AX84 BBS Recent Posts as of Tue, May 26th, 2015 @ 02:57:19 http://ax84.com Amp Parts and KitsDoberman Music Products, LLC offers a variety of parts and kitshttp://shop.dobermanamps.com RE: Merlin's Ultra High Gain (by Lord of the Livingroom) In my amp and stompbox builds I try to follow the basic EMI wiring rules wherever possible (its not always possible, but I give it a red hot go). Rules like; Don't mix high voltage wires with signal wires in a loom, cross wires at 90 degrees to minimise crosstalk, put heater wiring in the corner, etc, etc. It's not hard and solves problems before they begin. Consequently, my builds are quiet; no squealing at high gain settings, no heater/HT hum, etc. (touch wood!) Are there any published rules or essays or papers for P2P in tube amps? How to do it "right"? It's not something I've read about before. So, I'm wondering about the science behind it, and any design/wiring rules to make it work as intended. And if I'm going to build a circuit, I want it to look good. Neat. Messy wiring disturbs my chi.Mon, 25 May 2015 20:35:58 -0400 http://ax84.com/bbs/dm.php?id=490792 RE: Merlin's B9A Board(by Darren Porter) <div class="quoteblock" >On 05/25/2015 @ 17:11, Hank Cohen wrote : I am building my first project with these boards. Very happy about the ease of layout. There is a layout template for diylc but I haven't seen the value of using it. As far as I can tell diylc is just a tool for making a layout picture and not a placemt/routing tool. It doesn't do netlist routing or checking at least not as far as I could see. Maybe I missed something. Anyway no real need with these boards. : : My question for the forum is about the placement of grid stoppers. Merlin's advice for grid stoppers is to place them as close to the tube as possible to the point of soldering them to the socket. What I'm thinking is that one might cut the trace between the socket and track 2 or 7 of the board and solder the grid stopper from the alternate socket hole to the semi-circular track on the board. Seems a shame to cut a track on such a nice board but it also seems like the best way to keep the grid stopper right close to the grid. It also would stop the board trace from acting like an RF antenna. : : Has anyone done this? : : Regards, : Hank -- </div> I don't think you need to do that. I have some pics of my build using these here... <a href="http://www.1darren1.com/2015/03/idea-for-clean-preamp.html " target="newwin1432623443">[link]</a> On the right-most board, going from "12 o'clock high," the third resistor is the grid-stop. If you were doing a point-to-point build, you would be closer by what... 1 cm than this one is? That's not going to make a difference. You just don't want to put your grid-stop resistors on a turret board or even worse your gain knob's wiper and connect it to the tube pin with a long wire. I guess if the board's trace does end up acting like an antenna it would be easy enough to cut the trace but I bet it's not going to be an issue. I didn't use DIYLC to layout my design either. I started to and decided it was pretty much a PITA and did it with a printout of the board and a pencil instead. If I want to share my layout with others, an actual picture of the board is much more useful IMO. I really like the boards a lot.Mon, 25 May 2015 19:59:10 -0400 http://ax84.com/bbs/dm.php?id=490791 RE: Introduction + what to build ?!(by Mitch Markin) The Trinity Tweed Deluxe's power transformer can be wired for either 120V or 240V on the primaries. The instructions say how to do this but they don't show how to make it switchable. It's pretty easy to figure out, though. You just need a double-pole double-throw switch.Mon, 25 May 2015 19:27:45 -0400 http://ax84.com/bbs/dm.php?id=490790 RE: Introduction + what to build ?!