Members Zhorellski Posted July 14, 2010 Members Share Posted July 14, 2010 How much are the mods? links website? kinda interested on this Amp.. Link to comment Share on other sites More sharing options...
Members Edge11 Posted July 14, 2010 Author Members Share Posted July 14, 2010 Originally Posted by Zhorellski How much are the mods? links website? kinda interested on this Amp.. It's very DIY So far. So the cost of mods is the cost of parts.The only other person that does mods is Dave Friedman.I think his mods run around $3-200. Link to comment Share on other sites More sharing options...
Members Edge11 Posted July 19, 2010 Author Members Share Posted July 19, 2010 ARG!MY light is failing me again, it's flickering on and off!Also I'm adding the instructions for the choke mod.My light just died going to see if its just faulty soldering on my part.please, read the warning and safety measures before you start modding. Link to comment Share on other sites More sharing options...
Members theDogger Posted July 19, 2010 Members Share Posted July 19, 2010 Ok kool thanks for that. So to make sure that I understand in simple terms using a choke in the filter supply the result is less background hum and cleaner, better bass response. Using a resistor manufacturers save time and cost and there is a bit more background hum and a looser bass response. I emailed Mercury Magnetic and they suggested the JTM45 -- 7H -- 150mA. Why did you choose the Hammond 156M 3h-100ma current and 86 ohm DCR??Would changing the output transformer make a difference int he choice of the choke? So the R3 Resistor value is 1k? 5% thanks theDogger Link to comment Share on other sites More sharing options...
Members Duesentrieb Posted July 19, 2010 Members Share Posted July 19, 2010 I'd use a Fender (or replacement) choke for the Deluxe Reverb. 4H, 100R. Search Fender 125C3A. Its small and enough for the JCA20H. Link to comment Share on other sites More sharing options...
Members Edge11 Posted July 19, 2010 Author Members Share Posted July 19, 2010 Originally Posted by theDogger Ok kool thanks for that. So to make sure that I understand in simple terms using a choke in the filter supply the result is less background hum and cleaner, better bass response. Using a resistor manufacturers save time and cost and there is a bit more background hum and a looser bass response.I emailed Mercury Magnetic and they suggested the JTM45 -- 7H -- 150mA. Why did you choose the Hammond 156M 3h-100ma current and 86 ohm DCR??Would changing the output transformer make a difference int he choice of the choke?So the R3 Resistor value is 1k? 5%thankshttp://acapella.harmony-central.com/...ply&p=40352845theDogger A choke is used in place of a series resistor because the choke allows better filtering (less residual AC ripple on the supply, which means less hum in the output of the amp) and less voltage drop(higher B+, so a little more "clean" headroom).In typical designs (such as this) the choke only regulates DC current to the screen grids of the pre and output tubes. each pre amp tube takes about 1-3ma and the output tubes about 10ma.So following this formula a 50 watter would usually need only 50-60Ma.The induction was chosen probably because even at the specs that it is at it is still over kill. You wont get much of a difference with 3h to 7h, once the induction is up to snuff going higher brings much much much much less return. The choke part number I got from deuse, but I'm sure that it was chosen because it was fairly inexpensive (30$ shipped) and it is perfect for the job, hell if anything it's already overspec'd.I don't mean to blast Mercury, but the choke they suggested to you is probably over priced (when compared to the hammond choke) and will not affect the feel of the amp in a more positive way than the Hammond choke. If anything the higher induction of the mercury choke may make the amp feel more stiff, and make it harder to break up. Link to comment Share on other sites More sharing options...
Members barden1069 Posted July 19, 2010 Members Share Posted July 19, 2010 Does anyone know where to get an A1M pot for the depth mod? I tried google but all I got was some confusing stuff and I'm a bit lost now...Told you I'm a noob. Link to comment Share on other sites More sharing options...
Members Duesentrieb Posted July 20, 2010 Members Share Posted July 20, 2010 Mouser, Mojo, Ruby . . . Look for a Alpha 1M log pot. Or 500k. Doesn't really matter. Link to comment Share on other sites More sharing options...
