Members SciHi Posted January 16, 2011 Members Share Posted January 16, 2011 Originally Posted by axe_2_grind Just replaced the remaining stock tubes (v3 & v7) with Mesa 12ax7's and replaced the power tubes with Mesa's as well. Rebiased, and now the thing is smokin!! Sounds like a marshall now. m/ Mine too, but I added a 200R 5 watt sag resistor, then 1K 5 watt before the 10H choke, and changed out the screen resistors to 1.2k 5 watters. I think about half the problems was getting power tubes that sounded good with such high plate and screen voltages, mine was running 365 v on the plates and 350+ on the screens. Dropped those all down now to reasonable levels, 335v on plates and under 320v on screens and it sounds great with any power tubes... Now I wish I hadn't done all the preamp mods, did so many not sure which were really important. I do need to go back in later and change out the dropping resistor for the PI, 10k is really too big now that all the voltages are dropped up front, probably something in the range of 2.7k-4.7k. It will get a test run tomorrow morning at church. So I got some Mesa 6L6 from the Shuguang factory that are really nice and EL34 that aren't bad, but not too sure about their EL84's??? Link to comment Share on other sites More sharing options...
Members diagrammatiks Posted January 16, 2011 Members Share Posted January 16, 2011 just finished up wiring a clean channel Link to comment Share on other sites More sharing options...
Members eyebanez333 Posted January 16, 2011 Members Share Posted January 16, 2011 ^sounds good min depth knob and front panel done....choke is backordered; not sure if I'm even going to bother with it. This amp does exactly what I need it to...and it probably won't ever be my main gig amp. I don't think I'm going to do much else with it. 100% recommend the depth knob though Link to comment Share on other sites More sharing options...
Members axe_2_grind Posted January 16, 2011 Members Share Posted January 16, 2011 Originally Posted by SciHi Mine too, but I added a 200R 5 watt sag resistor, then 1K 5 watt before the 10H choke, and changed out the screen resistors to 1.2k 5 watters. I think about half the problems was getting power tubes that sounded good with such high plate and screen voltages, mine was running 365 v on the plates and 350+ on the screens. Dropped those all down now to reasonable levels, 335v on plates and under 320v on screens and it sounds great with any power tubes... Now I wish I hadn't done all the preamp mods, did so many not sure which were really important. I do need to go back in later and change out the dropping resistor for the PI, 10k is really too big now that all the voltages are dropped up front, probably something in the range of 2.7k-4.7k. It will get a test run tomorrow morning at church. So I got some Mesa 6L6 from the Shuguang factory that are really nice and EL34 that aren't bad, but not too sure about their EL84's??? They Sound Pretty good so far to me. The harshness and fizziness is gone now. Can't wait to take it down to the studio and crank it up again. Sounds awesome already though. I might do a mod to boost the gain just a touch, but so far it's got the 80's metal gain without needing an OD in front. I just want to get it to go a bit further though. I might also do the clean channel mod just to have some versatility out of this amp. I'm kinda giving up on the reverb for now, since I do plan on doing an effects loop anyway. I'd like to try the Zero Loss loop, but I'm not sure if it will fit the combo. The jacks are situated perpendicular to the board. The weber loop kit might work but it just seems like more work on the chassis than I care to do. Or I could go unbuffered. Any recommendations? I plan on using pedals with this amp. Link to comment Share on other sites More sharing options...
Members drmrboy5150 Posted January 16, 2011 Members Share Posted January 16, 2011 Got to listen to the JCA22H this weekend at the NAMM show, it sounded great I can't wait to get one ! Also tried out one of their new reverb/chorus/flanger pedals, sounded really good. Link to comment Share on other sites More sharing options...
