AX84 BBS Recent Posts as of Sun, Apr 20th, 2014 @ 23:00:17 http://ax84.com Amp Parts and KitsDoberman Music Products, LLC offers a variety of parts and kitshttp://shop.dobermanamps.com Existing PT good enough?(by Dustin LeBlanc) Hey everyone, I am considering transforming my Blackheart Little Giant into a Comanchero. I am trying to do some cost estimating on the project to ball park what it will take monetarily before I decide to put the amp under the knife. I know that I will need a new OT along with other parts, I am hoping to reuse as much as I can from this combo. The speaker, cab, chassis, existing tubes, and as much other stuff as I can keep are coming along for the ride. The biggest items on the purchase list are transformers. I am trying to get specs on the existing PT and I pulled the chassis and here are the numbers: 0-100V-120V-240C <- Input/primary voltages I think? 5V-0 6.3V-0 275V-0-275V - secondary/ output voltages? I dont see amperage listed at all and that seems to be my main concern. The comanchero calls for 220-0-220@125mA / 3.15@4a Without being able to see the amperage on the PT, how do I know if I can reuse it? I assume it can be tested in some manner, though I dont know if I have the tools yet to do so. Any pointers on this? If I can reuse this one, it would save a lot on the project. I have heard that these amps came with decent iron and the specs on the PT seem to indicate that but I dont want to misjudge the requirements. I obviously have a lot to learn still, my only projects thus far have been some mods to this amp, building a boost pedal and modifying an OD pedal. I am eyeballing the Camanchero because I want a PP amp, not SE (the blackheart seems to be a darn fine SE amp as is). I am looking for something with the tight responsiveness of a PP amp as it seems small SE amps are too spongy/muddy for me. Future plans for the amp could include an effects loop and/or reverb down the road if that matters at all. Thanks!Sun, 20 Apr 2014 21:08:49 -0400 http://ax84.com/bbs/dm.php?id=484219 RE: October Bright Volume Noise(by John Bgron) When I test the resistor on the input jack with my DMM the noise stops completely. Tried replacing the resistor but the noise still persists.Sun, 20 Apr 2014 18:49:49 -0400 http://ax84.com/bbs/dm.php?id=484218 RE: Stand alone reverb!! Love this thing!!(by Zambo) yeah, I see it on the duncan site and it doesnt make a lot of sense to me so i always put in a screen resistor to make it lower than the plate but it seems like that was common practice back in the day. waiting for the education from someone who knows! If I can help with schematic or layout let me know.Sun, 20 Apr 2014 13:34:33 -0400 http://ax84.com/bbs/dm.php?id=484217 RE: Stand alone reverb!! Love this thing!!(by haiku88) Sounds great! I have a Boss/Fender reverb pedal and like it a lot but want the real thing and am going to see if I can build something similar to yours with parts from various Hammond organs. So far as the screen voltage being higher than the plate I got the same thing on a 6V6 SE amp I built recently (Gibson GA-9 FWIW) and no problems so far...but was curious and did some reading, learned that is common on many Fender 6V6 amps.Sun, 20 Apr 2014 13:15:01 -0400 http://ax84.com/bbs/dm.php?id=484216 RE: Stand alone reverb!! Love this thing!!(by Zambo) I dont know, i saw that on the schematic and wondered the same thing. seems like a screen resistor would cure the problem but i dont know that it needs cured. F3nd3r did some weird stuff but it was usualy still in spec as far as guitar stuff is concerned.Sun, 20 Apr 2014 12:25:46 -0400 http://ax84.com/bbs/dm.php?id=484215 RE: Stand alone reverb!! Love this thing!!(by JaapK) sounds great indeed! I'm working on a version with a 6V6 and notice that the screen voltage of the 6V6 is around 5V above plate voltage. Can that do any harm to the tube? thanx JaapSun, 20 Apr 2014 08:10:35 -0400 http://ax84.com/bbs/dm.php?id=484214 Stand alone reverb!! Love this thing!!(by Zambo) <a href="https://www.youtube.com/watch?v=ABGlD4lLIzA " target="newwin1398049220">[link]</a> Just built this and love it! Never had one or tried one but im a believer. Used the standard schematic for the g15 but instead of the 6k6 power tube I used a 12at7 with 1k cathode bypassed with 22uf . seems to work just fine.Sun, 20 Apr 2014 13:34:33 -0400 http://ax84.com/bbs/dm.php?id=484213 RE: October Bright Volume Noise(by John Bgron) Thanks for the reply. There is fluctuating negative DC voltage in the millivolt range coming into the bright and dark volume pots, I'm not sure if that's acceptable. I should also add the noise increases with the dark volume pot too but not as much as with the bright volume pot. I tried replacing the bright volume pot too. The Vintage/Modern switch now makes an audible thud through the