Members BSS Posted July 21, 2010 Members Share Posted July 21, 2010 Just thought I'd offer my experience with a little tube swapping I did;I recently tried following tubes:JJECC803S Gold Pins, Hi-GainJJECC83S Hi-GainElectro Harmonix 12AX7EHSovtek 12AX7LPSTung Sol 12AX7 RINew Sensor Mullard RI 12AX7I also replaced the power tubes with JJEL84'sI tried just about every imaginable combo with these tubes and my results:Balanced Sovtek LPS sounded the best in PI (V3) spot...Most of these I tried with the Hi-gain JJECC83S in V2...803S Gold Pin - Had something weird going on in the mids. Hard to describe. Brighter than the JJECC83S, but still darker than a "normal" 12ax7...83S - Sounded alright, seemed a little too "mushy" in V1.Tung Sol - Pretty good. Articulate, smoother than stock, but a little bright/fizzy.EH - Similar to the Tung Sol, a little less fizz maybe, good gain.Mullard - I finally settled on this tube. I really liked it in my Blackstar. It seems to be pretty smooth, while still retaining good note to note articulation. Good, open, throaty sound.I did try the Tung Sol in V1 with EH in V2. Seemed a touch brighter/fizzier than I wanted. With Mullard RI in V1 and EH in V2, didn't have quite as much gain as with the Hi-gain JJ in V2.I'm really liking the tube combo I've got now. Good amount of gain, smoother with less fizz on the high end with max gain. I went from running almost no presence and treble/mids noon or below to running presence from 4-6 and treble and mids 5-5.5. I think the Mullard and JJ rolled off some of the high end, which is what I was trying to accomplish. Awesome sound when wound up too Link to comment Share on other sites More sharing options...
Members Yarbicus Posted July 21, 2010 Members Share Posted July 21, 2010 Thanks, BSS! That's some good info. Link to comment Share on other sites More sharing options...
Members theDogger Posted July 21, 2010 Members Share Posted July 21, 2010 I am running 2-JJ-EL84 2-JJ-12AX7 Standard (V1 & V2) 1-JJ-12AX7 Balanced (V3) 1-JJ-12AX7 HighGain (V1) 1-JJ-12AT7 Low Gain (V2) 1-Tungsol 12AX7 Standard (V1 & V2) Try this , I did it on accident....run the JJ HG in V3 and the balanced in v1 and normal in v2 It did not sound bad at all I played it this way for a while before I noticed it was backwards when I started to swap the tubes out..........but here is what I settled on 2-JJ-EL84 @22mA bias 1-JJ-12AX7 HighGain (V1) 1-JJ-12AT7 Low Gain (V2) 1-JJ-12AX7 Balanced (V3) I am in the process of adding the BitMo Surfa tonightBSS what did you BIAS the tubes at????? theDogger Link to comment Share on other sites More sharing options...
Members theDogger Posted July 22, 2010 Members Share Posted July 22, 2010 Well did the BitMo Surfa mod late last night. From what I could tell at the level I was at I like it. The install is smooth and easy just take your time. The only change that I am making it to the 2nd switch with by passes the M*style tone stack. with the suggested resistor the Mid and Treb are not active. Bruce supplies a different resistor that give back the mid and treb control. I just found it to be way to VOX'y if you will. But the I am waiting to get home so I can crank the master and enjoy the OD boost. theDogger Link to comment Share on other sites More sharing options...
Members Twebbz Posted July 23, 2010 Members Share Posted July 23, 2010 This is a custom grill from Reliable Hardware Company. It's 3/4 inch bend on all four sides brings it forward and gives it a nice finished look.www.reliablehardware.com Link to comment Share on other sites More sharing options...
Members theDogger Posted July 23, 2010 Members Share Posted July 23, 2010 Does anyone know what the OT is rated at? Is it a single tap or multi tap? I was looking at the schematic and was wondering....Also when I called JCA and asked they told me that the input jacks on the back are misleading. That actually the 2-8ohm outs are meant for 2-16ohm cabs to take it to 8ohms...not 2-8ohm cabs to 16ohms..is that right????? theDogger Link to comment Share on other sites More sharing options...
Members theDogger Posted July 24, 2010 Members Share Posted July 24, 2010 Originally Posted by Twebbz This is a custom grill from Reliable Hardware Company. It's 3/4 inch bend on all four sides brings it forward and gives it a nice finished look.www.reliablehardware.com What were the measurements that you used on the site? How accuratlly did it fit with or without tweaking??theDogger Link to comment Share on other sites More sharing options...
Members Twebbz Posted July 24, 2010 Members Share Posted July 24, 2010 I used 18" wide and 5 1/8" tall with a 3/4 inch bend on all four sides. You may be able to see that I added a 3/4 square strip of wood on each side of the head thinking that I'd have to have something to screw the grill on to. However the grill bends were bent a little outwards so it appeared that the grill was too wide. A little hammering of the bends inward made it a tight fit to the point that fastening with screws was unecessary. Link to comment Share on other sites More sharing options...
Members theDogger Posted July 26, 2010 Members Share Posted July 26, 2010 Can anyone answer this question? I am a little confused by the primary impedance on that OT. Two EL84 tubes in almost every amp we have run across would be around 8k. That sticker is showing a primary impedance of 3.6k. This seems very, very low for two EL84 tubes. Is it not?? If so what would be a good after market upgrade to the OEM OT theDogger Link to comment Share on other sites More sharing options...