Members turnituploud Posted January 17, 2011 Members Share Posted January 17, 2011 that one has 5 preamp tubes. damn.Oh, and i have been experimenting pretty intensely with a l-pad attenuator for the last 2 days, and the -12db attenuation(13ohms in series and 5 in parallel for a 16ohm out) is really neat. It sounds way more fuller in the bass, more dynamic and the highs really stand out, compared to a setting without the attenuator and on the same loudness(5 on master volume compared to 2). And no, the treble loss is, although noticeable, quite small.Also played around with the bias pot: The 17-18 and the 25-26 mA are the sweet spots imo. Still cant decide which one i like best. Link to comment Share on other sites More sharing options...
Members monster265 Posted January 18, 2011 Members Share Posted January 18, 2011 Jet City JCA2112RC combo 8 ohm load. Called Jet City here is the scoop.Manual lacking description regarding the 8 ohm Speaker output.16 ohm output - connect the internal speaker to this position, as the supplied Eminence Speaker impedance is 16 ohms.x2 8 ohm output - Indicates 8 ohm total load. Connect two 16 ohm speaker cabs (equates to 8 ohms) or one 16 ohm cab and the internal Eminence Speaker or one 8 ohm cab. In any case, disconnect the internal Eminence Speaker from the 16 ohm position when using the x2 8 ohm position.. Link to comment Share on other sites More sharing options...
Members Yarbicus Posted January 18, 2011 Members Share Posted January 18, 2011 Originally Posted by monster265 Jet City JCA2112RC combo 8 ohm load. Called Jet City here is the scoop. Manual lacking description regarding the 8 ohm Speaker output. 16 ohm output - connect the internal speaker to this position, as the supplied Eminence Speaker impedance is 16 ohms. x2 8 ohm output - Indicates 8 ohm total load. Connect two 16 ohm speaker cabs (equates to 8 ohms) or one 16 ohm cab and the internal Eminence Speaker or one 8 ohm cab. In any case, disconnect the internal Eminence Speaker from the 16 ohm position when using the x2 8 ohm position.. Hm...that should be in the manual (I wrote it). I'll have to check on that. Link to comment Share on other sites More sharing options...
Members Yarbicus Posted January 18, 2011 Members Share Posted January 18, 2011 Originally Posted by drmrboy5150 Got to listen to the JCA22H this weekend at the NAMM show, it sounded great I can't wait to get one ! Also tried out one of their new reverb/chorus/flanger pedals, sounded really good. Excellent! Yeah, the JCA22H is pretty much a dream come true. Glad it lives up to its potential! That pedal is called the Sonic Boom. I am pretty impressed by all of the JCA pedals and I needs me some reverb. Might have to snag one! Link to comment Share on other sites More sharing options...
Members diagrammatiks Posted January 18, 2011 Members Share Posted January 18, 2011 Just finished the first round of modding.thoughts? Link to comment Share on other sites More sharing options...
Members Edge11 Posted January 18, 2011 Author Members Share Posted January 18, 2011 Originally Posted by diagrammatiks Just finished the first round of modding. thoughts? Sweet video, your clean channel sounds way different than mine. what have you complete so far? Mines more of an bassman type clean sound and when i crank it it's like a roaring plexi. Link to comment Share on other sites More sharing options...
Members axe_2_grind Posted January 19, 2011 Members Share Posted January 19, 2011 Originally Posted by monster265 Jet City JCA2112RC combo 8 ohm load. Called Jet City here is the scoop. Manual lacking description regarding the 8 ohm Speaker output. 16 ohm output - connect the internal speaker to this position, as the supplied Eminence Speaker impedance is 16 ohms. x2 8 ohm output - Indicates 8 ohm total load. Connect two 16 ohm speaker cabs (equates to 8 ohms) or one 16 ohm cab and the internal Eminence Speaker or one 8 ohm cab. In any case, disconnect the internal Eminence Speaker from the 16 ohm position when using the x2 8 ohm position.. Wow, Holy crap! How'd they manage to screw that up? Mine came with the speaker plugged into the middle 8ohm jack right out of the box. Also, Just for s#!ts and giggles, I tried unhooking the reverb cables, and plugging in my Boss DD3 delay with 1/4" to RCA cables. With a medium gain setting it wasn't too bad, in fact it seemed to give the pedal an analog delay quality. But when I maxed the preamp gain, it sounded horrible. It's as though the circuit is somehow distorting the delay output. Maybe the input signal is too strong for the pedal I dunno, but it does seem a bad idea to use the reverb send/return as a poor man's fx loop. Link to comment Share on other sites More sharing options...
