Members Edge11 Posted December 31, 2010 Author Members Share Posted December 31, 2010 Originally Posted by turnituploud the attached ones. Use the tube that it specifies in the scheme Link to comment Share on other sites More sharing options...
Members Yarbicus Posted December 31, 2010 Members Share Posted December 31, 2010 Originally Posted by StudioPlsCherry You were spot on...I got one of the edges to lift with a putty knife and then managed to wiggle the panel until it finally popped. Also, the amp sounds pretty awesome with V1 replaced with a 12AY7 and V3 with a 12AT7. Specifics? Do those give it a bit more clean headroom? I must know!!! Link to comment Share on other sites More sharing options...
Members SciHi Posted December 31, 2010 Members Share Posted December 31, 2010 Originally Posted by Yarbicus Specifics? Do those give it a bit more clean headroom? I must know!!! I think to get more volume and life with the clean tone you need to reduce the amount of negative feedback. The depth control mod certain does this, but simply moving the nfb wire from the 16 ohm to 8 ohm tap will help, adding about 25% more gain and add some life to the amp. Turning up the presence in effect negates the strong nfb but only for the higher frequencies, it helps add some life to the amp but then you might need a cut control to reduce the ice pick highs... I did a few tests with the nfb, with nfb wire in stock position (16 ohm tap) I just added another 47K resistor, that helped. Last night I tested nfb with a three position switch, on-off-on, where one position was stock 47k to 16 ohm tap, center was no nfb, and other was stock 47k to 8 ohm tap. (Without some nfb however, you lose any presence control.) We are talking night and day differences here... So in addition to clean headroom, the amp needs a little life added for lower gain settings, the stock strong nfb seemed to be really constricting the life out of the amp, well thats my opinion anyway. I am use to 18 watt designs that sing both clean (low gain settings) and overdrive tones...I just put a old JAN 12au7 in v1 and you have cleaner tone up to noon on the gain dial and with the nfb on the 8 ohm tap, you can get ok cleaner tone, not really loud, you can only drive the power tubes so hard also without them distorting. For real clarity and chime with HBs anyway, I think you need to swap out a few parts (resistors/caps) in the preamp. But the lower gain preamp tube seems like a nicer balance between preamp and power tube overdrive-distortion. The 12ay7 would be half way between the 12au7 and 12ax7, but 12au7's are easier to find and NOS much cheaper than a 12ay7 or 5751... Link to comment Share on other sites More sharing options...
Members turnituploud Posted January 1, 2011 Members Share Posted January 1, 2011 Originally Posted by SciHi I think to get more volume and life with the clean tone you need to reduce the amount of negative feedback. The depth control mod certain does this, but simply moving the nfb wire from the 16 ohm to 8 ohm tap will help, adding about 25% more gain and add some life to the amp. Just did this and besides the gain it also boosted the bass a lot and presence a bit. Before that i used to have 3,5 on presence and 7 on bass and now i can turn the presence to 1,5-2 maximum before the ice picks appear and the bass at 3-4, and its still bassy. I guess this is where the choke comes in..And it really gave the amp life, especially on the clean channel. Link to comment Share on other sites More sharing options...
Members SciHi Posted January 1, 2011 Members Share Posted January 1, 2011 Originally Posted by turnituploud Just did this and besides the gain it also boosted the bass a lot and presence a bit. Before that i used to have 3,5 on presence and 7 on bass and now i can turn the presence to 1,5-2 maximum before the ice picks appear and the bass at 3-4, and its still bassy. I guess this is where the choke comes in..And it really gave the amp life, especially on the clean channel. I always use humbuckers and the first coupling cap is really a little large, I think the zh4 mod with 10-4.7nF would be good up front to limit the bass more, he shows changing out the gain pot to A250k also, in conjunction with the small coupling cap this should be better bass control. You want to get the bass under control before you start overdriving - clipping tubes down the line...My experience with chokes is they can really add quality tone character, life and responsiveness, better clarity and definition to the notes. Less noise and more stability to the power supply feeding the high gain preamp tubes... Pretty cheap mod that usually really pays off. Saving money in the long run because you stop buying all the NOS tubes looking for the perfect tube...I think the amp was designed with the high gain tone in mind, which is great if that is all you ever need. I just want mine a little more versatile, may end up adding the extra channel eventually but even a few little changes have helped... Link to comment Share on other sites More sharing options...