(by Darren Porter) <div class="quoteblock" >On 05/25/2015 @ 18:17, Stevo wrote : or the simple preamp (one tube, fender style two gain stage) - <a href="http://www.ax84.com/static/corepreamps/Simple/AX84_Simple_Preamp_Schematic.pdf " target="newwin1432623443">[link]</a> . This, with the 2W push-pull poweramp will get you a low watt clean to mild overdrive amp that you can easily make extremely portable with the right layout and cabinet. You could also wire up an extra power tube socket and get 4 watts output using another tube. </div> I agree that this would be a nice setup. I love my simple preamp into my 20W push pull - it's my main on-stage amp. I don't know about the 2W or 4W though. I think when he gets on stage he will wish he had more power unless his amp is _always_ miced and he _always_ monitors through a floor-wedge or in-ears. Once every six or seven gigs I am finding that I wish I had a little more than 20 watts so I'm thinking of building a 50 watter with Power Scaling. Of course, I also carry my gear in the backseat of my sedan, not an airliner. Mon, 25 May 2015 19:26:37 -0400 http://ax84.com/bbs/dm.php?id=490789 RE: Introduction + what to build ?!(by Stevo) Alright, so from the description of your band situation, I'm getting that you want a low gain, low wattage (push-pull preferred) amp for primarily clean playing (although who doesn't want to crank the gain every once in a while) that is ultra portable with switchable mains (110/220). In that case, I would recommend the clean preamp (two tubes) - <a href="http://www.ax84.com/static/corepreamps/Clean/AX84_Clean_Preamp_Schematic.pdf " target="newwin1432623443">[link]</a> - or the simple preamp (one tube, fender style two gain stage) - <a href="http://www.ax84.com/static/corepreamps/Simple/AX84_Simple_Preamp_Schematic.pdf " target="newwin1432623443">[link]</a> . This, with the 2W push-pull poweramp will get you a low watt clean to mild overdrive amp that you can easily make extremely portable with the right layout and cabinet. You could also wire up an extra power tube socket and get 4 watts output using another tube. With the variable fixed bias controls, it doesn't look like you'd even need to make any circuit adjustments to use an ECC99. Now, some logistics. I don't like the idea of using the diecast enclosures for an amp chassis, and I'd say the 1590BB is definitely too small for what you want. Something like this would be more suitable: <a href="http://www.hammondmfg.com/pdf/1444-12.pdf " target="newwin1432623443">[link]</a> but even this might be a bit cramped for this amp. I'd say if this was your third or fourth build, go for a point to point build. But if you go for a combo amp, you'll probably want a cabinet that can accommodate at least a 10" speaker, so you should have room for a chassis at least 10" wide as well... These OTs are going to be suitable and flexible enough for whatever impedance needs you'll have (some switching may be required). And the 369JX PT should be good for the amp suggestion I've made: <a href="https://www.hammfg.com/electronics/transformers/classic/300 " target="newwin1432623443">[link]</a> Hope this helps!Mon, 25 May 2015 18:17:24 -0400 http://ax84.com/bbs/dm.php?id=490788 RE: HO shuts down with a full volume hum(by Stephen Keller) Given that the seems to operate correctly for 10-15 minutes before the hum kicks in, the problem is possibly heat related. Perhaps, you want to look for something that gets hot and subsequently alters the performance of the circuit: An under-spec power resistor in the screen, cathode or anode circuits around the power tube. A cap too close to a resistor that heats up and causes the cap to drift. A solder joint that heats up and flexes to disconnect part of the circuit. A transformer overheating and drifting out of specification (unlikely). It is probably not a bad socket, given that it happens for both the 6V6 and EL84 sockets. If you can produce the behavior with the components open to examination. Look for something getting too hot to touch. StphMon, 25 May 2015 17:58:46 -0400 http://ax84.com/bbs/dm.php?id=490787 RE: Merlin's B9A Board(by Hank Cohen) I am building my first project with these boards. Very happy about the ease of layout. There is a layout template for diylc but I haven't seen the value of using it. As far as I can tell diylc is just a tool for making a layout picture