speaker and crackles as it's being flipped. I'm sure it never used to do that. Thanks again guys, John Sun, 20 Apr 2014 05:59:07 -0400 http://ax84.com/bbs/dm.php?id=484212 RE: October Bright Volume Noise(by steve25) Has C20 gone somewhat leaky, do you measure any dc voltage coming into that brite pot? Try cleaning V1s tube sockets with a old section of round wound guitar string that you can just get into the recivers , in other words does not spread them open to the point of taking the clamping force out of them. Before you do this be sure to drain the power supply By turning just the standby switch on for a minute.Sun, 20 Apr 2014 03:53:24 -0400 http://ax84.com/bbs/dm.php?id=484211 October Bright Volume Noise(by John Bgron) Hi guys, My October Club has developed an annoying noise/buzz which gets louder as I turn the Bright Volume pot. I've swapped all my preamp tubes with a known working set and done the chopstick test around the wires of all the preamp tubes. I've also reflowed most joints in the area and on the ground bus. Nothing I've tried so far has had any effect on the noise. I'm really not sure what else to do other than replace the pot. The amp has worked flawlessly for a few days. Can anyone point me in the right direction? Many thanks, John Sun, 20 Apr 2014 18:49:49 -0400 http://ax84.com/bbs/dm.php?id=484210 RE: ECC88 / E88CC linearity(by jazbo8) 6DJ8, D3a & 4P1L (both triode-strapped).Sat, 19 Apr 2014 22:59:12 -0400 http://ax84.com/bbs/dm.php?id=484209 RE: P1eX clean for jazz(by jazbo8) I would just go with the 6SJ7, as the EF86 tends to be microphonic. Sat, 19 Apr 2014 22:49:53 -0400 http://ax84.com/bbs/dm.php?id=484208 RE: P1eX clean for jazz(by Michael McCarthy) jazbo8 and haiku88: Thank you very much for your replies. I'm going to think about the 6SJ7; people use words like "dark", "mellow", "warm", "compressed". Sounds like a good direction. If I were to parallel an EF86 and a 6SJ7 for the first stage, then would it be reasonable to use a 6AV6 for the second stage? I'm not sure I really want 4 tubes altogether, but it doesn't seem like much difference in terms of current, if I'm not mistaken.Sat, 19 Apr 2014 21:43:48 -0400 http://ax84.com/bbs/dm.php?id=484207 RE: Marshall Superlite TMB(by PhilS) <div class="quoteblock" >On 02/12/2014 @ 14:01, N Iversen wrote : I would look more to altering the phase inverter. That's where a lot of the 18 watt's overdriven tones are coming from. Perhaps lowering the grid leak resistors on the el84's from 470k down to 330k or even 220k. </div>I didn't care for the 470K's. I thought the 220K's cleaned up enough for my taste. I'm not sure if 330K will get a noticeable enough difference. It is easy to tack in a pair of 470K's in parallel, which gives you 235K so you can check it out.Sat, 19 Apr 2014 16:42:01 -0400 http://ax84.com/bbs/dm.php?id=484206 RE: Mark L's fx loop(by jazbo8) That's correct, the positive lead connects to the cathode of the 12AX7.Sat, 19 Apr 2014 11:24:15 -0400 http://ax84.com/bbs/dm.php?id=484205 RE: Mark L's fx loop(by Mrwylde) Thanks I should have known that. If C4 is an electrolytic type cap, is the positive side towards the 12AX7?Sat, 19 Apr 2014 11:05:10 -0400 http://ax84.com/bbs/dm.php?id=484204 RE: ECC88 / E88CC linearity(by DanGu) thanks for explanation. By the way, do you know any other good triode which exibits a good linearity at resonable input sensivity? I found 6h30 and e182cc triodes are very good, but the best results I've obtained by now are with the ecc88 as srpp driver. In simulation I get about 0.2% THD @ about 15W of power, which seems good to me for a SE amp, but if It could be done better It'll be wort trying. Oh yes! And 0.6% THD @ about 15W without the negative feedback being used! This seems good to. Suggestions are wellcome :)Sat, 19 Apr 2014 09:50:22 -0400 http://ax84.com/bbs/dm.php?id=484203 RE: P1eX clean for jazz(by haiku88) re: the parallel pentode channel...it might be worth trying a 6SJ7 octal, they were common in the old Gibson's (and the 5C1 Champ) and have the warm jazzy tone you are looking for, also they are in a metal can which helps a lot with keeping noise and hum down...easy to find NOS for reasonable prices and FWIW 5693 is the HD/long life versionSat, 19 Apr 2014 08:17:37 -0400 http://ax84.com/bbs/dm.php?id=484202 RE: Mark L's fx loop(by jazbo8) <div class="quoteblock" >On 04/19/2014 @ 07:08, Mrwylde wrote : Thanks for the help with this . For caps C1,C3,C5, I think you stated that they were non polarized and 450v right? so their value is 22uF/450v ? </div> No, they should be 22nF = 0.022uF. n means nano, or 10E-9.Sat, 19 Apr 2014 07:16:35 -0400 http://ax84.com/bbs/dm.php?id=484201 RE: Mark L's fx loop(by Mrwylde) Thanks for the help with this . For caps C1,C3,C5, I think you stated that they were non polarized and 450v right? so their