AX84 BBS

Amp Parts and Kits

Doberman Music Products, LLC offers a variety of parts and kits

Pedal mod solder iron temps?(by RickB)

Fri, 19 Mar 2010 18:29:26 -0400

Just ordered a mod kit for my boss GE7 pedal. I have an adjustable weller soldering iron. What watts should I use for working on guitar pedals?

VVR for 5F1(by DutchMarco)

Fri, 19 Mar 2010 17:32:15 -0400

[Note: posting again, I can't seem to find the post I made a few hours ago, so something must've gone wrong, dunno what] Hi all, so I'm almost entirely on the saxophone path right now (replaced my cheap Chinese alto with a more expensive (+ better?) tenor, but I've been thinking: I have this cool Vamp: a 5F1 champ with a 12" speaker, an amp which I adored (but not all band members at the time did, as I had the habbit of enjoying distorted playing, which can get loud in a rehearsal room, even with a 5W tube-amp, as you know). So I've been looking into adding VVR (perhaps with fixed attenuation level? On a switch then) In other words I'm looking for a (PTP-) schematic. I've found hallamplification.com, but not that. I'd like to make it myself dof buyinig their PCB. But I can't seem to find the schematic anywhere on the interwebs. could anyone help me withthis?

Do I have a one watt resistor?(by RicardoGomez)

Fri, 19 Mar 2010 19:24:31 -0400

Well, I've been surprised at how much I'm learning just from assembling the amp, and I haven't even picked up the soldering iron yet. Needless to say, I've learned tons from lurking around here for years. At the moment, I've installed all the hardware in the chassis, and I'm loading the components in the eyelet board. I'm very close to picking up the iron. I had one question that I haven't been able to answer by looking through old threads, looking at other people's build pictures, or searching the internet. I bought the P1 kit from Chris a long time ago. It came with three 100 Ohm resistors, as expected. One of them is supposed to be a 1 Watt for the power supply (R5 on the schematic I'm using, if I recall). However, they are all the same power rating. They do not resemble the other power supply resistors that I assume are one watters - the slightly larger gray ones. The 100 Ohms are darkish blue, matte surface, medium sized, resistors that match most of the other resistors in the kit. Are these actually rated at one watt, or do I need to get a different 100 Ohm resistor? If that's not descriptive enough, I'll try to post a picture this weekend. Thanks, Ricardo

Dragonfly Builders, Please Read This(by Doug H)

Fri, 19 Mar 2010 14:45:44 -0400

Over the last day or two I uploaded some bogus changes to the schematic. I have it all straightened out now. You can get the correct schematic here: [link] The power transformer is a Hammond 269JX. You can run the ECC99's at a higher voltage than the 12au7's in the Firefly- plus there is a sag resistor that drops the voltage somewhat. So I'm using a 250-0-250 xformer in this one. Also, I accidentally changed the Rk's back to 220, which is the "Firefly ECC99 value". That's *incorrect*. Due to the higher voltage, etc, the Rk's are in fact 430's. (I verified all this with the photos.) I need to do some voltage tests on this and add them to the schematic as well. Sorry about any confusion. Didn't have my act together when I started posting schematics for this amp. (Been a couple years since I built it.)

Ensureing I'm running with the correct impedence on the october(by RickB)

Fri, 19 Mar 2010 16:52:23 -0400

Hi all.. I'm running two 10" Ragin Cajuns. They are 8ohm each. They are wired in series at the moment, should I be running my amp with a 16ohm impedence? Then, if I want to run them in parallel, I run them on 4 ohm impedence?

Micrphonic Squeal(by 3rdof3)

Fri, 19 Mar 2010 19:09:55 -0400

I have read all I can on here about squeal and am curious if it can be caused by having too little attenuation between the gain stages? IE: 5 stage + CF preamp into AX84 SE power.

even and odd(by nonzero)

Fri, 19 Mar 2010 18:38:49 -0400

Hey kids. A friend of mine and I are working on building an amp, and a question came up: Is it possible to set up a preamp or a power amp section to emphasis either even- or odd-order harmonics?