Members turnituploud Posted January 19, 2011 Members Share Posted January 19, 2011 Originally Posted by axe_2_grind Wow, Holy crap! How'd they manage to screw that up? Mine came with the speaker plugged into the middle 8ohm jack right out of the box. Also, Just for s#!ts and giggles, I tried unhooking the reverb cables, and plugging in my Boss DD3 delay with 1/4" to RCA cables. With a medium gain setting it wasn't too bad, in fact it seemed to give the pedal an analog delay quality. But when I maxed the preamp gain, it sounded horrible. It's as though the circuit is somehow distorting the delay output. Maybe the input signal is too strong for the pedal I dunno, but it does seem a bad idea to use the reverb send/return as a poor man's fx loop. i guess thats because it goes through another gain stage afterwards. So, yeah, gonna buy a 12au7 tube and some components, and make a loop after the mv control. Btw, have done VH4's and some other mods to the amp, and it is now harmonizing the lower notes a 12th lower. I have read that that may be because of the capacitors(i have put the ones rated 200v, instead of the stock 400v), so i'll play around that bit. Link to comment Share on other sites More sharing options...
Members SciHi Posted January 19, 2011 Members Share Posted January 19, 2011 Originally Posted by axe_2_grind Wow, Holy crap! How'd they manage to screw that up? Mine came with the speaker plugged into the middle 8ohm jack right out of the box... Mine stock was ~365 volts on the plate and ~350 volts on the screens, that is high for EL84's... So just run it where it sounds best!!! Link to comment Share on other sites More sharing options...
Members 333 Posted January 19, 2011 Members Share Posted January 19, 2011 erikm5150 can you tell me what voltage on .68uf and 22uf cathode cap. Been looking for .68uf 25v, searches turn up nothing. Link to comment Share on other sites More sharing options...
Members rock_mumbles Posted January 19, 2011 Members Share Posted January 19, 2011 Originally Posted by SciHi I recommend the 8 ohm tap for a 16 ohm speaker, the reflected impedance of the output transformer is 3.6k plate to plate, and EL84 like something more like 8k, so you run the power amp tubes at 7.2k with the 16 ohm speaker connected to the 8 ohm jack. And as general observation, the higher you are running the plates voltage, the higher you want the reflected impedance. Mine stock was ~365 volts on the plate and ~350 volts on the screens, that is high for EL84's...So just run it where it sounds best!!! I've looked at three JCA2112RC's and all three came with the 16 ohm speaker plugged into the 8 ohm jack ... it won't cause any harm to run the 16 ohm speaker into the 8 ohm tap that runs the output transformer at about 3.8k which is way below what other low reflected impedance EL84 pp amps use ... but if it sounds good use it ...My $0.02 ... most amps run EL84's in push pull at about 8K or so but it does depend on plate voltage ... if the lower reflected impedance sounds better use it i.e. plugging the 16 ohm speaker into the 8 ohm tap Link to comment Share on other sites More sharing options...
Members rock_mumbles Posted January 19, 2011 Members Share Posted January 19, 2011 Originally Posted by 333 erikm5150 can you tell me what voltage on .68uf and 22uf cathode cap. Been looking for .68uf 25v, searches turn up nothing. The 0.68uf cathode caps are film caps, not electrolytic caps so you won't find them less than about 100V rated. Link to comment Share on other sites More sharing options...
Members adamr Posted January 19, 2011 Members Share Posted January 19, 2011 Just received my JCA combo from Ledvedder. All ready has a choke and I have the parts for the depth mod. Just ordered a pair of JJ 84s and 3 Tung Sol 12AX7s. 1 power tube broke durring shipping so I cant try it out till the new tubes arrive. :-( Link to comment Share on other sites More sharing options...
