AX84 BBS New Threads as of Sat, Nov 22nd, 2014 @ 02:00:05 http://ax84.com Amp Parts and KitsDoberman Music Products, LLC offers a variety of parts and kitshttp://shop.dobermanamps.com High pitched oscillation problem(by Kursad K) It's confirmed, I have one: <a href="http://en.wikipedia.org/wiki/Tinnitus " target="newwin1416639605">[link]</a> together with roughly 10dB hearing loss in the bass and treble range. KursadSat, 22 Nov 2014 01:56:58 -0500 http://ax84.com/bbs/dm.php?id=487469 Tube rectifier in a SE amp?(by sajyho) Hi guys, I've recently got interested in 6V6 overdrive tone and I'm gathering information to build a SE amp based on the '59 Supro or maybe a champ. I'm just curious; is there any advantage in using a tube rectifier in a SE amp? I mean since there will not be any voltage sag in a class A amp, so is there any other reason that why should I use a tube rectifier? Regards SajadSat, 22 Nov 2014 00:13:54 -0500 http://ax84.com/bbs/dm.php?id=487462 What should I do with my Peavey Classic 30?(by Darren Porter) I have a Peavey Classic 30 that I used from time to time but I was never totally thrilled with the sound. The clean is just OK and the overdrive makes me cringe. Just not my thing. Now that I have built a few amps I really can't see myself using this amp much anymore because I like everything I've built sooo much better. So I'm trying to decide if I should sell this thing and partially finance another build or gut it and convert it into something I actually like. I don't really see a lot of these on the used market so I don't even know what it's worth. I've had it for about 12 to 15 years but it's in pretty-much perfect condition cosmetically and functionally. Anyone have any experiences converting these to something else using the existing chassis and transformers? Fri, 21 Nov 2014 21:12:26 -0500 http://ax84.com/bbs/dm.php?id=487460 HO Wanted(by brownie772000) Looking for a Big Bottle HO working chassis. Please contact me if you have one for sale. brownieqq3@hotmail.comFri, 21 Nov 2014 03:51:06 -0500 http://ax84.com/bbs/dm.php?id=487456 parts for amps build.(by Elbert Elrod) Need help! would an early 60's Lowrey organ be a good source of parts for a tube amp build? I found one that is in working condition for $50, with internal speakers. Fri, 21 Nov 2014 03:10:53 -0500 http://ax84.com/bbs/dm.php?id=487448 b9a Prototyping board(by Chris Hurley) Merlin was gracious enough to allow me to have some of his awesome 9-pin prototyping boards made. They have arrived and if anyone in the USA is interested in getting one or more, let me know. These are very unusual and very interesting. If you aren't aware of them, check them out: <a href="http://www.valvewizard.co.uk/developmentboard.html " target="newwin1416639605">[link]</a> I was immediately intrigued. Drop me a line if you're interested in these as I am. -Chris Thu, 20 Nov 2014 10:32:22 -0500 http://ax84.com/bbs/dm.php?id=487443 New High Pitch Squeal-Help!(by Eric Nelson) I stored my Firefly in the attic while out of town for about two months this summer and when I got it down and played through it it had a high pitched squeal that I've never heard before. The amp is 4 years old now and has always worked fine. I'm sure the amp didn't get wet or anything like that but it does get pretty hot in attics in southern Arizona in the summer. I tried different tubes in all three locations, tried different guitar and speaker cables, and tried different guitars..with no effect on the squeal. It does not happen when I have the boost switch off...I can turn that gain knob all the way up with no squeal. However, when I switch on the boost it starts to squeal when both gains get up to about 50%. I've checked what I could on the board and tightened up all the connections with no luck. Can anyone help troubleshoot this fine little amp? Thanks much <a href="http://s906.photobucket.com/user/rexarsenal/media/FireFly/IMG_1726.jpg.html " target="newwin1416639605">[link]</a> <a href="http://s906.photobucket.com/user/rexarsenal/media/FireFly/IMG_1727.jpg.html" target="newwin1416639605">[link]</a> Thu, 20 Nov 2014 18:54:37 -0500 http://ax84.com/bbs/dm.php?id=487429 Bias setting for 2W SE power amp(by Greg Smith) I am finishing up a small amp build using the 2W SE power amp design from this site. I'm a bit puzzled by the plate dissipation ratings for the 6SN7 tube. Datasheets indicate a 5W max