and not a placemt/routing tool. It doesn't do netlist routing or checking at least not as far as I could see. Maybe I missed something. Anyway no real need with these boards. My question for the forum is about the placement of grid stoppers. Merlin's advice for grid stoppers is to place them as close to the tube as possible to the point of soldering them to the socket. What I'm thinking is that one might cut the trace between the socket and track 2 or 7 of the board and solder the grid stopper from the alternate socket hole to the semi-circular track on the board. Seems a shame to cut a track on such a nice board but it also seems like the best way to keep the grid stopper right close to the grid. It also would stop the board trace from acting like an RF antenna. Has anyone done this? Regards, HankMon, 25 May 2015 17:11:09 -0400 http://ax84.com/bbs/dm.php?id=490786 RE: HO shuts down with a full volume hum(by Chris Linkous) Stevo, it does it with either the 6v6 or the 3l84. I swapped out the first filter cap with the third and it made no difference. Am swapping out the rectifier diodes now. Even after I switch off the standby switch I still hear the hum but at a lesser volume. I will triple check the tube sockets again. You're right about redundancy because I'm obviously missing something! Thanks, ChrisMon, 25 May 2015 13:45:11 -0400 http://ax84.com/bbs/dm.php?id=490785 RE: Introduction + what to build ?!(by Kursad K) <div class="quoteblock" >On 05/25/2015 @ 07:27, Darren Porter wrote : <div class="quoteblock" >On 05/25/2015 @ 03:53, mac dilard wrote : : A few of the songs that were suppose to have been recorded on a Champ: : : Layla, Rocky Mountain Way, Shame, Shame, Shame, La Grange, Cause we Ended as Lovers... : : Just saying : -- : </div> : : If you read the OP's description of what he's after, I don't know how anyone would think a Champ is his solution. </div> I don't know if champ is his solution, but I liked P1 more after I moved the tonestack from its original location to right after the first gain stage. I guess I'd like it even more if I could freely crank it in that way. Based on some other experiments (not necessarily involving any solder, I admit), I have found that basically any blocking distortion free and correctly EQ'd clipping circuit sounds good. So the OT and especially the speaker are important (no wonder that 8" speaker sounds bad as you say), and needless to say, the power tube should not be driven really hard because its grid draws current from the previous gain stage and there is coupling cap in between... To me it seems pretty obvious that it can sound good, even if it might be sounding horrible to some ears as stock. I'm not sure I'd suggest that a beginner should deal with these problems though, even if the actual circuit might be very simple and whatever that might go wrong is well understood. Kursad Mon, 25 May 2015 12:43:45 -0400 http://ax84.com/bbs/dm.php?id=490784 RE: HO shuts down with a full volume hum(by Stevo) The other thing to consider is a bad tube. Since the noise goes away with the power tube pulled, try a new tube. And double/triple check the tube sockets are wired correctly. Doesn't hurt to be redundant here.Mon, 25 May 2015 12:27:56 -0400 http://ax84.com/bbs/dm.php?id=490783 RE: HO shuts down with a full volume hum(by Chris Linkous) Thanks Stevo, I resoldered everything and ohmed out the ground bus from one end to the other. The amp plays beautifully with near zero noise with no input even when dimed. Played for five minutes at a low volume and the BAM the hum started again and went to 1/4 volume when put in standby. I'm probably going to swap out the diodes and the filter caps. There is just no in between phase of this thing. It's perfect until it's the exact opposite. Seems to be happening quicker. Haven't had solder joint probs in the past but that's what I keep coming back to unless it's a component not taking the heat. Family has pulled me off the project for the moment! Thanks again! ChrisMon, 25 May 2015 09:20:41 -0400 http://ax84.com/bbs/dm.php?id=490782 RE: JCM 800 