Members axe_2_grind Posted January 20, 2011 Members Share Posted January 20, 2011 anyone else notice a difference between the current on the blue wire vs. the brown wire? I've noticed when biasing (and I'm following Duess's(vh4's) instructions), that the current on the brown wire is significantly less than what's on the blue wire. For example I'm getting approximately 23.3mA (which is about where it should be) on the blue wire, however I get something like 15.5mA on the brown wire. Any ideas what's going on and should I be concerned? Link to comment Share on other sites More sharing options...
Members BSS Posted January 20, 2011 Members Share Posted January 20, 2011 Originally Posted by axe_2_grind anyone else notice a difference between the current on the blue wire vs. the brown wire? I've noticed when biasing (and I'm following Duess's(vh4's) instructions), that the current on the brown wire is significantly less than what's on the blue wire. For example I'm getting approximately 23.3mA (which is about where it should be) on the blue wire, however I get something like 15.5mA on the brown wire. Any ideas what's going on and should I be concerned? I'm no expert, but it could be that your power tubes aren't matched the greatest. Mine is pretty close from wire to wire if I remember correctly (something like 1 mA difference), it's been a while since I biased though. Link to comment Share on other sites More sharing options...
Members erikm5150 Posted January 20, 2011 Members Share Posted January 20, 2011 Originally Posted by 333 erikm5150 can you tell me what voltage on .68uf and 22uf cathode cap. Been looking for .68uf 25v, searches turn up nothing. From my memory, they are 50v electrolytic types. Link to comment Share on other sites More sharing options...
Members Edge11 Posted January 20, 2011 Author Members Share Posted January 20, 2011 Originally Posted by BSS I'm no expert, but it could be that your power tubes aren't matched the greatest. Mine is pretty close from wire to wire if I remember correctly (something like 1 mA difference), it's been a while since I biased though. This, mine have a 5 ma difference. Link to comment Share on other sites More sharing options...
Members Jack Tone Posted January 20, 2011 Members Share Posted January 20, 2011 Jet City must save some money by getting their tubes from the bottom of the barrel. When I checked my 100h with my Weber, the difference between the inner and outer sets was 10mA. I didn't bother checking them individually, just chucked them. Link to comment Share on other sites More sharing options...
Members axe_2_grind Posted January 22, 2011 Members Share Posted January 22, 2011 swapped around my preamp tubes the other day and reseated the power tubes, (and double checked the bias). I put the JJ 12AT7 in V2, and a JJ ECC83S in V1. Put the other JJ ECC83S in V7, and put the mesa 12ax7's in v3 & v4.Reverb seems to have gotten quieter (not that I care), Gain seems a bit sweeter and tighter. Cleans up nicely up until 2.5 on the preamp gain. Good enough to run a distortion and delay in front though (ditched my DS-1 for my modded Metal Zone BTW, it just sounds more organic than the ds-1). With the gain cranked it has that nice JCM800 drive. If I give a bit of clean boost up front, it adds a little extra oomph. I think I'm gonna leave the tubes alone now. Though I may still experiment with the reverb driver later when I get a few different tubes. (I think I'll get some balanced JJ 12ax7's) Link to comment Share on other sites More sharing options...
Members UGQuest Posted January 22, 2011 Members Share Posted January 22, 2011 Originally Posted by UGQuest I think I will buy a used 12"Celestion g12m70 & build my own speaker cab for this head. Has anyone else built their own cab? So far I really like this head, I am going to try some jj/tesla 12ax7 just because of the comments I have read on here. I did the Bitmo Surfra mod and it is pretty cool. I did build my speaker cab with the above speaker & it is sooo loud. I couldn't imagine anyone thinking this 20 watts too weak. I tried the tubes also but ended up sticking with the Tung Sol. I may end up trying a choke later. Link to comment Share on other sites More sharing options...
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