dissipation for each triode half, but only 7.5W when both halves are driven together (as they are in the 2W SE amp). Would have thought it would be 10W max dissipation for both halves. Is this a heat consideration? I'm trying to determine if I should adjust the bias to 90% of the 7.5W rating, or 90% of 10W. Right now, I have it set to the former, but not sure if that's optimal.Wed, 19 Nov 2014 10:56:30 -0500 http://ax84.com/bbs/dm.php?id=487411 mic preamp hum(by DanGu) Hi. i've finished a tube mic preamp for a friend who has to record some tracks. But testing it we noticed that the mic inputs have to much hum for recording purpose. Here the schematic of the input grounding: <a href="http://postimg.org/image/5tuka6b7x/ " target="newwin1416639605">[link]</a> This has about 60dB of gain. The instrument input is after the signal transformer(hammond 140NEX), has about 50dB of gain and it's not so noise. The amp chain is Ham_140NEX->12AU7->12AU7->ecc88->CF ecc88 We tryed to connect the pin 1 gnd directly to the case or lift it without success The heater supply is 12.6VDC and elevated at about 60VDC Power supply transformer is an hammond 370ax, and used a choke 155G for filtering the power supply I'm wondring what else I can do to make it quieter. I'm starting to think I my have bought the wrong input transformer Here a pic by the way <a href="http://postimg.org/image/t3rolqz3n/ " target="newwin1416639605">[link]</a> Waiting for inputsWed, 19 Nov 2014 19:32:26 -0500 http://ax84.com/bbs/dm.php?id=487390 legacy preamp questions(by The Tone Surgeon) hi.. this question is way out of my league so as your answering just know that you don't have to be worried about some newb attempting this. it's purely to settle my own curiosity/ maybe teach me about how in-depth this hobby can get I'm looking at a schematic I stumbled apon for a 1st generation carvin legacy. which got me thinking how hard would it be too take this preamp and pair it with a 20w push/ pull power amp. the amp is normally 100w I guess my main question is how much would someone have ti change the preamp schematic. or if this would even be a realistic project. not for me at my present experience but a few years from now perhapsFri, 21 Nov 2014 13:56:27 -0500 http://ax84.com/bbs/dm.php?id=487389 Turret Board for Blues Jr.(by S1vaD) I thought some of you might find this interesting. Doug Hoffman has a project where he is putting together a drop-in turret board and a tube socket mounting board for the Blues Jr. You can check it out here: <a href="http://el34world.com/Forum/index.php?topic=17845.0 " target="newwin1416639605">[link]</a> Tue, 18 Nov 2014 10:31:10 -0500 http://ax84.com/bbs/dm.php?id=487386 Mods for more gain?(by Caprotesta) Hi all, I recently converted my P1 to a Hi-Octane. I'm a high gain guy, and the difference in gain is quite noticeable. This small conversion project got me to thinking about trying to get more gain out of a couple of other amps I have laying around. Does anybody have any good resources for reading up on different techniques to do this? I've read the theory documents for the P1 and Hi-Octane on the gain, but the other amps I want to mod out aren't as simple and don't have the same configuration. Both already have two 12AX7s. I think adding another preamp tube might be overkill. I would think that there should be a way to get more gain out of what I already have. Does anybody have any suggestions? Wed, 19 Nov 2014 18:19:07 -0500 http://ax84.com/bbs/dm.php?id=487384 Best way to wire the heaters?(by Henrik Lidbjrk) Next step for me is to solder the heater wiring, and I'm deciding whether to use the PT heater center tap or instead solder 100 ohm resistors between heaters and ground. For example, on EL34World.com, it says "I actually prefer the two 100 ohm resistor method because they act like fuses if a power tube plate wire ever shorts out from pin 3 over to pin 2. Pin 2 is one of the heater wires and is a direct short to ground for the high voltage that is found on pin 3. This happens all the time and you can save your power transformer by having the pair of 100 ohm resistors instead of a transformer center tap. The 100 ohm resistors will melt in half if the plate wires ever short out to pin 2. This is way cheaper than replacing a power transformer." What do you folks think about this? It sounds like a good idea, but it feels stupid to not use the PT center