AX84 BBS Recent Posts as of Mon, Oct 20th, 2014 @ 06:55:29 Amp Parts and KitsDoberman Music Products, LLC offers a variety of parts and kits RE: Epiphone Valve Special plate voltage(by chee16) Side note, I'm picking up a Valve Junior today if all goes as planned. It's brand new, from my local shop who I have dealt with for 20+ years. Plan is try out the Fender type mods on it. So a parts order will be happening soon anyways. Good timing really, haha.Mon, 20 Oct 2014 06:12:38 -0400 RE: Epiphone Valve Special plate voltage(by chee16) Just checked my screen voltage, 320V. So the drop across that 100ohm resistor is 6V. I found this about the screen grid resistor for the Valve Junior ( I know, it's a different amp, but the voltages are similar.....): "If you're using the stock VJr OT, a 4.7k/3w in R12 plus a 1K/1w screen grid safety resistor to pin 9 is good for getting your screen voltage back up into the 295v range. If you're using a Hammond 125xSE OT, a 2.2k/3w in R12 is a good choice. The 1k/1w screen grid safety resistor will help stabilize the voltage, and resistor rated for 1w will sacrifice itself to save the amp in case of a thermal runaway. At any rate, it's best to keep the screen grid (pin 9) below 300vDC for best results and long life." Considering my screen voltage is 320V this might apply? Sorry for all the questions. I am trying to learn as much as possible, so making things make sense is the key. I don't want to just read a tutorial and go through the steps, I would prefer understanding what is going on. Baby steps though. Mon, 20 Oct 2014 06:03:33 -0400 RE: Epiphone Valve Special plate voltage(by chee16) Thank you! I am going to check my screen current. There is a 100ohm/3W screen resistor already, unlike the original VJ that apparently didn't have one?Mon, 20 Oct 2014 04:53:56 -0400 RE: Epiphone Valve Special plate voltage(by RickTown) I think if anything, you might want to add a screen resistor first. That will drop your plate current without changing your bias resistor. There is also screen current on the cathode so you need to subtract that out before figuring your plate dissipation. From what you've posted, it looks like you've got about 5mA of screen current that you'll need to subtract from your total cathode current. That won't neccecarily kill your screen but a smallish screen resistor might help. Re figure your plate dissipation minus screen current and see where it ends up. Sun, 19 Oct 2014 19:08:02 -0400 RE: slow guitar build(by tedmich) <div class="quoteblock" >On 10/19/2014 @ 10:17, RickTown wrote : I can't believe you cut that groove by hand. At least I'm assuming that you did. I would have freaked out and failed miserably. Interesting idea too. Have you seen it done elsewhere or just a unique idea? I'd love to try it out. </div> it looked pretty bad after the burr, but this cleaned it up really well: <a href=" " target="newwin1413802533">[link]</a> Porter Cable makes (made?) one of these as wellSun, 19 Oct 2014 17:43:41 -0400 RE: slow guitar build(by tedmich) it was an oddball idea I had, I've never seen it before. I've played long enough to have oddball ideas about many things on my guitar! Once you conform to the instrument for 30 years you begin to think about how you could change it to fit you better, kind of like Roths Sky Guitar, although he's several orders of magnitude better than I. I pressed the 33 Jescar SS frets today! <a href=" " target="newwin1413802533">[link]</a> <a href=" " target="newwin1413802533">[link]</a> used a HF 1 ton arbor press and a maple /ipe caul I inlayed two N45 magnets into so it would stay put on pressSun, 19 Oct 2014 17:38:28 -0400 RE: Epiphone Valve Special plate voltage(by chee16) Did some checking today: V1-Pin1 & Pin6 = 160V V2-Pin1 = 184V V2-Pin6 = 286V V3-Pin3 = 11.42V V3-Pin7 = 350V B+ Rail: (I'm going to call the position farthest left B1 and so on) B1 (to output transformer) = 368V B2 (to screens) = 326V B3 (to V2) = 286V B4 (to V1) = 274V So then: I=V/R =11.75V/330ohm =.0356A or 35.6mA P=V x I =339V x .0356A = 12.07 watts So I should be able to get things right if I use a 330ohm/2W for the EL84 cathode resistor? Everything I have read about the Valve Junior talks about a range between 220ohm and 270ohm, nothing above, but it IS a different amp.Sun, 19 Oct 2014 17:31:39 -0400 RE: Anyone willing to build my PP reverb and give suggestions?