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  • Quote Originally Posted by Jack Tone
    View Post

    There are a few alternatives, but I have the Weber BiasRite:



    http://taweber.powweb.com/biasrite/br_page.htm



    If you change tubes a lot, or have several amps, it's invaluable. I like the Weber because it reads both plate and cathode voltage. I've got the one that reads both 8 pin and 9 pin tubes, but if you scroll down the page, they now have an adapter which will still show both currents, but plugs into your multimeter (the V1 option)...pretty cool!



    Also, if you like to solder, there's this kit from Tube Depot:



    http://www.tubedepot.com/bt-biasrite.html




    Wow - that kit is perfect. Measures both current and plate voltage, and only $16! The assembled one I got from Eurotubes worked ok, but it only measures current and I hate probing the pins for voltage reading while the amp is running.



    And yes, you really should adjust your bias if you can - pretty much a consensus that JCA sets the bias 'cold', which is likely to promote tube life. Bias + JJs made a massive difference on my JCA50H. It's pretty easy to do if you're even somewhat mechanically / electrically inclined, and it'll save you $$$ the first time you do it. Just be really careful about working inside the chassis so's you don't blow yourself up! See Edge's warnings and guidelines on the first post of this thread...



    As to the baffle, I posted a pretty detailed outline of how I built mine up above (see post #129). It can be even easier than that if you just want a simple grill and don't care about having to use screws or what the edges look like. Home Depot has a piece of 24" x 12" expanded metal in the hardware isle that's like $10. Cut it to size using a hacksaw, dremel, or whatever - paint - install using screws, washers, standoffs, etc. to taste, and rock out! I've also seen posts by people doing similar using rain cutter grate, rolling the edges to make it stand taller, etc.
    Come join us at the NEW Jet City Lounge on guitarampboard.com: http://www.guitarampboard.com/forum/...php?f=5&t=1615

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    • Quote Originally Posted by clay189
      View Post

      Edge is there any way I could get you to post a pic of the scoop mod and the cathode bypass, I just want to see a visual of them. I am very new to this reading electronic schematics I have went so far as buying science projects from radio shack for my son and building them just so I can get my skills up with soldering resistors and caps to tiny perf boards. like the scoop mod I understand the soldering the 1m resistors in series but when you solder the cap in the middle then to ground not sure where ground is. I know thats stupid but thats my question Thanks.




      Since Edge hasn't had a chance to reply (he's pretty busy with school these days, it appears), I took the liberty of putting something together, which is what I think he's talking about. I picked up ground off one of the resistors (pretty sure it was R49) near the input jack, which is where I put my switch. I'll try to get a gut shot of my hatchet job this weekend to post up. You can also run a wire to the back of the chassis and pick up ground off the speaker jacks.



      Note - I haven't tried this actual wiring. I originally put in two switches so I could try them independently, and have since removed the cathode bypass. If this is right (Edge - please let me know), I'm probably going to rewire to this, based on his recommendation above.







      Other particulars:

      .001uf cap is ceramic, and may be labeled 1000pf (mine was).



      From Edge:

      "22uf is 50v or more.

      the .001uf is 1kv (most common value)"
      Come join us at the NEW Jet City Lounge on guitarampboard.com: http://www.guitarampboard.com/forum/...php?f=5&t=1615

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      • I am very new to this tube amplifier tinkering but I would have to second what the others have told you. I have a Amp-Head dual bias probe that measures plate voltage and current this tool is a must. I believe everything can be done by you if you are half way mechanical inclined its just like when I take my Harley to the shop and they the tech tells you it has to be done there and you find out if you have the right tools and the information to do it, it's easy to do. these guys on here can help you with anything you and are very knowledgeable. my Jca50h blew me out of the water after a tube change, depth mod and rebias.






        Quote Originally Posted by rmonroe
        View Post

        I bought a JCA50h about a month ago and since changed the power tubes to Sovtek 6L6WXT+ and recently purchased 5 12AX7LPS preamp tubes. I noticed a great improvement when replacing the powertubes even though I do not have the equipment to bias them. In fact Jet City told me I did not need to bia them, but on this forum I am seeing otherwise. Now I am pretty sure there is no need to bias the preamp tubes, or at least that is what my research has shown, but should I get the power tubes biased? The problem is I do not have the equipment to do it on my own and live far from anyone who could do it for me. Also the head is pretty heavy and with my bad back I should not be lifting it. Any advice?