Members BSS Posted July 26, 2010 Members Share Posted July 26, 2010 Originally Posted by theDogger I am running 2-JJ-EL842-JJ-12AX7 Standard (V1 & V2)1-JJ-12AX7 Balanced (V3)1-JJ-12AX7 HighGain (V1)1-JJ-12AT7 Low Gain (V2)1-Tungsol 12AX7 Standard (V1 & V2)Try this , I did it on accident....run the JJ HG in V3 and the balanced in v1 and normal in v2It did not sound bad at all I played it this way for a while before I noticed it was backwards when I started to swap the tubes out..........but here is what I settled on2-JJ-EL84 @22mA bias1-JJ-12AX7 HighGain (V1)1-JJ-12AT7 Low Gain (V2)1-JJ-12AX7 Balanced (V3)I am in the process of adding the BitMo Surfa tonightBSS what did you BIAS the tubes at?????theDogger Have not biased yet. Need to get back under the hood andcheck it out when I get time. Link to comment Share on other sites More sharing options...
Members MatchFive Posted July 27, 2010 Members Share Posted July 27, 2010 I assume that these mods will work on the JCA2112RC as well since it is basically the same amp but with reverb in combo form... Link to comment Share on other sites More sharing options...
Members Edge11 Posted July 27, 2010 Author Members Share Posted July 27, 2010 Originally Posted by theDogger I am running 2-JJ-EL842-JJ-12AX7 Standard (V1 & V2)1-JJ-12AX7 Balanced (V3)1-JJ-12AX7 HighGain (V1)1-JJ-12AT7 Low Gain (V2)1-Tungsol 12AX7 Standard (V1 & V2)Try this , I did it on accident....run the JJ HG in V3 and the balanced in v1 and normal in v2It did not sound bad at all I played it this way for a while before I noticed it was backwards when I started to swap the tubes out..........but here is what I settled on2-JJ-EL84 @22mA bias1-JJ-12AX7 HighGain (V1)1-JJ-12AT7 Low Gain (V2)1-JJ-12AX7 Balanced (V3)I am in the process of adding the BitMo Surfa tonightBSS what did you BIAS the tubes at?????theDogger Bias your tubes depending on your situation, the equation for it is on deus' how to bias video.I updated the page to include the jet packs.if any one has any more clips put them up. Originally Posted by TheEternal I assume that these mods will work on the JCA2112RC as well since it is basically the same amp but with reverb in combo form... Probably assuming that the parts are numbered the same. Link to comment Share on other sites More sharing options...
Members BSS Posted July 28, 2010 Members Share Posted July 28, 2010 What will biasing do for the tone? I'd like to pull the chassis tonight and try it. Link to comment Share on other sites More sharing options...
Members theDogger Posted July 28, 2010 Members Share Posted July 28, 2010 Originally Posted by BSS What will biasing do for the tone? I'd like to pull the chassis tonight and try it. It will do a lot per say....if it is cold then it will be fizzy and harsh.....biasing it @ 65%-70% is perfect....really smooth things out and makes it sing!theDogger Link to comment Share on other sites More sharing options...
Members BSS Posted July 29, 2010 Members Share Posted July 29, 2010 Originally Posted by theDogger It will do a lot per say....if it is cold then it will be fizzy and harsh.....biasing it @ 65%-70% is perfect....really smooth things out and makes it sing!theDogger Got it biased after work today. Biased up to ~19.09 mA.My voltage read 368@ 12 watt, 60% = 19.56mA@ 11.5 watt, 60% = 18.75mAI was a bit nervous at first, but thanks to Deus' tutorial, it was a breeze. Thanks Deus!!! Also, mblooper (and all who've contributed), thanks for this thread; it's a great resource for us Jet City owners.It sounds really awesome now, especially at >5 on the volume. Even improved the low volume sound a bit. Link to comment Share on other sites More sharing options...
Members theDogger Posted July 29, 2010 Members Share Posted July 29, 2010 Id take it up to 70% around 21-22mA will sound so much better I still think that 19Ma is on the warm end of cold. Try it it won't hurt it... theDogger Link to comment Share on other sites More sharing options...
Members BSS Posted July 29, 2010 Members Share Posted July 29, 2010 Originally Posted by theDogger Id take it up to 70% around 21-22mA will sound so much better I still think that 19Ma is on the arm end of cold. Try it it won't hurt it...theDogger I was thinking of doing this, so I took some readings again. It appears that my wall voltage sucks (I'm getting upwards of 135 V in my wall outlet). I am getting up to ~380+ V on my B+ at times, then when my A/C kicks on, washer and dryer, etc., it runs back down to as low as 362-364. What voltage should I bias at? It seems that if I bias at one voltage, it's off at another one. Link to comment Share on other sites More sharing options...
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