AX84 BBS New Threads as of Tue, Nov 25th, 2014 @ 12:48:49 http://ax84.com Amp Parts and KitsDoberman Music Products, LLC offers a variety of parts and kitshttp://shop.dobermanamps.com The secret to a hum-free stand-alone preamp is...(by Darren Porter) .... what??? I've built two now and I'm totally frustrated because they both hum like crazy. I've done other complete builds (one with a layout of my own making) that are hum-free so I _think_ I have a good understanding of a good grounding layout. I do NOT want to go the route of lifting the third prong on the cable either. I want a real, safe solution that also does not require buying a $45 Hum-X or building a clone of one into my circuit (unless that's the only/best solution.) I have other "commercial" preamps that don't hum. How do they do it? My last attempt was Merlin's mid-gain example from his preamp book as a preamp only feeding my Simple Preamp/20W Push-Pull and it buzzes like a hive full of baritone bees. I think I like how it sounds but I can't tell for sure with all the buzzzzzzzzz..... Tue, 25 Nov 2014 11:08:01 -0500 http://ax84.com/bbs/dm.php?id=487561 negative feedback(by Dan Moos) I've never done an amp with negative feedback before, but am now craving the touch sensitivity and guitar control of distortion it enables. I've been looking at these schematics: <a href="http://blueguitar.org/new/schem/trainwreck/wreckxpr.pdf " target="newwin1416937729">[link]</a> specifically schematic "A1b" The NF is, as I expected, applied to the "unused" half of the phase splitter. It is also applied to the cathode circuit of the splitter. Why? My initial guess is it has something to do with keeping the NF from screwing with the bias of the splitter. Is this what's going on? On an unrelated note, in the same schematic, I see that the shield on the input connection is drawn to be connected to the plate of the same stage. What's the advantage to this?Tue, 25 Nov 2014 10:13:36 -0500 http://ax84.com/bbs/dm.php?id=487559 debugging a P1(by mikerl) I purchased a P1 from Chris and just finished the build recently. I have correct voltages at all points on the schematic. The amp sounds good but I have an issue. The volume pot appears to be at full volume (whether I'm getting 100% or not I can't tell) when the knob is at 10 o'clock. When I max the volume knob to the right I get no sound. And, when the knob is fully to the left I get no sound as well (as it should be). So....I assume I have something in the signal chain wired to ground somewhere or the potentiometer is bad or internally grounded at some point??? (Or, not wired properly) I've checked the layout over and over and I think everything is correctly wired. I don't see anything that looks suspicious. Has anyone encountered anything like this? Any suggestions on where to start? I think the volume pot is wired correctly as well as I've checked the volume, TMB, gain, wiring a number of times. Any help or guidance would be appreciated. Thank you!Tue, 25 Nov 2014 11:47:11 -0500 http://ax84.com/bbs/dm.php?id=487553 AX84/Heyboer SE OT Production Run(by Chris Hurley) I've been out of stock on our fantastic Heyboer/AX84 Single Ended Output Transformer for about a year. I don't even have any stashed for myself, so I'm thinking about having another batch made. If anybody is interested in buying one or more of the batch, I'll expand the order. I'm thinking that these will be around $70USD shipped for singles. Multiples might be less... If you're interested, let me know in an email please. Best regards, Chris HurleyMon, 24 Nov 2014 21:36:41 -0500 http://ax84.com/bbs/dm.php?id=487538 merlins serial/parallel looop(by arjepsen) I just put together an october club, and implemented the parallel/seriel loop with a mix pot, as Merlin describes in page 220 in the book second edition of his book. It works well at the pure serial and parallel settings, but when I dial between those two outer settings, the volume decrease to around the middle, and then increase again. I'd love to use this loop and be able to dial in the exact amount of fx I want, but right now that doesn't really work well enough. Any good way to avoid that, so the level would be the same at every setting of the mix pot? Regards AndersMon, 24 Nov 2014 09:28:38 -0500 http://ax84.com/bbs/dm.php?id=487535 What to do with a broken Champ...(by JHarris) Hey all, I messed up and damaged my Silverface Champ's OT. These amps use an RCA connection to the speaker and with corrosion + use, they wear out and can lose connection. If you've been away from tube amps for a while you may keep playing, wondering why no sound is coming out... Rather than checking the speaker right away... Oops. Anyways, I have some options at this point (and some related questions). I'd appreciate any input you can offer. 1. Spend $45 on a Fender or Hammond SE OT plus maybe a new 6V6, and fix it. 2. Fix OT, and replace the rectifier with a 6SN7 to get some more gain, which I would like. 2a. Can the heater and HT windings handle an added 6SN7? What about a different preamp tube that draws only 300ma for the heater? 3. Transistor alternative for more gain... I am not superstitious about a non-clipping transistor ruining the tone, but I think tubes are cool, so if the PT can handle it I'd prefer glass. 