AX84 BBS Threads with new messages as of Mon, Oct 20th, 2014 @ 10:40:16 Amp Parts and KitsDoberman Music Products, LLC offers a variety of parts and kits Epiphone Valve Special plate voltage(by chee16) So I have done a lot of mods to my Epiphone Valve Special, essentially converting the preamp to as close to the Matchless Lightning as possible, eliminating the DSP and now trying to bias the EL84 properly. I used this tutorial for biasing (though it is for the Valve Junior) <a href=" " target="newwin1413816016">[link]</a> So using the method I have my dissipation at about 14watts, that is with a 270ohm/2w resistor from the cathode to ground, where the stock resistor is 220ohm. My cathode voltage is 11.75V, and my anode voltage is 339V which seems way to high. Using those numbers for the dissipation gives me just over 14watts. Too high. I measured my wall voltage and it was 122V. In the article the guy talks about upping R10 from 220ohm to 1kohm. That sound fine except the Valve special doesn't have an equivalent resistor. Here are the VJ schems <a href=" " target="newwin1413816016">[link]</a> Here is the schem of the Valve Special, I put in the values as they were really blurry <a href=" " target="newwin1413816016">[link]</a> Version 1 of the VJ doesn't have the R10 resistor either, so I am thinking I could safely add one into my circuit. Does anyone have any insight into this? I doubt specifically to this model amp as the VJ craze is pretty much gone, but hopefully someone can tell me if I am thinking correctly. It should bring the B1,2,3,4 voltages down correct? Looking the the VJ schems and comparing Version 1 and Version 2 it seems that when they added R10 (220ohm) it dropped the B1,2 and 3 voltages down. Thank you, I hope I was clear in my description. Mon, 20 Oct 2014 10:11:19 -0400 Anybody still using leaded solder?(by Kursad K) <a href=" " target="newwin1413816016">[link]</a> "No safe threshold for lead exposure has been discovered—that is, there is no known sufficiently small amount of lead that will not cause harm to the body." (quoted from the above) KursadMon, 20 Oct 2014 09:55:39 -0400 slow guitar build(by tedmich) getting a project going, found the (wing) wood in the road ~10 years ago in PDX just finished it up with Liberon's Finishing oil, 5 coats with only 5h between coats, then 3 coats Renaissance Wax <a href=" " target="newwin1413816016">[link]</a> <a href=" " target="newwin1413816016">[link]</a> <a href=" " target="newwin1413816016">[link]</a> here’s the 30” scale LMII Mad. Ebony fretboard, slotted to 3 octaves with maple filling slots 35/33/31 (and the sausage fingers which make this necessary!) <a href=" " target="newwin1413816016">[link]</a> heres how it will go together with Kahler 8 string bridge ($165) “blem” and the EMG 808 hole <a href=" " target="newwin1413816016">[link]</a> Sun, 19 Oct 2014 17:43:41 -0400 Anyone willing to build my PP reverb and give suggestions?(by Darren Porter) I was wondering if anyone would like to build my PP 12AT7 reverb and give their experienced insight into improvements in the circuit and share your layout ideas. This is my first attempt at a design and scratch-build. I think it sounds pretty good but I also think it could be better but I really have no clue how to improve it. It is a very simple design, two tubes. If you have a Firefly it would be extremely easy to convert it over.Sun, 19 Oct 2014 15:49:57 -0400 1-5 Watt Pentode tubes for SE project(by Alva Goldbook) I keep thinking about building a low watt SE amp, for a high gain British type sound. I'd like to build this guy for *cheap*, so a low watt amp that won't draw too much current would be appealing. I'd like to get something that draws less current than a EL84 or a 6V6, so I don't have to lay down too much money on a power transformer. I've thought about using a 12AU7, but I've heard a lot of folks report that they don't like triode sound very much. So I'm thinking that maybe there's a more rare tube (that I'm currently not aware of) that will get the job done. Any suggestions?Sun, 19 Oct 2014 10:13:34 -0400 Looking for a project reusing these transformers(by Stack) I have an old ADA Microtube 100 that hasn't worked in years, I pulled the transformers and thought that they could be used in a standalone preamp project. I've looked at Bancika's blackbox, but I don't think this iron will support that. I already have an HO and a firefly which would seemingly be good projects but I've already been there. Here is the link to my drawing of the original supplys from the ADA <a href=" " target="newwin1413816016">[link]</a> the voltages got cut off my scan, they are: 170V B+ -12V Filament following the LM7912 I found an ADA xfmr from an MP-1 to get you a relative size of the transformer <a