(by Stack) Here's my initial sketches of what I think could happen with only 2 tubes. First off I'm using more of the Firefly arrangement with the 12AU7 as the self-split and keeping the 12AX7 as pre and recovery. One major change is where the Dry signal is taken from... In the 6G15 et al, the Dry signal is passed through a cathode follower. With only 2 tubes in play, that isn't possible aas-far-as I can figure. I've also modified the B+ supply slightly, shifting the voltages down the chain and removing B+3. The last big change is to the tone circuit(s). I stole a page from Cliff Chappell's Comanchero and hung a bass cut and treble cut off circuit as to not attenuate the pre & recovery stages too much. Also, just for fun I added a footswitched mute/bypass relay. PSU <a href=" " target="newwin1413802533">[link]</a> Reverb <a href=" " target="newwin1413802533">[link]</a> This is my first impression based on your design and the 6G15 - hopefully I've implemented Merlin's LED's correctly. I'm trying to maximize the parts that are there w/o too much rework. If you see something that is totally wrong, let me know! (preferably before I buy parts) NOTE: Values not optimized, probably some duplicate part references too. Sun, 19 Oct 2014 15:49:57 -0400 Anybody still using leaded solder?(by Kursad K) <a href=" " target="newwin1413802533">[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) KursadSun, 19 Oct 2014 12:32:11 -0400 RE: slow guitar build(by RickTown) I can't believe you cut that groove by hand. At least I'm assuming that you did. I would have freaked out and failed miserably. Interesting idea too. Have you seen it done elsewhere or just a unique idea? I'd love to try it out. Sun, 19 Oct 2014 10:17:32 -0400 RE: 1-5 Watt Pentode tubes for SE project(by PhilS) 6005 or more commonly 6AQ5 is a 7 pin tube. Sockets are easy enough to get. 6AQ5 is fully equivalent to 6V6, except that you shouldn't expect it to stand up to the 300+V range that many amps supply for 6V6. It draws the same amount of current. If you want something that really just "sips" current, both on heaters and plates, take a good look at EL95. Heaters only nee 200mA. Plate plus screen needs 28.5mA @ 250V. If this is a single ended amp, with one preamp tube, you can get by with a much smaller power transformer. For an output transformer, you'll need a 10K primary. Find a 5K primary with multiple secondary taps and just use those secondaries as if they are rated at double the spec; IOW use the 4 tap as 8 and the 8 tap as 16. You can find these on eBay for cheap. Buy a few.Sun, 19 Oct 2014 10:13:34 -0400 RE: slow guitar build(by tedmich) I gave up on putting tiny pickups under 1st and 12th frets, I can always make another neck and I gotta play this thing soon... <a href=" " target="newwin1413802533">[link]</a> glued 33 fret fretboard down on neck, will rework peghead and install tuners soon, then press frets <a href=" " target="newwin1413802533">[link]</a> <a href=" " target="newwin1413802533">[link]</a> The neck is sooo wide I realized I am seldom if ever going to "palm it" and I play lately with my guitar (or 6 string bass) pretty high and vertical so I have opted for a neck which lends itself to "classical hand position" and to get added purchase I have ground a softly curved groove for my thumb down the middle of the neck back. Was nerve wracking to take huge carbide carving burr to smooth D shaped neck back: <a href=" " target="newwin1413802533">[link]</a> these leave wood deeply grooved and can burn hard maple if rpm too high, finished it up with odd dremel profile sander I've had for years, and it looks pretty nice now <a href=" " target="newwin1413802533">[link]</a> Sun, 19 Oct 2014 07:51:42 -0400 RE: 1-5 Watt Pentode tubes for SE project(by Alva Goldbook) Would you have to use a 7 pin socket for a 6005 or could you use a standard 9 pin socket? My only concern is the availability of parts for such a build.Sun, 19 Oct 2014 04:46:21 -0400 RE: Epiphone Valve Special