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Jca50H / 100h/ 22h mod thread and owners club

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  • Quote Originally Posted by Edge11
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    I'd d jj in v1 sovtek in v2 and either jj or chinese pre amps in the rest, whatever sounds better.

    Well which mods are you talking about the 12dw7 or the clean switch+scoop?




    Thanks I'll give that a go, got those tubes. Do you know what valves are original to these amps, are they Chinese 12ax7b? Not sure about modifying it yet, I just want to get a good basic rock sound without pedals so I'll give your suggestion a try first. I really don't like the fx loop.

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    • Quote Originally Posted by rmonroe
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      Are you talking about the volume drop using the effects loop? If so I use a Barber Launch Pad in the effects loop to boost the signal. It has made all the difference for me.




      Hi!! No, is not about the loop. I'm wondering to do the CLEAN MOD. But also I read about volume drop in doing that mod... I wanna more clean headroom, so I am in doubt.. tnks

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      • The original was chinese ones. I'm looking to do the clean mod and the mid scoop mod too. But seems that these mods make some drop in volume really noticeable. I wanna make it more clean but also with good headroom, if possible.. thks

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        • Anyone know what the resistor number is on the JCa22H to do the choke mod?

          Also, is it the same procedure where you just remove the resistor and solder in the choke in its place?

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          • Quote Originally Posted by YuriOdeb
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            Hi!! No, is not about the loop. I'm wondering to do the CLEAN MOD. But also I read about volume drop in doing that mod... I wanna more clean headroom, so I am in doubt.. tnks




            you just turn up the master volume to compensate.







            Quote Originally Posted by YuriOdeb
            View Post

            The original was chinese ones. I'm looking to do the clean mod and the mid scoop mod too. But seems that these mods make some drop in volume really noticeable. I wanna make it more clean but also with good headroom, if possible.. thks




            Again you just turn up the mv to compensate. Also you can throw those mods on a switch.
            Jca 50h/ 100h/ 22h Mod thread and Owners Club
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            • Quote Originally Posted by JunkGear
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              Anyone know what the resistor number is on the JCa22H to do the choke mod?

              Also, is it the same procedure where you just remove the resistor and solder in the choke in its place?




              Same procedure don't know the resistor number because I haven't seen the schematic for the 22.
              Jca 50h/ 100h/ 22h Mod thread and Owners Club
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              • Quote Originally Posted by Edge11
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                Same procedure don't know the resistor number because I haven't seen the schematic for the 22.




                Looks like the power sections of the 20 and the 22 are very similar. The resistor number on the 22 is R52

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                • Quote Originally Posted by Edge11
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                  you just turn up the master volume to compensate.



                  Again you just turn up the mv to compensate. Also you can throw those mods on a switch.




                  Thanks everybody for the responses! Now I am using the clean channel with pre on 3 and master on 7. Do you think that will not be a problem?

                  just wonder if I

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                  • Quote Originally Posted by rmonroe
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                    I finally broke down and bought a bias kit to check the bias on my 50 watt Jet City. I am not sure what it was set at, but I believe it was actually too hot. A few months ago I changed out the power tubes with a pair of Sovtek 6L6WXTs but couldn't check the bias. Now that I have I am somewhat disappointed. I paid for a matched and balanced set but the bias on one is off about 5 volts from the the other. I settled on the first being at 44 volts and the second on 39 volts. I first tried 50 on on and 46 on the other, but that sounded harsh. I tried the recommended 37 and it did sound clear and nice, but lacked punch. At 44 and 39 I am happy. I am however thinking about replacing the tubes with JJ KT66s. Can someone recommend a good place to buy them?




                    Made some adjustments to my jca100h today. I made a bias rite type probe over the weekend using an old valve base from a el34, part an old light fitting, three resistors and some wire, cost near enough nothing to make. Tested on my home built point to point wired 6v6 amp first. Finally used it on the jca100h.



                    The jca100h was biased very cold and the valves were quite out of balance.

                    Valve 6 current was 10ma and the anode voltage was 510 volts grid two voltage 506.

                    Valve 7 current was 20.1ma and anode voltage was again 510 volts grid two voltage 506.

                    Valve 8 current was 24.7ma and anode voltage was again 510 volts grid two voltage 506.

                    Valve 9 current was 19.7ma and anode voltage was again 510 volts grid two same 506.



                    Valve 6 and 8 were quite a bit out of balance so i paired them together by swapping valve 6 with valve 9. This balanced the current draw out a little better for each pair 17.35 and 19.9ma respectively.



                    Using loading chart from Duncan

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                    • nice work guyS!! Ill be doing the slo mod and the depth mod fri so a big ol thank you

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                      • Quote Originally Posted by mesa50w
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                        nice work guyS!! Ill be doing the slo mod and the depth mod fri so a big ol thank you




                        You are welcome.

                        Jca 50h/ 100h/ 22h Mod thread and Owners Club
                        Jca20H Mod thread and owners club
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                        • how close are the jca20 and the 22h? I ask beacuse I have a 20h and the slo mod schem is for a 22h. Im fairly sure my amp guy (hes helping me do it) can figue it out but thought id ask any way. Im totaly new at all this Ive only modded a few pedals a ts9 and a handfull of sd-1's. ALso Im planing on using my pedal parts supplier small bear and mouser for the slo mod parts. My stand by switch went out on my 20h last night so Im going to have to wait till it comes in to do the mods now



                          But on a happy not I built one of the litte radio shack attenuators last night and it ripzz! mono speaker control was 19 bucks, 2 input jacks, 5 bucks for a encloser total was around 30 bucks to build it and it works great with the little jca20

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                          • Hello boys,



                            First time posting. Very cool forum, I must say. I just returned my 20h to get a 22h since I discovered that the extra channel was dirtier and not cleaner.



                            I, too, am interested in the foot-switchable dual master volume mod. I have a Krank and JCM 900 SL-X that both have this feature, and I think it is better than sliced bread for solo level boosting. This type of mod would be great in many other amps I have, so info on how to do this would be invaluable. Thanks in advance, and long live internet forums!

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                            • Quote Originally Posted by mesa50w
                              View Post

                              how close are the jca20 and the 22h? I ask beacuse I have a 20h and the slo mod schem is for a 22h. Im fairly sure my amp guy (hes helping me do it) can figue it out but thought id ask any way. Im totaly new at all this Ive only modded a few pedals a ts9 and a handfull of sd-1's. ALso Im planing on using my pedal parts supplier small bear and mouser for the slo mod parts. My stand by switch went out on my 20h last night so Im going to have to wait till it comes in to do the mods now



                              But on a happy not I built one of the litte radio shack attenuators last night and it ripzz! mono speaker control was 19 bucks, 2 input jacks, 5 bucks for a encloser total was around 30 bucks to build it and it works great with the little jca20




                              Never heard of those attenuators.

                              The 20h is the "normal" channel of the 22/50/100/slo. Check out my 20h thread. Lots of good mods there, especially the "super sucker punch" mod.
                              Jca 50h/ 100h/ 22h Mod thread and Owners Club
                              Jca20H Mod thread and owners club
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                              • Had Slo mod done kept stock pots. OD channel gain much smoother less fizz. Love it. Depth mod done noticed with 1 meg pot I hear tone change only in the first 1/3 of rotation. Would 500k be better? Also effects noticable when at low volume under 3 mv.
                                Jet Setters (Jet City Lounge)

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