href=" " target="newwin1413816016">[link]</a> There is also a torriodal transformer of unknown rating, 22.5V - 0 - 22.5V - 0 which I haven't figured out what to do with either... All ideas welcome.. Thanks in advance. -TroySat, 18 Oct 2014 18:31:09 -0400 advice on building and designing amps for a living(by CChurchill) I fell into this rabbit hole of amp, guitar, and effects building about five or six years ago. To make a long story short, building tube amps quickly became as much of an passion as playing guitar. I've been reading everything I can get my hands on regarding the subject. I want so badly to build and design amps for a living, and the thought of doing anything else blows(quite frankly). It can be frustrating learning on my own, but there aren't many job postings for Tube amp apprentices. I'm looking for any advice I can get. Sat, 18 Oct 2014 13:24:39 -0400 Phase Inverter Buzzed(by Dire Wolf) I am getting a loud buzzing from my PI even with the preamp tubes out. I have used a wooden pencil to poke and prod and found as I tap on the grid connection wire for one side of the PI I can hear the tapping in the output. The preamp works and can be heard however this buzzing is dominate. With a lightbulb limiter the sound is still present, not as loud. I have built the circuit before and had no issues. The connection in question is pin 7 of the PI. Any thoughts. Here is the schematic. <a href="" target="newwin1413816016">[link]</a> Sat, 18 Oct 2014 02:54:11 -0400 11% off at Darren Porter) FYI... like the subject says... everything at (this is the same company as AES/ - just a different web front-end) is 11% off until October 31st. I don't quite understand that whole company... and one other one that eludes me at the moment are all the same store but just a different web front-end. Oh well, as long as they sell what I need and have good service that's all that matters I guess.Sat, 18 Oct 2014 00:57:38 -0400 Dr. Z, Mini Z Schematic(by Alanh) Anybody have a Dr. Z, Mini Z Schematic? ThanksThu, 16 Oct 2014 17:41:14 -0400 WGS ET-65 vs WGS Vet-30(by JeffW) I made a clip with the first half being the ET-65 and the second half being the Vet-30. Both in my slant front with a e609 mic. Thought it was kind of interesting. <a href="" target="newwin1413816016">[link]</a> Wed, 15 Oct 2014 18:42:17 -0400 50W PP standalone - OT wiring confusion and other questions(by EeroNiemela) I'd like to build the standalone 50W PP as my next project, and at the moment I'm a bit confused about the OT wiring. It says on the 50W PP schematic to use the 56k NFB resistor when using the rotary impedance selector (which I'd like to do). What confuses me is that the 56k value is for the 8 ohm hookup, but it is always connected to the GRN (4 ohm) wire on the 1650N OT. So why 56k and not 27k for the NFB resistor? Also I can't see how the 16 ohm position (pos 1) on the switch is supposed to work. According to the 1650N datasheet, the secondary windings are as follows: BLK-GRN (0-4 ohm) BLK/YEL-GRN/YEL-YEL (0-4-8 ohms) Now, the 16 ohm position seems to connect GRN to BLK/YEL and GRN/YEL to output jack tip. BLK is ground. So that would put two 4 ohm windings in series for a total of 8 ohms, not 16 ohms. What am I missing here? Also, how is the Hammond 1650N for this amp? I understand that the Hammond OTs are nothing specieal, and I'd like to go for something nicer. I could get an InMadOut (Italian brand) transfomer for the same money: <a href=" " target="newwin1413816016">[link]</a> It has a 4.4k primary instead of the 4.3k of the 1650N, but this would be close enough I imagine. Also as for the choke, I assume it's not a problem to substitute the Hammond 156L for a bigger one, such as the 159Q (7H, 150mA, 100R, 500V? And I assume I could increase C1 to 100uF for a punchier response? Thanks!Wed, 15 Oct 2014 03:44:49 -0400 5E3 project questions(by Audiosalvage) Hi all, I'm starting a conversion from a 1955 capehart push pull 6v6 amp to a 5e3 deluxe. It has a layout unlike your usual guitar amp. It's more square shaped with the PI between the 6V6s. Since it has all the pots already mounded and little or no AC hum when cranked, should I just gut the preamp and point to point the new components or start fresh with a more conventional fender layout? It is pretty tight to add a turret board. Another thing I'm concerned about is that it is not that loud even at full volume. Is this just an impedance issue because I'm feeding a guitar through it? ThanksTue, 14 Oct 2014 16:18:13 -0400 Building a tremolo into Fender Bassman(by JaapK) I’m using the circuit of the Fender Vibroverb to make a tube tremolo into a Bassman; see circuit: <a href=" " target="newwin1413816016">[link]</a> On my scope I get the right wave so the trem does work, but built into the