tap when it has one. If I decide to use the resistors, exactly where at ground should I connect them? (I'm using a bus ground system.) And I suppose I ain't supposed to use BOTH the resistors and the PT center tap?Fri, 21 Nov 2014 06:26:20 -0500 http://ax84.com/bbs/dm.php?id=487370 Thinking about doing a Lead II(by Denny Gracey) OK so it's only been a week after I finished up the SEL which I absolutely love - and need another project. Thinking about building out a "lab" amp - use a turret board so I can easily change components, install an extra couple 9pin sockets and another octal (in case i wanna do a PP), etc. The Lead II looks interesting - might start with the L2L (Brian's) - his clip sounds pretty darn sweet and it's basically a modded SEL. I don't "need" another amp - I need another project to keep learning and having fun with this. Yeah, I'm hooked. Suggestions/ideas appreciated. Mon, 17 Nov 2014 05:02:53 -0500 http://ax84.com/bbs/dm.php?id=487363 rhythm/lead switch question(by Denny Gracey) Installed the rhythm/lead switch in my SEL - seems to work as expected with one nuance- when in 'clean' mode (bypass gain stage 3), the gain 2 knob must be at zero otherwise the signal attenuates as i turn up gain 2. From the schematic it would seem that gain 2 knob is completely bypassed. Is this normal or do I have something wired wrong? Here's the way I wired it: * pole 1 to V4 pin 1 * pole 2 to V3 pin 2 * pole 3 to V3 pin 6 comments anyone? Fri, 21 Nov 2014 21:56:25 -0500 http://ax84.com/bbs/dm.php?id=487362 DIY High voltage, High current power supply(by Greg Robinson) Hi everyone. I picked up a big, beefy transformer recently, it's 1kVA, and meant for industrial settings to allow 115/230V equipment to be used on any number of different supply voltages, so has a number of primary windings (configurable for 208V, 230V, 380V, 400V, 415V, 440V, 460V, 480V, 500V, 525V, 550V, 575V & 600V). The secondary is 2x 115V for 115V or 230V equipment. Here's the datasheet: <a href="http://www.farnell.com/datasheets/1648839.pdf " target="newwin1416639605">[link]</a> I'm planning on running it backwards (it is an isolation transformer, not just an autotransformer), so that I can get a number of different high voltages, and build a bench power supply around it. I'm planning on using a microcontroller to control it, using relays to select the operating voltage of the transformer, and an emitter follower output (controlled with an optocoupler) to control the voltage (using a 10 bit PWM for 0.5V steps). I'm hoping to get a number of adjustment ranges from 200V up to 800V, at 1A max current (stupid amount of power, I know). I don't want to bother with a constant current control. I've designed it with 8 parallel output devices to help keep individual dissipation down and reduce junction to case resistance so that I won't need liquid nitrogen to run the damn thing. Here's a link to my design as it currently stands: <a href="https://www.dropbox.com/s/yimf2gx8wzd0850/HIGH%20VOLTAGE%20POWER%20SUPPLY.pdf?dl=0 " target="newwin1416639605">[link]</a> I haven't started prototyping it yet, but I'd really appreciate any comments, insights, suggestions, or especially the pointing out of any obvious flaws! It's going to take me a while to justify purchasing all the parts, so I think I'll just be tacking bits and pieces onto other orders for a while... Might be a LOOONG time before anyone gets to see this completed!Mon, 17 Nov 2014 10:04:48 -0500 http://ax84.com/bbs/dm.php?id=487347 Valve Junior Part and More!(by SX4Amps) <a href="http://www.ebay.com/itm/171541848664 " target="newwin1416639605">[link]</a> For Sale is a large lot of Epiphone Valve Junior parts plus much more! This lot would be ideal for any guitar amp builder. I have accumulated these parts over the last several years from modding and building. The Epiphone Valve Junior parts are PCB's, lighted on off switches, speaker and input jacks, hardware and screws, and wiring. Also in this lot are several 9 pin and 8 pin tube sockets, tube shields, tube retainers, pilot lights, and strain reliefs that will work on any tube amp. Some parts will be included that are not in the pics because I could only include 12 pics! The parts are a mixture of new and use parts. Fri, 14 Nov 2014 02:17:54 -0500 http://ax84.com/bbs/dm.php?id=487344 HO SEL FINISHED!