voltages(by mategenomics) Hello, thank for your suggestions, the problem was really with wrong wiring. The amp was in service for two weeks and sounded fantastic for bassguitar on low input and suddenly one day I flicked the stand by switch and terrible hum was there! It is quite loud and static and do not change with vol, preamp vol or EQ adjusting. Its just there everytime the amp is running. I checked BIAS voltage and idle current and everythings ok. Power tubes are not red-plating and show no damage by bare eye. I tried pulling preamp tubes cause I assumed there might be internal short on V3 after master volume but its still there. Voltages seem to be ok and I checked grounding. Still humming. Can it be just power tubes passing away? Other than the hum the amp sounds normal. thank you Mon, 25 May 2015 09:07:17 -0400 http://ax84.com/bbs/dm.php?id=490781 RE: Introduction + what to build ?!(by Darren Porter) Hey Mitch, since you've actually built one, does the documentation come with instructions on how to wire it so that it's power transformer primaries are switchable? If not, I'm sure it's pretty trivial to figure out.Mon, 25 May 2015 07:43:36 -0400 http://ax84.com/bbs/dm.php?id=490780 RE: Adding a gain stage(by Darren Porter) Easy upgrade. I'd put it directly after your Fuzz knob. You could then optionally add another gain knob between V1a and V2a. See the AX84 lead preamp for inspiration. You are almost there already... <a href="http://ax84.com/static/corepreamps/Lead/AX84_Lead_Preamp_Schematic.pdf " target="newwin1432623443">[link]</a> Mon, 25 May 2015 07:34:28 -0400 http://ax84.com/bbs/dm.php?id=490779 RE: Introduction + what to build ?!(by Darren Porter) <div class="quoteblock" >On 05/25/2015 @ 03:53, mac dilard wrote : A few of the songs that were suppose to have been recorded on a Champ: : Layla, Rocky Mountain Way, Shame, Shame, Shame, La Grange, Cause we Ended as Lovers... : Just saying -- </div> If you read the OP's description of what he's after, I don't know how anyone would think a Champ is his solution. Last thing I want to do is turn the OP's thread into a champ flame war, but the fact that you have to struggle to think of a dozen or so songs recorded on a champ means it is a NICHE amp. Now, list all the recordings made with the big 3 - Vox AC30, Fender Deluxe.Twin.Tweed, Marshall... let me know when your hand falls off and I'll let you stop there. :-) Mon, 25 May 2015 07:27:14 -0400 http://ax84.com/bbs/dm.php?id=490778 RE: Introduction + what to build ?!(by Darren Porter) <div class="quoteblock" >On 05/24/2015 @ 21:34, Mitch Markin wrote : I agree with what Darren said. I have a Trinity Tweed Deluxe that I built from their kit. I have other bigger amps, too, but I use the Tweed the most. It's light, very portable, sounds great and it's fairly easy to build. : : Trinity's support, documentation, parts and cabinetry are first rate, too. And they're a Canadian company! -- </div> I thought I saw in the Trinity forums that there are quite a few Trinity players in the Vancouver, BC area. I bet Stephen can point you to some that would be willing to let you hear their amps.Mon, 25 May 2015 07:20:59 -0400 http://ax84.com/bbs/dm.php?id=490777 RE: Jon Fleig's son of F2-B preamp(by Jon Fleig) Chris, If you would like to contact me directly without waiting for me to check the forum, my email is vibrolax at gmail.com I looked for ferrite toroids that might be easier to source in the EU, from Farnell, for example. Farnell does have: EPCOS B64290L0618X035 FERRITE CORE, CYLINDRICAL, 25MM, T35 AL=5400 This would require a few more turns to achieve the required inductance. <a href="http://uk.farnell.com/epcos/b64290l0618x035/ferrite-core-cylindrical-25mm/dp/2355019 " target="newwin1432623443">[link]</a> also EPCOS B64290L618X38 FERRITE CORE, TOROID, T38 AL = 10000. This would require fewer turns to achieve the required inductances. All the formulas necessary to calculate the turns are given on my web pages. The FT-87A-J is sitting on my bench ready to go if you are unable to source it yourself for a reasonable price. Jon Mon, 