AX84 BBS

Amp Parts and Kits

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

designing small amp(by Pete H)

Thu, 23 May 2013 16:52:38 -0400

Hey guys. I've had fun with my HO and SEL, but I figure it's time to leave the comfort of the nest and have some fun trying to design a basic amp. Hopefully I'll learn something, at least! I thought I'd begin by using a spare 269EX transformer and a 6V6, single-ended. With some judicious borrowing (the power supply from the Uber and one of Merlin's effects loops), I came up with this. [link] I'd love some feedback/critique. For example, the voltage divider before the cathode follower doesn't feel right, thoughts? This circuit is obviously fairly simple, but I'm hoping by fumbling through some designs, I'll get a better grasp on what's going on. If it makes sense, I'll try building it and see what it sounds like. Thanks, Pete

P1eX clean for jazz(by Michael McCarthy)

Thu, 23 May 2013 16:45:08 -0400

I have in mind building a clean p1eX for jazz. It doesn't have to be perfectly clean when dimed, but I would like it to be clean at least through the first half of the gain control on the first stage. I'm thinking of the following changes from a standard p1eX: 1. Allen TO11C output transformer, since the Doberman is not available. 2. Moving the tone stack to between the first two stages. 3. Adding a 0.022uF coupling cap following the second stage, before the master volume control. 4. Using the Merlin bone ray tone stack. 5. Placing the tone stack right between the first stage coupling cap, and the R21 gain attenuator. 6. Using a 5751 instead of a 12AX7. Here is a schematic: www.mccarthystringedinstruments.com/file_warehouse/20130521_BAS.pdf I have a few questions: There are some positions of the bone ray controls that have no capacitor in line, or no resistor in line, so I assume that the stack has to go right where I described it, and not obviate anything there. Are both of those assumptions correct? I do need another coupling cap after the second stage, right? Will this design, with the tone stack moved, and a 5751 instead of a 12AX7 have plenty of clean headroom? Is there anything else I might consider to go in a clean direction? I'm not interested in much distortion; maybe a little bluesy crunch, but that's about it. Sorry about that, Zaphod, et. al. I would really appreciate any comments from the fine people here. Thank you very much!

Accidental Bass Amp haha(by jlaustill)

Thu, 23 May 2013 15:31:06 -0400

So long story short, about 2 years ago I built an amp using the Simple Preamp schematic and the 20W SE schematic. The only changes I made were that I used an 5AR4 rectifier instead of diodes and I used a 6L6 instead of the KT88. I'm pretty sure other than that it's those schematics, although I can't honestly remember, it's been 2 years... So another long story short, it got plugged into a 1x15 bass cab with a Fender P-Bass as a backup last resort it might work kinda thing and ended up blowing us away with how dang good it sounds! The funny part is that it had ended up in my shed because it never made a very good guitar amp at all. It always had a great clean tone, but didn't distort nicely AT ALL. So now that I know how good it works as a bass amp, I'm going to toss a KT88 in it instead of the 6L6 and see if I can't squeeze 1 more dB out of it. It's putting out right at 100 to 101dB as is, which is perfect stage volume, but breaks up a little turned all the way up. Hopefully the KT88 will give us that hint more of clean room. Now, the reason for this thread is, I'm wondering what else y'all would change if you were to build a bass amp this way??? I can't imagine it sounding better, but who knows, maybe it could? One thing is for sure, it's getting a painted case to match a vintage Fender 1x15 cab I picked up yesterday for 100 bucks and will permanently be a bass amp from now on...

Question on paralleling more power tubes(by Pinball Wizard)

Thu, 23 May 2013 15:00:05 -0400

Hello all, I saw a bit of good projects here on ax 84 and i think i will build a P1. now i would like to ask a pair of questions: 1 ) i have a PT with output 200 230 and 0 how i can match at the best results the project wich indicates a 214 0 214 (214 if i am not wrong) (i mean 0 for ground .. i think you used that kind of PT for eventually use a half wave rectifier and that would be fine but i have that PT and not plannin to use valve rectifier). 2 ) can you give me some advice about paralleling 2 (or more) el 84 supposing i have the right OT rating and impedance.. i have seen some schematic here but i want it to be single ended .. so please in short what i have to change to the original schematic to get for example 4 el 84 in SE working (dont mind the power but eventually the tone).. and moreover if you know that can you say wich is the rule for calculating that i mean supposing i have 8 power tube tu use and want to try to buld sich thing also for fun.. can you suggest some tips? (i also have an El 34 Se amp on the bench with similar intentions). Thanks all and hope this is a new question. Cheers, Paolo.