(by Denny Gracey) For all practical purposes, this is my first "real" build. I'd built an 18watt using the Baby Will PCB, which was like painting by the numbers vs this project which was more like having a canvas and bunch of paints. Chris sent everything I needed, including, to my surprise, a blank chassis. I didn't plan on punching my own chassis but that turned out to be lots of fun - thanks to the amazing step-bit (never heard of such before this project). I studied Mitch's SEL build pics which were a huge help, and except for a faulty input jack (which took me 3hrs to troubleshoot), this baby fired right up. And what an amazing little amp this is! Problem is I'm hooked on building and plan to sell my 'production' heads to pay for more builds. For whatever it's worth to others new to building, a few bits of advice I picked up on this forum that lead to a successful build, and made the project such a rewarding experience: * Read the theory paper; then again; and if you're like me, by the third read you'll have enough of the basics to appreciate the schematic (I'm still trying to grasp the cathode follower but it works!) * Study the schematic and layout with the goal of being able to explain to your buddies what each component does * If you've never soldered eyelets, they are bigger than PCB's so practice topping them off so you'll get a feel for how much solder to use for solid connections * Study pics from other builds by pros like Mitch, keep your wiring tidy so it's easy to trace * Trim your wires AFTER you install the board otherwise you'll likely end up splicing a few (like I did) * Trace the circuits with an ohm meter to confirm all the components are connected as they should be, and no shorts. A few pics of the project, from creating the chassis template out of orange poster board (left over from one of my kid's school projects), thru finished amp. Any comments/critiques from the veterans would be much appreciated <a href="http://s368.photobucket.com/user/dboy5150_2/media/photo2.jpg.html " target="newwin1416639605">[link]</a> <a href="http://s368.photobucket.com/user/dboy5150_2/media/photo3.jpg.html " target="newwin1416639605">[link]</a> <a href="http://i368.photobucket.com/albums/oo121/dboy5150_2/photo6.jpg?t=1415840244 " target="newwin1416639605">[link]</a> <a href="http://i368.photobucket.com/albums/oo121/dboy5150_2/photo5.jpg?t=1415840254 " target="newwin1416639605">[link]</a> <a href="http://i368.photobucket.com/albums/oo121/dboy5150_2/photo4.jpg?t=1415840249 " target="newwin1416639605">[link]</a> <a href="http://i368.photobucket.com/albums/oo121/dboy5150_2/photo1.jpg?t=1415840222 " target="newwin1416639605">[link]</a> <a href="http://i368.photobucket.com/albums/oo121/dboy5150_2/photo.jpg?t=1415840228 " target="newwin1416639605">[link]</a> Thu, 13 Nov 2014 13:28:55 -0500 http://ax84.com/bbs/dm.php?id=487330 Pre instability?(by hyp3rv1p3r) Hi all, yesterday I was showing a friend how quite is my P1-eX without any guitar connected and, surprisingly, with all master up and gain at 3/4 a sort of feedback (larsen?) started. After some testing I think that the problem is related to the first stage and if I remove C16 it disappears. Also it is absent when a guitar is plugged. I have tried to change C16 with a smaller and larger value cap but the problem persists. Any idea? What am I missing? Should it be related to cathode bias resistor? Thank in advance for your help. Ant p.s. Without C16, as expected, I have a low gain.Wed, 19 Nov 2014 23:37:31 -0500 http://ax84.com/bbs/dm.php?id=487326 Getting started and free resources(by stevelvd) Hey everyone, I'm starting my first amp project (got a P1 kit from Chris @ Doberman) and doing a lot of reading! First, thanks for all of the great info here! I also got some great Navy manuals from my Dad (can't believe he still had them) and I found copies available online for free so I thought I'd share with anyone who's interested. Here's the link: <a href="http://onlinebooks.library.upenn.edu/webbin/book/lookupname?key=United+States.