cathode resistor to maintain similar biasing conditions). Has anyone tried this? Secondly - LED/diode clipping. Iíve also been looking at the Marshall Silver Jubilee 2550 LED/diode clipping circuit and toying with the idea of fitting a switched version between stages 1 and 2 or 2 and 3 of my amp. Anyone done this? The overdrive tone of these three amps is highly regarded, so Iím thinking there must be something to these techniques right? I'm not after the exact sound, just a move towards them. It would be great if anyone has any thoughts or experiences to share. Sat, 13 Dec 2014 18:23:10 -0500 http://ax84.com/bbs/dm.php?id=487776 input signal transformer(by DanGu) I've got 2x 140NEX Hammond input mic transformers to sell, which I wrongly bought and don't know what to do whith them. 50Ä each Datasheet here <a href="http://www.hammondmfg.com/pdf/140NEX.pdf" target="newwin1418988711">[link]</a> Tue, 09 Dec 2014 11:27:03 -0500 http://ax84.com/bbs/dm.php?id=487766 C6 failure after 2 years of operation?(by nicadrick) Hi All, What would cause C6 (100uF, 50V) to blow immediately after startup last night? The P1eX has been doing great for the past 2 problem free years. Last night the smoke and stink came out when the component burst soon after powering on. What's me first check? Thanks in advance. RickTue, 09 Dec 2014 17:45:50 -0500 http://ax84.com/bbs/dm.php?id=487758 Assorted Reference Site(by Douche Baggins) Tube, Guitar and Instructional references: <a href="http://www.lh-electric.net/links.html#Refe" target="newwin1418988711">[link]</a> Tue, 09 Dec 2014 14:18:46 -0500 http://ax84.com/bbs/dm.php?id=487756 Stilhaus Kitchens Reviews(by cavendish) I still couldn't get over just how cheap Stilhaus Kitchens are. I was a bit dubious but I didn't pay until after delivery so I had nothing to lose Mon, 08 Dec 2014 21:30:24 -0500 http://ax84.com/bbs/dm.php?id=487754 Questions about a Valve Jr. Layout(by Mike Konopka) Hi, I was gifted a broken Valve Jr. and the poor thing is in sad shape. I'm not even going to attempt to mess with the existing circuit board because it's damaged from arcing and the spade connectors have pulled from the traces in 2 locations. I found some replacement eyelet boards from Watts Tube Audio but when I look at the layout some things struck me odd so I'd like to request a little education as I'm sure there is a good reason for them. So picking this layout: <a href="http://www.turretboards.com/layouts_schematics/vjr/fenderish_mod.pdf " target="newwin1418988711">[link]</a> --- The lower left green wires are running to a existing bolt on the chassis. If you look at the layout, there is a new additional chassis ground connecting c8 + volume pot + R7; wont this potentially create a ground loop? --- Why is C8's negative purposely skipped from the ground connecting C7 and C5? and run to the new chassis ground? -- I saw a note somewhere about using non-isolated jacks for this layout but I remember in my HO build they were all isolated, is the use of isolated jacks and soldered grounds just to prevent the event of a non isolated jack coming loose and loosing it's ground connection to the chassis? Thanks for any help. Mike Mon, 08 Dec 2014 17:18:41 -0500 http://ax84.com/bbs/dm.php?id=487749 Another way to layout your project...(by Henrik Lidbjrk) <a href="http://i.imgur.com/g6muqSR.jpg " target="newwin1418988711">[link]</a> From a 50 year old television set.Tue, 09 Dec 2014 01:43:21 -0500 http://ax84.com/bbs/dm.php?id=487737