value is 22uF/450v ?Sat, 19 Apr 2014 07:08:41 -0400 http://ax84.com/bbs/dm.php?id=484200 RE: Anode and cathode resistor effect on frequency response(by steve25) Resistor wise for guitar amps, nothing much, applying higher plate voltages will increase high end response a good deal though!Sat, 19 Apr 2014 06:11:58 -0400 http://ax84.com/bbs/dm.php?id=484199 RE: Marshall Superlite TMB(by mac dilard) Zaphod Phil would be throwing a fit if he knew you were trying to make this amp be cleaner..He is all about distortion with the 18 watt Marshalls. I have built this amp and the 18 watt IIb. Fun ampsSat, 19 Apr 2014 05:31:03 -0400 http://ax84.com/bbs/dm.php?id=484198 RE: 8" Celestion(by Hughs Wattwerx) I recently acquired 4 of these, NOS, on Ebay. Sound is absolutely stunning. First one went into a tiny 40W 1X8 combo, and I plan to build three more. Checked out Weber and and several other sources (including Celestion), but none of the current offerings have the power handling capability (60W) of the Classic 8. I tried a few high-power eights made for car sound systems, but they all sounded awful -- way too stiff. I've side-by-sided this amp with the internal speaker against the same amp plugged into an external 2X12 loaded with Webers and even with my 'gold-standard' Altec 417, and it compares surprising well, both in terms of tone and volume. If I can get some more of these I'm considering a 4X8 sland-front mini half-stack, maybe paired up with a scaled down Marshall-style head with a pair of KT120s making 100W . . .Sat, 19 Apr 2014 03:29:00 -0400 http://ax84.com/bbs/dm.php?id=484197 RE: P1eX clean for jazz(by jazbo8) <div class="quoteblock" >On 04/18/2014 @ 10:22, Michael McCarthy wrote : : Here are some questions: : : How important are grid resistors on the input stages, and which direction (higher or lower values) would you recommend? </div> If you do not have problem with RF interference, you can make the grid resistors of the input stage as small as possible to reduce the noise. Try 2.2k's for example. <div class="quoteblock" >: I don't have his book yet. Since I don't want this to be too bright, I think the cathode bypass (C25) should be larger, say 4uF. That should get me down to about a drop D fundamental I think. Is there any problem changing that cap value?</div> No problem at all, you can change it to suit your taste, but usually you don't want too much lows on the first stage. : <div class="quoteblock" >: I think I will experiment with larger values on the coupling caps of the parallel input stages (C15 and C23). Again here, the intent is warmer and darker. Vox uses a rotary switch for 6 different caps on the EF86, but they are mostly in the bright direction. Any comments on coupling cap values?</div> Again, it is a matter of personal taste, for jazz, I would use larger values, but probably nothing above 0.047uF. : <div class="quoteblock" >:Could I eliminate R30 and use a lower value on R31? Should I go back to a 12AX7 instead of the 5751 so that the gain of the two parallel input stages will be more balanced?</div> R30 & R31 form a resistive mixer, so both should stay. And using the 12AX7 will give you a bit more gain to better match the gain of the EF86. : :<div class="quoteblock" > Would bright caps be a good idea around VR5 and R30, for more contrast between the two channels?</div> Sure, why not, you can even put it on a switch. : :<div class="quoteblock" > Should I add a grid resistor on the second stage, like the October Studio?</div> That's optional, if you don't have problem with blocking distortion, I would not bother. : :<div class="quoteblock" > The value I selected for R29, to give me B+ of 240V for the EF86 is a shot in the dark.</div> I'm not sure you even need the extra voltage node, you can just use B+3, and adjust the plate and/or the screen resistor of the EF86 to get the correct operating voltages. Besides, the tubes are very tolerant devices, +-20% change in the operating voltages would not make that much a difference. Fri, 18 Apr 2014 23:02:34 -0400 http://ax84.com/bbs/dm.php?id=484196 RE: Marshall Superlite TMB(by JMPGuitars) Two other ways to increase your headroom: 1. The not-too-hard way: increase the B+ voltage a little. Typically we like to see around 340VDC for standard builds. 2. The easy/best way: use a higher efficiency speaker. Perceived volume doubles every 3db of speaker efficiency. I think Greenbacks are about 97db efficiency, I'm currently using an Eminence Red Fang which I love, and I think it's 103db efficiency. That 6db jump gives a big bump in volume/headroom. For me option 2 is the best way because you don't need to make changes to the circuit that can change the tone and responsiveness that makes the 18 Watt the magic amp that it is.Fri, 18 Apr 2014 17:08:09 -0400 http://ax84.com/bbs/dm.php?id=484195