Members javipizca Posted January 2, 2011 Members Share Posted January 2, 2011 Hi, I have change tubes to JJ and also made the choke mod to my Jca20H. The B+ reading is 342VDC B+, I have adjusted the bias in all possible forms but still don Link to comment Share on other sites More sharing options...
Members 333 Posted January 3, 2011 Members Share Posted January 3, 2011 Anyone installed a weber effects loop? Got one, missing some parts and no instructions. Link to comment Share on other sites More sharing options...
Members Edge11 Posted January 6, 2011 Author Members Share Posted January 6, 2011 Originally Posted by javipizca Hi, I have change tubes to JJ and also made the choke mod to my Jca20H. The B+ reading is 342VDC B+, I have adjusted the bias in all possible forms but still don Link to comment Share on other sites More sharing options...
Members Fredpott131 Posted January 6, 2011 Members Share Posted January 6, 2011 I picked this amp up a few days ago and I really like it. It has a nasty kind of grit and bite to it (in a good way). Guessing that is the Soldano design in there. There seem to be a lot of posts about getting more clean headroom out of this amp. A split load plate resistor on the first triode might be an option. Do not know how effective it would be as there are a lot of preamp gain stages in this design. Actually one more gain stage than a JCM800 type amp. Link to comment Share on other sites More sharing options...
Members rock_mumbles Posted January 6, 2011 Members Share Posted January 6, 2011 Originally Posted by javipizca Hi, I have change tubes to JJ and also made the choke mod to my Jca20H. The B+ reading is 342VDC B+, I have adjusted the bias in all possible forms but still don Link to comment Share on other sites More sharing options...
Members Edge11 Posted January 6, 2011 Author Members Share Posted January 6, 2011 Originally Posted by Fredpott131 I picked this amp up a few days ago and I really like it. It has a nasty kind of grit and bite to it (in a good way). Guessing that is the Soldano design in there. There seem to be a lot of posts about getting more clean headroom out of this amp. A split load plate resistor on the first triode might be an option. Do not know how effective it would be as there are a lot of preamp gain stages in this design. Actually one more gain stage than a JCM800 type amp. No. jcm 800= 3 stages + cathode follower (P.s. the 10k stage is still a gain stage, we don't need another forum war about that). Jca 20h= 3 gainstages +cathode follower. Link to comment Share on other sites More sharing options...
Members detailman Posted January 6, 2011 Members Share Posted January 6, 2011 Not a mod but for those interested in a good boost pedal for their JCA 20H I highly recommend a DOD YJM308 (Yngwie Malmsteen signature preamp boost pedal). I just got one for use on soloing and riffing and it does the job quite well. It hardly, if at all, colors the tone and provides both gain and volume boost. It has a reputation for being noisy but if you keep the gain under 2:00 it's not. No LED but you can clearly hear when it's on or off. There are lots of mods you can do to it as well. It's heavy, built solid, looks great and you can pick one up for $29.95 plus free shipping from American Musical Supply. Zzounds.com has the same deal but $2.99 for shipping. I was also considering a Jet City GS Hi-Gain Boost pedal but it's $40 more than the DOD YJM308 and I could never find a real review or video of it. Looks really nice, but I'm very happy with my DOD. Link to comment Share on other sites More sharing options...
Members Fredpott131 Posted January 6, 2011 Members Share Posted January 6, 2011 mblooper45...you are correct....my bad. I was thinking of the 1959 type four input marshalls. The 10K cathode resistor/cold clipper gain stage probably does give some voltage gain...not much gain but more than unity. Link to comment Share on other sites More sharing options...
Members javipizca Posted January 6, 2011 Members Share Posted January 6, 2011 Thanks, I Link to comment Share on other sites More sharing options...
Members javipizca Posted January 6, 2011 Members Share Posted January 6, 2011 I Link to comment Share on other sites More sharing options...
Members Fredpott131 Posted January 6, 2011 Members Share Posted January 6, 2011 Thanks, I Link to comment Share on other sites More sharing options...
Members Edge11 Posted January 6, 2011 Author Members Share Posted January 6, 2011 Gonna stick a 12dw7 in v2 as soon as it comes in. Wish me luck guys. Link to comment Share on other sites More sharing options...