comanchero question(by Seth Leigh)

Thu, 23 May 2013 11:33:03 -0400

I've just started my long-delayed Comanchero project. I made the turret board, and ceremoniously soldered on the first two components, a pair of 4007 diodes that I had left over from my SEL project. I'm confused about some things. I understood from my SEL build that a standby switch was necessary to prevent some potential damage to the circuit from voltages hitting the tubes before the heaters were warmed up. The Comanchero hasn't got a standby switch. Why is that? I'm going to take a SWAG and guess that it has to do with the difference between a single-ended output tube drawing current all the time, while the push-pull isn't drawing that kind of current until it's played. My SEL used four 4007 diodes for the rectifier, with two of them coming up from ground, and the other two connected to the two power wires coming from the transformer. The Comanchero only has two 4007 diodes coming from the transformer wires, with nothing attached to ground. What's the reason for this difference in the rectifier? I'm going to be googling for this topic, but thought I'd ask here, since the difference exists between these two designs.

Pure Tube Power Amp(by ParadoxGuitarist)

Thu, 23 May 2013 11:31:16 -0400

I've been thinking about getting a half stack for a while now, but most of the heads that I would want are way too expensive. I have a Deville 212 and for most things it's plenty loud (if not too loud at 60 watts). The way my rig is set up is that I have no real need for preamps/eqs gain since I use a multi-effects pedal (either a POD XT or a zoom G9.2tt) and I'm generally happy with my tone/effects/settings, but I still love the sound of tube driven speakers/cabs. It adds something that you just don't get (even with the tubes on the zoom pedal) So essitially I would be spending 700+ for a tube head that I would probably just use the "Power Amp" input on and forgo the rest of the cool possibilities. My thought was to create an all around Tube head that could be paired with multiple cabinets but have no preamp since I'll already be feeding it a line signal from my pedals. My hope would be to have a couple of sets of tubes which could be activated with different switches. (15-30-60) so I could use the same head with a 2x10 or a full stack. Biases for the tubes would be necessary as well since there's no preamps to I've poked around the site a little but I haven't found anything like this online. But... maybe one of you guys could point me in the right direction. =) If nothing like this exists, that's fine but maybe someone could point me in the direction of some reading for power tubes bias so I can design it myself. Whatever I end up doing myself I'll be sure to open source and share here. Thanks guys!

Filter Caps in Tweed Circuits(by Bill Ryan)

Thu, 23 May 2013 02:48:27 -0400

From time to time, I see articles or posts suggesting that tweed filter caps are generally under valued. I've seen suggestions for upping the values in a 5C1 to 100uf at primary and 40uf at secondary filter. Any thoughts out there regarding pros and cons to this approach?

18W build(by David Staepelaere)

Wed, 22 May 2013 23:02:46 -0400

I finally got around to finishing an 18W build I started a while ago, so I thought I'd share some photos. [link] I got stalled on the project after I'd finished the chassis. I was playing it through a 2x12 cabinet loaded with a G12H 30W 70th Anniversary and a G12 Vintage 30, and I really didn't care for the tone much, either with single coils or HB, so I put it aside. Eventually I got around to building a cabinet for it -- as much just to "get it done" and have a safe place to store the chassis as anything. I paired it with an Eminence Wizard and decided I liked the sound much better. A tele and very moderate breakup sounded pretty good to me, higher volume settings with humbuckers also sounded pretty decent. I almost didn't want to take it apart to put on the tolex. I know speaker/cab choice is a major factor in how an amp sounds, but I guess I just needed a little reminder. Regards, David

Space alien sound, no guitar sound(by Larry)

Wed, 22 May 2013 21:19:35 -0400

Powered up my HO and am getting a weird space ship-death-ray sound. No guitar sound, no difference with cable only plugged into input. When I chopstick I get nothing until I press down on R7 positive end and it's connecting wire to pin 9 of the EL84. Then the sound stops and comes back a second later. I should add that I don't know what I'm doing. I may also have a different value than spec for R3 and R7. The bands are hard to read and my meter is saying 37.11 Mohms...any wisdom from you gurus?