Firefly without standby switch(by LuisG)

Fri, 19 Mar 2010 13:18:17 -0400

I want to build a Firefly without a standby switch Is this advisable? can I damage the tubes? I just want to bypass the switch line on the PCB. Thanks Luis

P1-ex is a bit too trebely (by LuisG)

Fri, 19 Mar 2010 15:44:53 -0400

Hello guys, My P1-Ex sounds great, but the trebble pickup from my gibson sounds a bit too reblely for my taste. What can I change to make it a bit less trebely? caps/resistors? in what range? Thanks Luis

P1-EX build complete! well don't think so(by LuisG)

Fri, 19 Mar 2010 04:19:46 -0400

First of all I want to thank everyone who helped me get my build up and running, the amp should be dead quiet if it wasn't for my guitar. I tried it with the iphone at no volume and 1 click volume and at max gain/volume and it was dead quiet, only hiss :) So its done but no there yet... Today I installed VVR and its working... Next I will install a switch to be able to cathod bias for the other set of recommended tubes. I am considering a FX loop mod to install reverb using a cheap pedal but I will leave this mod for a later time [link] the plan would be to disassemple the pedal and stick it inside somehow... I am in no hurry and mount the controls on the chassis. Thanks again for all the help, Luis

Any wesite ad experienec?(by Miles ONeal)

Fri, 19 Mar 2010 11:17:33 -0400

If any of you have web sites or pages funded by ads, how has that worked for you? What do you do-- use Google AdSense, or sell ads directly like Chris, or what? Also if you have a web site that asks for PayPal (or similar) donations, what did you use and how has that worked for you? Thanks, Miles

Same problem with every amp i build(by Martn Redolatti)

Fri, 19 Mar 2010 19:45:14 -0400

I must be missing something, but every amp I build seems to have this really annoying high frequency precense that just makes the amp sounds awful. Happened first with an 18 watter, so I thought "hey it's this horrible EL84s, let's try other tubes", build a 6l6 push pull P1, same thing, now built a dual channel amp high gain on one side, DR103 preamp on the other... and guess what, it has the same high trebly notes that make the amp almost unplayable. I ALWAYS end up putting big caps (22nf on the 18 watter, 5uf on the PP P1, 10nf on this one) across power tube grids right before grid stoppers. which tames a little this annoying thing, but at the same time makes my amps sound rather dull and uninteresting... I'm currently thinking of: Poor quality parts? Poor layout? OT meant for HIFI? I know many people use this OTs and most sound good, and I tried MANY, beleive me. Thaks for taking the time to read

Buzz analysis help please(by Lou Glorfeld)

Fri, 19 Mar 2010 00:12:01 -0400

I'm trying to get rid of excessive amp buzz on my HO. I set up my o scope that I have not used in four years and tried to trace my signal by looking at the grid signal, guitar plugged in but volume off. I had no trouble finding a signal for the guitar or function generator on, but the buzz signal was *very* week in comparison. So tonight, I set the Volt/Div to 5mv and the Time Div to about 2ms. This is the scan that I got: [link] Please excuse the blurry image but you should get the idea. I am not very o scope knowledgeable, so I don't really no what this means, but I'm getting spikes on the second preamp grid, and the third preamp grid, which is what you see in the pic. I may be getting them on the first preamp grid but just can't detect them. The size of the signal and the spikes is of course dependent on the gain control settings. Any help would be appreciated.

small combo(by danhei)

Fri, 19 Mar 2010 11:57:12 -0400

This is my most recent build. My dad made the cabinet. It's African padauk, which has such a wonderful red color. front: [link] top: [link] rear: [link] Tubes are 6BK5 output and 12AX7 preamp. Controls are volume, Roy Bean tone controls, and VVR (on the 6BK5 screen only). Has a 1966 Jensen C8R pulled from an old organ. The combo is quite compact, sized to fit the speaker. I wanted something about as small as I could get with an 8" speaker. Output is about 3W so it's for practice and jamming with a buddy or two. The VVR is really nice for getting the power tube distortion down to bedroom levels. The silver grill cloth isn't really as see-through as the flash made it look in the pic. The jack on the rear is for an external speaker. It was pretty tough working in such a small chassis!