Members thehephaistos Posted January 6, 2011 Members Share Posted January 6, 2011 Hi everybody, I'm searching for output transformer replacement for the combo. Does someone has idea what would be the specs ? I changed on my JCA all the caps (except for the reverb part coz i'm cheap!) with orange drops without noticing any improvement in the sound. Thanks a lot Link to comment Share on other sites More sharing options...
Members thehephaistos Posted January 6, 2011 Members Share Posted January 6, 2011 By the way this is two pictures of my JCA combo vs the astroverb of a friend of mine. If it can helps... Link to comment Share on other sites More sharing options...
Members Fredpott131 Posted January 7, 2011 Members Share Posted January 7, 2011 Hi everybody,I'm searching for output transformer replacement for the combo. Does someone has idea what would be the specs ?I changed on my JCA all the caps (except for the reverb part coz i'm cheap!) with orange drops without noticing any improvement in the sound.Thanks a lot There are a lot of good 18 watt push pull output transformers available for EL84 guitar amps. I have used 18-20 watt output transformers from Heyboer and Musical Power Supplies to build some good sounding amps. Classic Tone Transformers, Hammond, and Mercury Magnetics also sell good 18-20 watt output transformers. I pulled the chassis out of the wood case tonight to do some tube swapping. The Output transformer in there certainly looks like it has enough iron in it to do the job. The transformer looks like it is a 3.6K (1.8K/1.8K)...most EL84 push pull amps use 8K reflected load? The power transformer looks a bit on the small side for a 20 watt amp but it really does not seem to get that hot. I did some tube swapping in V1. Tried a EH 12AY7 and a Sylvania 12AX7. The sylvania did smooth out a lot of the fizz so I left it in there. The 12AY7 did cut the gain a bit but the fizz was still there when the gain is cranked. Link to comment Share on other sites More sharing options...
Members anti-flag193 Posted January 7, 2011 Members Share Posted January 7, 2011 Any experiences with the Jet City cabs? Sounds/construction/quality? Mainly interested in the 1x12 Link to comment Share on other sites More sharing options...
Members SciHi Posted January 7, 2011 Members Share Posted January 7, 2011 Originally Posted by Fredpott131 ... The transformer looks like it is a 3.6K (1.8K/1.8K)...most EL84 push pull amps use 8K reflected load? I think most of the fizz-frazz is generated in the preamp so no real impact on it. Link to comment Share on other sites More sharing options...
Members Fredpott131 Posted January 7, 2011 Members Share Posted January 7, 2011 Rock and I found this hard to believe, and actually determined the turns ratio with a small power supply and both the 8 and 16 ohm taps are 3.6K plate to plate. Because this is so low for EL84's, I have been running the 16 ohm speaker in the 8 ohm jack to get the reflected impedance up to 7.2K but honestly can tell a large amount of difference, maybe only when driven hard with reduced NFB does it really help. I think most of the fizz-frazz is generated in the preamp so no real impact on it. I think running at 3.6K reflected impedance would cut some of the low end. 3.6K is certainly not ideal to get good low end frequency out of the OT. It would certainly generate more distortion in the OT itself than an 8K impedance. Link to comment Share on other sites More sharing options...
Members axe_2_grind Posted January 7, 2011 Members Share Posted January 7, 2011 Hey all, I just joined the Jet Setter lounge yesterday when my 2112rc combo arrived. I'm digging this thing, but I do see a need to retube/rebias to get a smoother sound, but overall not bad right out of the box. I do have a couple of quick questions though.1)Where can I get a schematic for this amp (JCA2112RC)?2)What would be a recommended set of preamp tubes to get (brand/type)?I'm a high gain dude mainly, however I've been reading this thread and want to experiment with a 12at7 in various positions as well just to see what it'll do for me.I am planning on rebiasing regardless or at least checking it since I understand they supposedly set these things cold at the factory (dug out my multimeter today). I would also like to add an fx loop and have been looking at the Zero Loss loop. Did the Dogger ever finish installing his? Link to comment Share on other sites More sharing options...
Members mcr23 Posted January 7, 2011 Members Share Posted January 7, 2011 what about a half power pentode/triode? Link to comment Share on other sites More sharing options...
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