Hammond PT and OTs for sale or trade(by plotch)

Wed, 22 May 2013 20:35:43 -0400

I have one used PT and two used OTs to sell or trade. I need a PT for a P1 extreme build, and two smaller single-ended OTs suitable for 5F1, P1, P1EX or similar. 1) Hammond 372BX single-ended PT. Used, but with low hours and enough lead to attach to tag strips. This is a universal transformer which can be set up for any input voltage. 2) Hammond ESE used 3) Hammond ESE used Thanks! -p

5F1 Champ Parts List?(by Matt D)

Wed, 22 May 2013 14:35:56 -0400

Hi All, im looking at a first build project - a 5F1 champ seems about a good starting place im thinking. im sure there is a list on here somewhere, but does anyone have a parts list and a 'colour by numbers' layout available? id prefer to source parts myself as being in new Zealand shipping costs the earth from just about anywhere. im thinking either a champ or tweed deluxe build - ala the ones on tube depot's site, and if someone has a parts list and build guide available that would be great!! cheers, Matt - NZ

StJarvis's Guitar Build Thread (hopefully)(by stjarvis)

Wed, 22 May 2013 13:26:55 -0400

So I bought Benedetto's book on Archtops, and decided to try my hand at making a guitar from scratch (well from dimensioned lumber). I'll be building a semi hollow, well reserve actually building an archtop with bent sides for later. Drew up a plan in DraftSight: [link] Laminated so wood for the neck: [link] Clamped (Hard Ash, Paduak, Purple Heart, Rock Maple): [link] Cleaned it up on the tablesaw: [link] Routed / Milled truss rod channels on both sides: [link] [link] Separated the necks: [link] [link] Cutout the necks / Cleaned them up on the ROSS: [link] [link] Got a Flamed Koa headplate and Ziricote fingerboard from the UPS man: [link] Glued the headplate on one of them: [link] Started making a fret slotting jig: [link] More to come.

noise isolation, guitar or amp(by Seth Leigh)

Wed, 22 May 2013 13:06:56 -0400

I've noticed that in my mancave, with all my computers and whatnot, my amp and guitar combo is very, very noisy. At my parents' house, it's very quiet and I can really crank the volume much higher than I can in my cave. When I click on my tuning pedal, cutting the guitar output from the amp, the noise ceases, which leads me to believe this noise must be coming from the guitar and not the amp. Would that be correct? My guitar has two humbuckers in it. The control cavity is shielded with copper foil, the wire leads going to the humbuckers are shielded, etc.

Resistor values for power supply(by Pete H)

Wed, 22 May 2013 08:41:44 -0400

I've built the HO and SEL, and have thoroughly enjoyed tinkering with them. I definitely have made some mistakes along the way, but have learned a ton. I do have a question about the power supply and the resistor values in the RC filters - how were the values of R2, R3, and R4 selected? There may be a thread about this, but I haven't found anything yet. They look to be the same for the SEL and the HO, but are different in the Ubergain, even though the SEL uses a KT88 like the Ubergain does. Thoughts? Thanks, Pete

first time - 5f1(by Seth Crabtree)

Wed, 22 May 2013 00:17:11 -0400

I'm working on my first build, a 5f1 from Watts Tube Audio. I was hoping for some guiding hands, as well as general advice. I've got the board wired up, but I believe there are already mistakes, as well as perhaps a poor choice in that I've used cloth covered wire (because it's what I had...). I've heard one shouldn't use cloth covered wire in amps, but I don't know if this is a "no, really, don't" thing or just a popular preference. For brief background, I've done a decent bit of wiring, mostly in guitars, and I've been reading and studying on forums for a while (though unfortunately, not so much on this one (as most of it's still over my head). The Watts kit is pretty old school, and I've just the old Fender layout to go off of ( [link] Looks to me like there's no pics in these forums, so here are links to shots of the board on imageshack. If there's a better or more appropriate way to post pics, please, enlighten me. I'm hoping for some error checking, as well as comments about how well/poorly I'm doing so far. I feel like I'm about two steps shy of mediocre over all. Some of my soldering is decent, some not so much. The cloth wire is perhaps a concern. The big thing is the resistor to the right of the two black caps which on my layout is marked just "470." I believe I have the component wrong there. From looking at pics of other's boards I generally see one of those bigger square white things, not a little resistor. I'm assuming that I've done something wrong, but I also wonder if perhaps this Watts kit is just old school or something. In any event, there was no such component in the kit, though I certainly won't let that rule out the possibility that there should have been. Full board, front - [link] Half board, front - [link] Other half board, front - [link] Full board, back - [link] Lastly, a theoretical question. I considered omitting one of the inputs and replacing it with a standard switch (as opposed to the volume knob which doubles as the off/on). I just don't really need two inputs and I prefer the solidity of a real switch instead of a free moving knob (especially since I won't always have a speaker hooked up). Were I to do this would I simply omit one of the 68k resistors and proceed as normal otherwise? My many thanks for any and all assistance.