25 May 2015 07:14:32 -0400 http://ax84.com/bbs/dm.php?id=490776 RE: HO shuts down with a full volume hum(by Stevo) The fact that you used lead free solder shouldn't matter if the solder joints are good. Sounds like when you reinstalled the filter cap, it came close to fixing the problem which tells me you fixed a connection that was questionable. If it keeps coming back as you say, make sure all filter cap solder connections are solid, including the ground connections, and make sure the ground bus makes solid connection to the chassis.Mon, 25 May 2015 05:36:20 -0400 http://ax84.com/bbs/dm.php?id=490775 RE: HO shuts down with a full volume hum(by Chris Linkous) Thanks for the transformer Stevo. I did reflow the screen grid joints as well as the filter cap joints and nothing. I disconnected the first filter cap to check it because I was getting the hum (less of it) Checked out but on reinstall the noise went away. I have the amp on currently for about ten minutes and it just switched to the loud hum and went away after 1 second! I've still got it on and it's quiet. I just noticed that I've been using a new solder roll of lead free solder. Is this stuff no good for this application (Sn99.3/Cu0.7%)? I think it has to be the positive lead on the first filter cap. I'm no soldering expert but cold solder joints have never been a problem in anything else I've worked on. I may just redo it with some 60/40. I didn't intentionally buy this other stuff. The amp is not in shutdown hum now but would be considered a noisy amp. I'm going to redo it now. Thanks guysMon, 25 May 2015 05:11:34 -0400 http://ax84.com/bbs/dm.php?id=490774 Adding a gain stage(by Sirppi) So yesterday I finished building a combination of the EA MV120 preamp stage and the KT88 SE 20W power amp. I'd like to add the unused V1a in the circuit to get more gain out of it, since I have no phase inverter to drive into clipping that the original EA has. Would this be as simple as calculating the right values for the anode and the cathode and putting it in somewhere, or do I need to do major modifications to the whole amp? Here's the schematic I made: <a href="https://dl.dropboxusercontent.com/u/43516629/ampage/vaf.png" target="newwin1432623443">[link]</a> Mon, 25 May 2015 07:34:28 -0400 http://ax84.com/bbs/dm.php?id=490773 RE: Introduction + what to build ?!(by mac dilard) A few of the songs that were suppose to have been recorded on a Champ: Layla, Rocky Mountain Way, Shame, Shame, Shame, La Grange, Cause we Ended as Lovers... Just sayingMon, 25 May 2015 03:53:04 -0400 http://ax84.com/bbs/dm.php?id=490772 RE: Introduction + what to build ?!(by Kursad K) Well, listening to this <a href="https://www.youtube.com/watch?v=BoGbywirzy0 " target="newwin1432623443">[link]</a> I don't think that these sound horrible. Instead: - they sound like they have a very small speaker and a small OT - have almost no preamp distortion and with a bass heavy guitar it seems like they could run into blocking distortion because of high grid current of the power tube. That's all, a simple circuit, and a one trick pony. It can get good at that trick, I suppose. Kursad Mon, 25 May 2015 03:20:55 -0400 http://ax84.com/bbs/dm.php?id=490771 RE: Introduction + what to build ?!(by Kursad K) That's strange, there's no apparent reason that they should sound horrible. Sun, 24 May 2015 23:01:39 -0400 http://ax84.com/bbs/dm.php?id=490770 RE: Jon Fleig's son of F2-B preamp(by Chris84) Hi Jon and thank you very much for your offer. I've found #26 wire and yesterday, I received the answer from a website in Netherlands : they're OK to ship the FT-87A-J to France for less than $6 (including shipping cost). This website is called Kent Electronics; as I haven't heard of it before, I hope they're serious ! If not, I would allow myself to ask your help :-) Have a nice day.Sun, 24 May 2015 22:29:44 -0400 http://ax84.com/bbs/dm.php?id=490769 RE: HO shuts down with a full volume hum(by RickTown) Does it happen regardless of which power tube is installed?Sun, 24 May 2015 22:21:26 -0400 http://ax84.com/bbs/dm.php?id=490768