Hi voltage SS FX Loop(by Martn Redolatti)

Fri, 19 Mar 2010 12:17:52 -0400

Hi everyone. I'm sure this topic has been already discussed but i didn't find much while browsing. Just someone who built reverb driver/recovery stages using LND150s. I was thinking of send/drive and return/recovery stages using IRF820s. AFAIK I could do the driving stage in a similar way to a cathode followe. I would be 100k + 1 K in the source (with the send signal taken from a bypass cap connected between both resistors. Drain connected to B+, what about the gate? with the IRF820 being a N-Channel MOSFET, it should be conencted to a pull-down resistor to ground, or am I missing something? Also, any idea about the recovery stage? Just a normal gain stage with say 1k5 in the source, 100k in the drain? Thanks a lot in advance guys!

log pot math(by John Hannon)

Thu, 18 Mar 2010 16:05:08 -0400

I need to replace a 1M audio pot with a 6-position rotary switch--so, 5 resistors that add up to about 1M, and are stepped in such a way as to more or less approximate the audio curve. Can anyone tell me what the math for that would look like?

12DW7/ECC832 Direct coupled gain stage to cathodyne(by Brad Montgomery)

Fri, 19 Mar 2010 19:36:14 -0400

Merlin's book has really illuminated this topic for me and so far have found the [properly tweaked] cathodyne to perform brilliantly in a hot-rodded/highly modded 5E3 context. I reversed the triode wiring on V2 to use the 12AU7 side of the ECC832 for the cathodyne which really broadens the bandwidth response to my ears. I would next like to try direct coupling and have seen examples of using 12AU7's and 12AX7's but not the 12DW7 and wonder what considerations have to be made for it to work successfully. What say the learned?

My guitar hums loud(by LuisG)

Fri, 19 Mar 2010 12:09:53 -0400

Hello guys, After much troubleshooting my P1-EX I finally know it works (ipod at one click volume has no buzz/hum). My guitar is a Gibson Les Paul with Seymour Duncan Alnico II pickups. I have 2 guitar cables a cheapo and a Monster cable. It hums/buzzes with both. I tried 2 other amps with my guitar and it hums and buzzes with them. I opened the guitar and did not like what I saw :/ so I did a complete rewire of it. Plugged it back in and still hums, I used shielded wire everywhere except for the ground. So I took all the electronics out of the guitar except for the neck pickup and the guitar input jack. I then connected the pickup into the jack directly, so I conected the ground and the hot line and also the ground from the guitar neck. I plugged the guitar into the 3 amps (One in one room and 2 in another room) and it hums/buzzes still. So I intalled the bridge pickup and removed the neck pickup and did the same thing and it also buzzed. So I went and removed the pickup and installed the original gipson pickup and again it buzzes/hums. My guitar is Cursed! :P So I only have the pickup wired to the jack and the ground from the neck (tried with and without it). So Ground of the pickup with ground of the shielded wire + ground of the neck on the ground terminal of the jack and the singal wire on the hot terminal. And always hums! Nothing else is there except wood. Last thing I tried was using an external input jack to discard the guitars jack and it made no difference. No fluorecent lights, nor computers on the rooms. So what in the world is going on :/ these are humbuckers! How can I quiet the beast? Thanks Luis

Troubleshooting time(by Dust Puppy)

Thu, 18 Mar 2010 17:22:33 -0400

After placing my P1 into a cab, I now find that the mid pot is dimming the mid range when I turn it up. If I turn bass and treble down and dime the mid, I get nothing.I have a couple of gut shots Here [ [link] and here [ [link] Please take a look at it and let me know if you have any ideas. I'm not seeing anything obvious.