Help me name my amp.(by arjepsen)

Tue, 21 May 2013 23:22:09 -0400

Just about finished my latest amp. It's pretty much a 2xel-84 version of a matchless DC-30 - used schematics I found on trinityamps.com, plus a bit of mods from here, there and everywhere. I'm trying to build a nice hardwood (nyatoh) head cabinet for it, and want to put an ash front on it, with a name carved out, so that you can see the tubes inside. But I'm having trouble deciding on a name. I thought about DC-15 - but that's too much like the mathcless name - I'd like it to be a word/name. I thought about "Lightning" (one of the channels is basicly a lightning preamp), but it's a bit too long a name for the front, and again I'd like the name to be a bit more "mine", than just taking one from matchless. Thought about Fox-15, but realized I got that from the Brown Note website. Thought about lightning/fox/etc. in another language - like Latin. But "Vulpes" and Fulgur somehow sounded too weird. So.... any ideas / suggestions? Regards. Anders

decrease bass in a tweed 5e3(by Andyman)

Tue, 21 May 2013 20:17:45 -0400

I read a lot about the 5e3 deluxe and the excessive bass it has.. A lot of recommendations are too cut down the preamp couplers to 0.022�f from 0.1�f. But since the volume pots function a bit differently in the 5e3 than say a blackface deluxe the coupling cap value have to be high as you would loose too much bass when you turn down.. And having less bass when played at low volume clean and then more bass when playing loud and a bit overdriven does not seem like the obtimal setup. So I looked at similar amps like the 5d3 with the paraphase inverter and that one uses 0.05�f in both preamp and power stage. The two tweed tremoluxes have the same 5e3 preamp but uses 0.02�f couplers in the power stage. So if you wanted to cut bass with a 5e3 and keep the bass nice and fat when played low but in better control when played loud would be to lower the power stage couplers from 0.1�f to 0.022�f. Regards Anders

6sn7 power section picture(by sdp1234)

Tue, 21 May 2013 18:58:15 -0400

Does anyone have a picture or two showing how they connected the 5.6k resistors to the 6an7s on a studio october or 440? Im doing my own layout and im out of room. Didnt want the restors flying but it looked like they may be on the socket of cliffs layout.

lead 2 tone stack(by sleigher)

Tue, 21 May 2013 17:20:31 -0400

Has anyone else worked with the lead 2 and found the tone stack to be extremely bassy? I swapped the tone stack out for the jalapeno option and it dramatically reduced the bass so much that is light now. I am gonna go back thru and look at some of the pre amp sections to see what I can do but was just curious what others may have done or noticed around this.

My new builds have low output, Help!(by sixstringer)

Tue, 21 May 2013 16:38:23 -0400

Greetings, I have just completed 2 more of Dave Hunter's Two Stroke" amp design. I've built 3 of these previously, they all work great. These two new ones have about 20% of the volume of the others and sound slightly more distorted. I replaced the tube rectifier with a Solid State version, that is the only change from original design. I've built this amp with selectable tube/ SS rectifiers before so it know it's do-able. I've checked (and rechecked) all the usual stuff: correct value components, correct polarity, tubes, speakers, grounds, solder joints, and so on. The voltages throughout the amp are on par with the other working amps (about 30 volts higher on the B+ than the tube rectifier version, which is to be expected). The waveform looks the same from amp to amp and I have traced the signal all the way to the OT in both amps. I'm stumped. You thoughts and advise are most appreciated.