+Bureau+of+Naval+Personnel " target="newwin1416639605">[link]</a> Here are two of the manuals I've started with: Basic electronics. Prepared by the U.S. Navy Training Publications Center. (Washington : The Bureau, 1962) Basic electricity / prepared by the Bureau of Naval Personnel. (Washington : For sale by the Supt. of Docs., U.S. Govt. Print. Off., 1960 [i.e. 1961])Tue, 18 Nov 2014 10:24:22 -0500 http://ax84.com/bbs/dm.php?id=487313 Added Merlin's "Scale Control" to my Simple/20WPP(by Darren Porter) I wired-up a 50kB pot as shown in his "Figure 9.16A" method. For some reason, this really made this amp come alive. It doesn't quite get down volume-wise as much as I'd hoped but man it sure has a MUCH more pleasing overdriven tone. I'm wondering how such a change would take this from an amp that was pretty much only good for clean tones (very good that is) to a _very_ nice sounding overdrive. So much nicer in fact that I think my 18 Watt Lite IIb just got replaced as my favorite for overdrive. The circuit used is the Simple Preamp into the 20W Push Pull, both without any changes except I removed the standby switch to make room for the Scale pot on the front panel and I replaced the R23 470R with the scale pot. It was such a simple change (mainly because I didn't have to drill anything) that I recommend trying it out.Wed, 19 Nov 2014 15:08:41 -0500 http://ax84.com/bbs/dm.php?id=487311 AC30 Transformer set for sale(by jason d) I've got power, output, and choke for an AC30 for sale. They came from Hoffman Amplifiers and were part of an old build that was taken apart. Some of the leads have been clipped but there's still plenty left to splice on extra length if needed. There's also some rust because they've been sitting in my garage for about 8 years but nothing too bad. I'd like to get $100 for all 3 and I'll ship them whatever is cheapest if you're in the continental US. If your local to Rancho Cucamonga in S.California and want to pick them up it'd be cheaper. Email me at jrdworak at yahoo dot com if you want pictures or are interested. If I don't hear from anyone in the next few days they'll go up on ebay but I hope not. I hate their fees. If you want to check out my ebay feedback my seller ID is jrdworak. Thanks guys and happy building.Thu, 13 Nov 2014 17:37:44 -0500 http://ax84.com/bbs/dm.php?id=487309 reverb tank(by The Tone Surgeon) hello everybody this is my first post on here.... before I start I want to make it clear I don't know what I'm doing yet and I have no intentions of starting a build soon, I have alot of learning to go still before I begin. with that being said this question is just to help me understand how things work together. iv been searching Merlin s website and I stumbled apon this <a href="http://www.valvewizard.co.uk/reverbdriver.html " target="newwin1416639605">[link]</a> my question is where in the power amp section does this go. my guess is after the output transformer right before the speakers, our is it it's own circuit something that would go In life an effect chain. - thanks In advance for any responsesSun, 09 Nov 2014 10:04:06 -0500 http://ax84.com/bbs/dm.php?id=487275 show me your prototyping rigs(by Dan Moos) The biggest frustration I've found when designing amps is that it's such a lot of work to do what is simple on a breadboard with solid state. I feel the need to finally build a good prototyping rig, probably with some sort of variable power supply. Not wanting to re-invent the wheel, anyone want to show me what they use?Mon, 10 Nov 2014 12:54:07 -0500 http://ax84.com/bbs/dm.php?id=487274 Output transformer question(by Darren Porter) I am looking at a push-pull reverb driver circuit that uses a 12AT7 in self-split/LTPI mode, kind of like the one in my PP-Reverb unit based on the FireFly, but a little different. The tank driver transformer is supposedly a 150k primary to an 8R secondary. Between the two primary-to-anode leads is a 33k resistor, basically in parallel to the transformer and the anodes of the 12AT7. The recommended tank is an 8R input/2k-to-4k output. If I did my math correctly on parallel resistances, it works out to about 27kR, which is not that far from the Raa value of a 12AT7 of somewhere around 21k or so. How does this look on the other side of the transformer? Is it still going to be 8R or does the turns ratio mess with things on the output side? Instead of paying about $50 for that transformer, I have a Hammond 125A laying around and if I wired it for 22k-to-8R (leaving off the 33k resistor) will I get similar results to the original circuit using the same reverb tank (which I also have laying around)? I'm sorry I can't post a schematic it's from a non-public-domain book and has not been published to the web as far as I'm aware. Tue, 04 Nov 2014 14:47:29 -0500 http://ax84.com/bbs/dm.php?id=487237