4. Spend $35 on a Hammond 125 and rewire everything for a 6SN7 PP output stage plus interesting preamp stuff. Bigger project, maybe high component costs when it's all done. 5. Dig out an ancient PT and OT I have lying around, drop $$$ on a chassis + caps, and build an 85w+ PP EL34 amp that eats EL34s for breakfast lunch and dinner. If I'm going to spend time and money on a build, might as well go big. But, the 2W PP 6SN7 might be better for my apartment. 5a. I had this monster assembled in a sketchy test chassis a couple years ago and got some gross distortion, that I think was blocking distortion. My bias was really low at that point. Like, 10w at idle. I think the B+ was around 600v, if I turned bias up higher is it possible to prevent blocking distortion in EL34s at that voltage? I know I will go through tubes, and I'm willing to push them a little harder because I've already accepted that fact. Don't worry, I don't mess around with NOS tubes in this, I do my part to economically support the Russian new-production industry. Thanks for any advice you can offer! Tue, 25 Nov 2014 03:19:32 -0500 http://ax84.com/bbs/dm.php?id=487534 LEDs for Blues Pre(by DutchMarco) I'm ooking to order bits for my Blues Pre + 20W SE + VVR. I wanted to order bits from here: <a href="http://www.okaphone.com/artikelen.asp?groep=423 " target="newwin1416937729">[link]</a> (because that'll allow me to get the IRF820 for the VVR, too, in one shipment). As you might make out (from the Dutch site), there are several options for red and green LEDs, with a voltage drop of &#8804; 2V and a current of &#8804; 20mA. Are those appropriate?Tue, 25 Nov 2014 10:14:02 -0500 http://ax84.com/bbs/dm.php?id=487528 trouble shooting some unwanted distortion(by cameron nicklaus) man oh man I'm stumped. this is a straight up PR clone...It sounded fine except for when I record it I hear a bit of distortion even at relatively low volumes. I almost can't detect it when just listening in the room but it's pretty obvious through a mic. This may end up being a bunch of questions in one... first off, does anyone have any tips for trouble shooting distortion with a scope? I have a decent one but I'm a bit inexperienced at using it. I can dial in a wave on the screen and can put a sine wave through the amp and see when the wave begins to change shape but I can't recreate the type of distortion I'm hearing with a sine wave...it seems to stay normal way beyond the volume I hear distortion with a guitar at. to try to figure out where it's coming from I bypassed all the gain stages and took the line running into the first gain stage and ran it straight into the phase inverter. so basically; guitar-input jack-gain stage that precedes the cathodyne PI. one really curious thing (that may have nothing to do with anything); at one point the tone stack and the triode after the tone stack was bypassed but I still saw signal on the plate of that triode....so nothing wired to the grid of the triode but still saw AC signal on the plate...how is that possible? would the grid pick up enough just through the air? I had guitar signal coming out of the amp...I thought that, if I disconnected the wire going from the volume pot into that second triode, it would kill the signal? any thoughts or suggestions of things to try would really help!!! Sun, 23 Nov 2014 04:46:57 -0500 http://ax84.com/bbs/dm.php?id=487517 3 Speakers - What to do?(by David E) Hi folks, been a long time. What might I do with three speakers salvaged from an old (solid state) organ? Probably 8 ohms impedance each. I kinda want to build a tweed deluxe, but I haven't built anything for a looong time. <a href="https://www.flickr.com/photos/eggend_houston/15666849580/" target="newwin1416937729">[link]</a> Sat, 22 Nov 2014 12:32:54 -0500 http://ax84.com/bbs/dm.php?id=487512 favorite tone stack(by The Tone Surgeon) Hi im fairly new around here and I was just wondering which tone stacks are your favorite. personally iv always liked the simple tmb controld of my p.o.s. solid state Marshall. but I really don't have alot of experience in the matter.Mon, 24 Nov 2014 07:29:41 -0500 http://ax84.com/bbs/dm.php?id=487508 High pitched oscillation problem(by Kursad K) It's confirmed, I have one: <a href="http://en.wikipedia.org/wiki/Tinnitus " target="newwin1416937729">[link]</a> together with roughly 10dB hearing loss in the bass and treble range. KursadSat, 22 Nov 2014 12:09:46 -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 23:17:29 -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? Sun, 23 Nov 2014 13:54:40 -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="newwin1416937729">[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="newwin1416937729">[link]</a> <a href="http://s906.photobucket.com/user/rexarsenal/media/FireFly/IMG_1727.jpg.html" target="newwin1416937729">[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="newwin1416937729">[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="newwin1416937729">[link]</a> Waiting for inputsSun, 23 Nov 2014 05:59:03 -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="newwin1416937729">[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?Tue, 25 Nov 2014 12:23:56 -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? Sat, 22 Nov 2014 09:55:41 -0500 http://ax84.com/bbs/dm.php?id=487362