PSUD2 and Firefly power supply circuit(by cfwahl)

Tue, 21 May 2013 09:46:31 -0400

I recently created a model of the Firefly power supply using Duncan Amps PSUD program. The results were not what I expected, so I'm wondering if any folks here who have experience with both the Firefly and PSUD could explain why. Here's a screenshot of the program's window: [link] I used an actual Hammond 269EX transformer, measuring resistances of primary and secondary, and unloaded voltage when powered, to create the source. Full wave rectification with 1N4007 diodes, capacitor values from F&T for the 47u, and I inserted loads based on the average current draw of 12AX7 (2 x 1.2mA) and 12AU7 (2 x 20mA) tubes. As may be seen, I calculated for 15 seconds beginning 11 seconds -- a "steady-state" condition where nothing was changing. What I come up with is correct for the B+1 node (265V), but voltages are low for the others: down to 103V for B+3, as opposed to 210V on the Firefly rev 3 schematic. Can anyone help explain why that is, or what I did wrong? Thanks, CW

Quieting down a 6SJ7(by Stevo)

Tue, 21 May 2013 06:12:34 -0400

I was curious if anyone has any advice regarding quieting down a 6SJ7. The amp it is in has the following topology: parallel 6SL7 gain stage => tone stack and volume control => 6SJ7 => 6SN7 gain stage => 6SN7 cathodyne => 6V6 push pull output. Upon testing, I've pulled tubes, adjusted components, chopsticked and have determined a couple of things. Without the 6SJ7 in the circuit (ie. bypassed entirely - output of the volume control feeding the 6SN7 gain stage) the output of the amp is considerably diminished, but there is no hum. It is a nice, quiet amp. With the 6SJ7 (100k plate resistor and 2.2M screen resistor) there is significant hum. Just wondering if anyone has any tips on how to work with this, or if it might just be a condition of using such a tube (which would be a shame). Oh, and I've got a few other 6SJ7s. They all contribute this hum...

Inductance in mock poweramp stage?(by JHarris)

Mon, 20 May 2013 23:03:52 -0400

I've been toying with the idea of an amp build that has an option for an adjustable (and low) power SS output stage, driven by a non-power stage designed to create distortion. I'm aware of the McTube but understand it to be a sound more like a fuzz box than an overdriven poweramp. I actually like the sound in the Lead 2 preamp clips that I've heard but my understanding is that getting an accurate reproduction of the kind of sound you'd hear from an overdriven power amp using a preamp stage is limited by a few factors... 1. Different tubes. The 12AU7 sounds good in the Firefly and the Lead 2 so that's a good option to design around. For a real tetrode/pentode output stage sound, the 6K6 is the same kind of tube with power levels better suited for a non-power stage than a 6V6 or larger. 2. The interaction between a tube and OPT, and then the OPT and speaker, is not the same as a simple resistor which is what typical preamp stages use. The inductances are going to change frequency response, but additionally offset changes and amounts of voltage and current. I'm not sure if there's been much effort put towards a low-power simulation of the second set of aspects of a tube poweramp. I have a hard time wrapping my head around how the numbers will stack up because my understanding of series/parallel circuits does not extend to components on the other side of a transformer. That said, data is available on the inductance of some speakers as well as that of output transformers so it should be possible to get close to an accurate model of what's going on in an output stage. Has anybody messed around with the idea of putting an inductor in series, or in place of, the load of a preamp stage and found how it affected the sound? Could anybody give me an answer to whether the amplitude of sound coming out of a speaker at a given frequency depends more on current, or instant power? The latter is basically referring to what extent power factor may have on the apparent sound levels and frequency response, as opposed to a simple signal you may draw off of a given amplification stage.

6 x EL34 / 4 x KT88(by DaveW)

Mon, 20 May 2013 16:46:24 -0400

I am building a HIWATT type amp using a similar preamp to the HW 'Jimi Page' version. I have an Sound City 120 PA chassis which I am using as a donor for the chassis and iron. This used 6 x EL34 valves. I have read that the iron would be OK if I used 4 x KT88 valves instead of the 6x EL34. I have a few pairs of KT88s but not a matched sextet of EL34s. I have searched the web and come up with an OT that supports 6 x EL34s (2.2k impedance) and also one that supports 4 x KT88 OT (1.9K impedance) so I think it looks reasonable. I know I will have less B+ than the KT88 can run at but I don't mind a little less power. It would also have the advantage I could pull two of the KT88s and set the speaker impedance switch to half the cab impedance for even less power, which would be tricky with 6 x EL34s. Is this a reasonable substitution? Thanks Dave

Increase wattage(by agordon)

Mon, 20 May 2013 13:00:02 -0400

I built my first amp with the P1 preamp and P1-extreme power section (octal tube). Now a friend wants the same amp, but to increase it to about 50watts for the larger gigs he is playing. My first thought is that I would need to make it a PP amp rather than the SE as now. But, is that true? Can I increase to close to 50w with the SE design? Any advice is appreciated.