Bassman there’s a very little tremolo effect. I suppose that is because the bias must be adjusted. The Vibroverb shows around -62V and the Bassman around -45V; both with about 440V for plates/screens. I did not dare to put the intensity pot all the way cause I’m afraid to fry the 6L6 tubes. Can you guys help me: what is the right and safe range for the bias voltage; to make the trem work well and keep the tubes alive. Is that around -62 V to -?? Volt with the intensity pot at max? And isn’t the amp biased way to cold with -62V? Thanx. Jaap Tue, 14 Oct 2014 11:49:03 -0400 Heater Center Tap(by JB Angelo) I've had my Route 66 clone for years now and it has always had a hum to it. I have tried everything and can never get it quiet. Until today.....I realized I added two 1 ohm resistor between the power tubes cathodes and ground to simplify reading the bias. But the center tap of my heater I grounded directly to the chassis. Now the original design didn't use these resistors. By adding them early on did I just elevate the power tube cathode above the heater ct, thus inducing hum. I never had them removed to see the difference. I am currently rebuilding it. all point to point with a cleaner layout and star grounding. So I can't test my theory until i'm done. Any ideas, thanksTue, 14 Oct 2014 10:54:06 -0400 AX*$ SEL KT88 for sale(by automap68) AX84 SEL with KT88 and the 2 stage pre amp Built 2 years ago. Finished as a project and just sat. Lots of pictures of my build on this site. Just happen to be cleaning out my closet. If anyone would like it let me know Please email me at If you search my name you will find the original build thread from 3 years ago with specs I tried to post a link to it but it won't let me Make an offer. Think i spent $400 in parts alone not to mention 2 months building it. Would let it go cheap <a href=" " target="newwin1413816016">[link]</a> <a href=" " target="newwin1413816016">[link]</a> Tue, 14 Oct 2014 09:31:34 -0400 Getting less negative feedback(by David Hodgkins) Looking at my Ecolette. Schematic here: <a href=" " target="newwin1413816016">[link]</a> This amp is super clean and bright. Even jumpered and dimed there is virtually NO breakup. I'm mostly fine with the cleaness, but this amp is super bright as well as lacking in overall volume. (Not that I truly NEED more) But I just feel that there should be more. In order to get a warm sound the presence needs to be all the way down and the treble on about 2. I just think that there's altogether too much NF. If this was a standard NF loop, I would just increase the resistor, but I can't really understand this topology. This is an early PC board amp, so I'm somewhat limited on my mods. If I lift C21 and R38 I get a lot more volume, but I loose my presence control (which I never use), but I'm just looking for a more educated and sensible mod. Any help is appreciated! Tue, 14 Oct 2014 02:58:41 -0400 Look what the cat dragged in(by Chris Hurley) Hey guys- I wanted to pop in and say "hello" since I've been away for a while, though I have enjoyed emailing some of you from time to time. The last few years had been somewhat rough due to family things but I'm mostly through all that now and I'm starting to get the bug to build again. I've been tinkering around with a few odd-end ideas here and there but haven't harvested any real fruit. I'm currently fiddling with ideas for how to control various things in an amp using a microcontroller. Switches and shunts are the easiest things to control but I'm not having much luck replacing a potentiometer with something I can control easily from a microcontroller. I tried to use a MOSFET as part of a variable resistor- it "worked" but distorted as the controlling voltage was dropped. Yuck. I could easily use some sort of switching device (LDRs, relays, etc...) to switch the wiper on a resistive ladder. That will work but it will take up a lot of space and a lot of controller lines. I bought a couple of digital potentiometers which appear to be resistive ladders with mosfet switches for the wiper. The biggest issue with these is that they will only tolerate 5v, so you can't just use them anywhere in the amp. I haven't tried them- they may sound bad too. Motorized pots aren't especially easy to come by. I could use a stepper and some sort of linkage to a regular pot, but thats going to be large and burn a lot of controller pins. Perhaps nothing beats the sound of a well designed single channel amp without any of this nonsense but its fun for me to think about and fiddle with. I hope everyone is doing well. -Chris Mon, 13 Oct 2014 08:12:27 -0400 ECL82 push-pull with 22k primary?