plate voltage(by steve25) Go find the Weber bias cal pages as that's what I use to double check myself !Sun, 19 Oct 2014 03:43:36 -0400 RE: 1-5 Watt Pentode tubes for SE project(by steve25) A 7 pin 6005 is a nice little 4.5 watt tube and there are still thousands of them around for a song!Sun, 19 Oct 2014 03:38:25 -0400 RE: 1-5 Watt Pentode tubes for SE project(by trobbins) This link may help: <a href="" target="newwin1413802533">[link]</a> Sat, 18 Oct 2014 20:48:12 -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 RE: Looking for a project reusing these transformers(by Stephen Keller) <div class="quoteblock" >On 10/18/2014 @ 17:39, Stack wrote : Thanks again for the ideas. </div> You are welcome. I think "rememberer of good ideas" is one of my unofficial titles around here. Heaven knows they don't keep me around for my prodigious build output. StphSat, 18 Oct 2014 18:31:09 -0400 RE: Looking for a project reusing these transformers(by Stack) Stephen, Thanks for this link, the info here is great and Merlin's Trem/Vibe sounds very nice! The information I've read so far at is absolutely amazing - I will save this to my bookmarks. For the time being, I'm going to work from Darren's reverb design. I feel that this is a better opportunity to optimize a design, rather than mearly copying one. For the torroid xfmr I have , I'm thinking maybe a pedal board PSU with a few filtered and stabalized voltage taps..We'll see. Thanks again for the ideas. -TroySat, 18 Oct 2014 17:39:45 -0400 RE: Epiphone Valve Special plate voltage(by chee16) Oh I know! That is why I am asking on here. BTW, before I changed the cathode resistor from 220ohm to 270ohm it was more in the 16watt range for dissipation. Which can't be good. I think my next step is to pull the chassis again, figure out what goes to where and then measure voltages to get a better idea of what the other voltages are at. I'm guessing that adding a 220ohm resistor where R10 is on the VJ schem will bring down all the voltages? Which depending on the current readings might mean I will need to lower the other resistors. Yes, I am new to this and could be way off track. Thank you for any help with this. CheersSat, 18 Oct 2014 15:21:48 -0400 RE: Epiphone Valve Special plate voltage(by steve25) A EL84 is not a 14 watt tube, it's a 12 watt tube, and let me add that I would only bias it for 11 watts as the added ware and tare of 100 % makes for no added volume !Sat, 18 Oct 2014 14:17:55 -0400 RE: advice on building and designing amps for a living(by Kursad K) Feasibility of what you want to do depends on the local market. For example in Turkey I would never attempt to found a company which builds guitar amps, because most people would prefer the cheapest one with the most features money could buy. That means zero luck for any such attempt. In Dubai, you could cover your amp with gold and probably they would buy it without even listening to how it sounds. In US probably you could find a few customers who would appreciate the durability of a hand built amp with high quality components. That rests on the assumption of availability of skilled amp repairman. If they had not existed, you could not have an argument about durability or quality, nobody would care. Even in that case, unless you are Mr.Dumble, I guess it would be a difficult business, and I bet other people you mention have day-time jobs and that they only build amps at weekends. KursadSat, 18 Oct 2014 13:24:39 -0400 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="newwin1413802533">[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="newwin1413802533">[link]</a> Here is the schem of the Valve Special, I put in the values as they were really blurry <a href=" " target="newwin1413802533">[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 06:12:38 -0400 RE: Phase Inverter Buzzed; to twist or not(by steve25) Where is your mv located as its not on the schematic link you have in your very first post? Did you build the amp with a star grounding system and are you using separate filters for each power supply node?Sat, 18 Oct 2014 02:54:11 -0400 RE: 11% off at Stack) CE Distribution is the otherSat, 18 Oct 2014 00:57:38 -0400