HO conversion to SEL(by Todd G)

Thu, 18 Mar 2010 15:51:40 -0400

I have a HO build that I want to bump up to SEL and see if I can use a EDCOR PT/OT set to do it. I am wondering if edcor XPWR051 power transformer 330-0-330 is to much B+ for the SEL? Here is a link to specs. [link]

Parts Sources(by 3rdof3)

Thu, 18 Mar 2010 01:38:54 -0400

Without trying to shill for anyone, let's get some vendors listed for us newbs that have caught the bug and get a bit daunted at sourcing everything via google. My fav's are: -Small Bear Electronics -CE Distribution (must have TaxID) or Antique Electronics -Watts Tube Audio -Handmade Electronics -Mouser -Hoffman Amps -Doberman What are yours?

Per Merlin's Web site, Push Pull section(by KyleJ)

Wed, 17 Mar 2010 21:24:59 -0400

Assumptions: JJ Tesla EL34 (using the graph based on 250V screen) Plates at about 420V Screens at about 250V OT - 6,600 P2P Based on Merlin's technique I come up with a bias of about -20V. The plot of 420V / (1/4*6600) goes right through the knee at grid = 0V Right now the design has a choke, but that won't drop the 170V to get the screen voltage, a power resistor aprox. 2k6 would be more appropriate. Am I making sense?

Strange noise issue(by SlashLP97)

Thu, 18 Mar 2010 13:45:40 -0400

So I'm homebrewing my own tube amp of custom design, which is also my first amp build.. ever (I wouldn't recommend anyone else doing this, as with no experience it has been nothing but frustration and pain). I am finally at the last few steps of the assembly and I was testing the output of the PI (standard cathode fed deal, as in any Marshall or Mesa) and I seem to see some strange noise that looks like AM radio (low frequency carried by high frequency) however it is fairly stable, forcing the assumption that it is NOT radio, as that would involve broadcasting more than two sinusoids multiplies together. Has anyone else ever seen this behavior, this is ONLY at the output of the PI (both cathodes), and the rest of the amp is quiet as a mouse. also, the amp is upside down with the exposed chassis innards facing up, so it is very susceptable to noise, ultimately I will have it mounted in a head cab with an aluminum sheet under it, acting as a cage with the chassis itself. Also, the power tubes are not connected, I have gotten as far as connecting it to the bias voltage adn that is it. Any ideas, or should I not even worry for now?

To choke or not to choke(by Martn Redolatti)

Wed, 17 Mar 2010 16:43:48 -0400

Hi everyone. I finished an amp not long ago which sounds really nice (to me) at lower-moderate volumes, but starts to sound too mushy at highwer volumes, I mean, notes lose clarity, and bass becomes too boomy. I read a recent thread of Doug H modifying a windsor amp to JCM800 preamp and PI, and how adding a choke helped improve this things. I currently have a 220-12V trannie (primary) wired after plates and screens, before the PI and preamp, in an old attempt to build a hot cat-style amp. Such trannie measures about 3H according to my multimeter. I have the possibility to buy a 200ma 10H choke from a guy who builds transformers. Do you think it will improve the overall sound (and make things a bit more clear) if I put one of those between plates and screens, etc the way most amps use it? Thanks a lot!

OT impedance/power questions(by Mike Knauf)

Wed, 17 Mar 2010 22:54:34 -0400

I read something I found a bit disturbing the other day and I was looking to get some others insight on it. "Running a lower impedance can make a tube amp produce more power but can contribute to premature tube wear and a harsher tone" Now my thought has always been that with a tube amp there will be an optimal point where you will get the ideal power transfer that comes from impedance matching... i.e. for a SE amp: Zp = Vp^2/Pmax Well this is ideal there also the load line approach which also yields one maximum power impdeance for any give plate and screen voltage, going higher or lower should lower the power if I am seeing this correctly. Now power aside, I was also under the assumption that a lower primary load was safer that a higher one, maybe not for the tube itself but for the transformer. As far as the tonal aspect I could also see where too low a load would sound very poor but the same with too high a primary load... Also is my assumption correct that a higher primary load will minimize 2nd harmonic distortion in a pentode?