(by BJosephs) Hi All, I've been working on a small push pull amp using an ECC99. I get about 3 watts with a 22k primary and 270v B+. It works but I don't really like how the ECC99 sounds when over driven. I swapped in 12AU7, 12BH7 tubes and tried various combinations of fixed and cathode bias. I think I'm just not crazy about triode output stages. I'm looking for options to modify the amp without increasing size or output power, and continue using the same OT - but switch to a pentode. I'd prefer something that I can get matched/current production of so I'm looking at ECL82 which can do 10 watts at 250vDC with a 10k primary. My OT is rated at 5W but it's bigger than the Hammond 125D (10W) so I think it can handle a little more than 5W... anyone think that running the ECL82 at 2X load impedacne would be a good direction to achieve those goals? I'm going to pull down the characteristics and try a load line but I like to test the waters for experienced opinions too. Thanks, Brian Sun, 12 Oct 2014 14:30:19 -0400 Design "best of two worlds" amp...(by Darren Porter) Well after three successful builds I think what I want to do next is build my "dream amp" for on-stage use. It will be true two-channel (maybe three), foot-switchable and on-board reverb/effects loop. For channel 1, I would like the fantastic clean sound of my Simple Preamp mated with the 20W PP amp from here with its own TMB FMV tonestack. For channel 2, I would really like the 18-watt Lite IIb from with just the single tone knob. For channel 3, if I did it, I would probably want the EF86 channel of my Trinity TC15 (matchless/vox) with the contour control. Problem is, the amp I like for channel 1 is 6V6-powered with NFB loop, the channels 2&3 are EL84-powered w/no NFB loop. Any ideas? Would I like the simple pre's clean stage driving EF86's or the 18watt driven by 6V6's? Sun, 12 Oct 2014 12:47:37 -0400 Cool Cover(by Douche Baggins) Cool Hendrix cover by this guy: <a href="" target="newwin1413816016">[link]</a> Sat, 11 Oct 2014 17:04:45 -0400 long tail PI as power amp(by JaapK) I found this interesting info and just have been testing this: <a href=" " target="newwin1413816016">[link]</a> I was hoping to get a 'stronger' sound using tubes like 6L6 or 6V6 as compared to for example 26A7-GT which I have been testing a lot. But after testing my conclusion is that this set up does not sound better or worse than a power amp with a 26A7 GT or a DLL21. Just thought I share this and of course it's just my experience. I'm still trying and trying to get the best low power, low voltage amp ;) Jaap Sat, 11 Oct 2014 09:34:53 -0400 noise(by Tim B) Hi, been away for a while playing. I've been using my P1x at church and am now getting a lot of 60hz noise. It was running almost completely silent until about a month ago. There is bad lighting (noisy) and noisy power at the church but something has changed. I plugged in my AC4 and it was pretty quiet. I'm going to give it a complete check soon but any ideas for a good starting point? I'm running a KT77 power tube and a tung sol 12ax7 for tubes. It sounds great but the noise is bad, especially when I plug in a single coil guitar. It will sometimes go away for a while and come back randomly. Also I was considering adding a line out to go to the sound system. Anyone have a good schematic for one? Thanks, TimFri, 10 Oct 2014 19:05:27 -0400 P1 eXtreme transformer question(by aeronaut) Greetings, Has anyone played around with other transformers for the P1 eXtreme? Thinking of doing it for a first build, and it looks like one can get an Edcor CXPP30-MS-5K for about the same price as the Hammond 125ESE output transformer. The Edcor is rated at 30W, 20 Hz to 20 kHz, and has a 5k primary and 4, 8, and 16 ohm outputs. Seems like a lot more iron for the money, and rated to handle the bigger tubes the P1 eXtreme can take (perhaps a little shy for the KT88, but much closer than the Hammond's 15 W). Might be more than one needs, but for the same price, seems like a no brainer. Any concerns or potential problems? Or is the 30 Watt push pull rating the same as a SE 15 Watt because in push pull it only conducts part of the time? Even so, the better frequency response is still an upgrade, albeit perhaps not a useful one. Can't link it, but go to, menu bar class X, item push-pull. Seems to be way better value than the hammond tranny. Regards, Martin Thu, 09 Oct 2014 15:48:11 -0400 Bridge Rectifier + bias(by tooltime) Will this work? My PT has a single wire bias tap within the HV secondary tap, but as it turns out I cannot do this bridge configuration with the CT elevated, and get any negative voltage off that tap. So, I was wondering if I can use one of the legs of the secondary to create a bias voltage, as well as feeding the bridge. Will this work or will it short out the PT? <a href=" " target="newwin1413816016">[link]</a> Thu, 09 Oct 2014 11:28:45 -0400