        On a different note, I have seen in this forum that people have made their own metal baffles for their JCAs. Does anyone have a link to detailed instructions on how to so this? Thanks




        Jet Setters (Jet City Lounge)

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        • Quote Originally Posted by GRIMESPACE
          View Post

          Since Edge hasn't had a chance to reply (he's pretty busy with school these days, it appears), I took the liberty of putting something together, which is what I think he's talking about. I picked up ground off one of the resistors near the input jack, which is where I put my switch. I'll try to get a gut shot of my hatchet job this weekend to post up. You can also run a wire to the back of the chassis and pick up ground off the speaker jacks.







          Other particulars:

          .001uf cap is ceramic, and may be labeled 1000pf (mine was).



          From Edge:

          "22uf is 50v or more.

          the .001uf is 1kv (most common value)"





          Edge - your thoughts?




          Thanks Grim the depth mod is badass.

          Thanks aain
          Jet Setters (Jet City Lounge)

          Comment


          • Today I changed preamp tubes to JJs and biased the amp. I was pretty cold with something like 10mA. With a measured plate voltage of 468V I calculated a 70% value of 37mA and that's what I set to bias to.

            I measured plate voltage with a DMM and used an adapter like this to read the bias:





            Overall sound has improved quite a lot but still too much compression for my taste. Looking forward to use other tubes in the power section: 6L6GC-STR RCA-Style black-plate TAD PREMIUM Selected



            That is a recommendation from the guys at Tube Amp Doctor for an open tone.
            Proud Member of the Jet Setters (Jet City Lounge)

            * ENGL Powerball * Jet City JCA100H w/simple clean mod, depth mod * Line6 Spider Valve HD100 Mk1 *
            * Marshall 1960AV loaded with V30s * ISP G Major *

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            • In case anyone is interested, they also suggest this, for an open but warm sound:



              V1: 7025 WA

              V2: 7025 S

              V3-5: ECC83 WA



              This combination costs around twice of the JJs that's why I postponed that for now
              Proud Member of the Jet Setters (Jet City Lounge)

              * ENGL Powerball * Jet City JCA100H w/simple clean mod, depth mod * Line6 Spider Valve HD100 Mk1 *
              * Marshall 1960AV loaded with V30s * ISP G Major *

              Comment








              • Quote Originally Posted by GRIMESPACE
                View Post

                Since Edge hasn't had a chance to reply (he's pretty busy with school these days, it appears), I took the liberty of putting something together, which is what I think he's talking about. I picked up ground off one of the resistors (pretty sure it was R49) near the input jack, which is where I put my switch. I'll try to get a gut shot of my hatchet job this weekend to post up. You can also run a wire to the back of the chassis and pick up ground off the speaker jacks.



                Note - I haven't tried this actual wiring. I originally put in two switches so I could try them independently, and have since removed the cathode bypass. If this is right (Edge - please let me know), I'm probably going to rewire to this, based on his recommendation above.







                Other particulars:

                .001uf cap is ceramic, and may be labeled 1000pf (mine was).



                From Edge:

                "22uf is 50v or more.

                the .001uf is 1kv (most common value)"




                Correct. I use 3pdt switch so when the scoop mod is of it changes the value from 2 1ms to a 680k resistor, aka the normal sucker punch mod.
                Jca 50h/ 100h/ 22h Mod thread and Owners Club
                Jca20H Mod thread and owners club
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                • kocher, so your amp was set at aroiund 10ma from the factory. When i changed my tubes and rebiased I thought I was crazy seeing a 10ma reading. Nice to know I still have my sanity.







                  Quote Originally Posted by kocher
                  View Post

                  Today I changed preamp tubes to JJs and biased the amp. I was pretty cold with something like 10mA. With a measured plate voltage of 468V I calculated a 70% value of 37mA and that's what I set to bias to.

                  I measured plate voltage with a DMM and used an adapter like this to read the bias:





                  Overall sound has improved quite a lot but still too much compression for my taste. Looking forward to use other tubes in the power section: 6L6GC-STR RCA-Style black-plate TAD PREMIUM Selected



                  That is a recommendation from the guys at Tube Amp Doctor for an open tone.




                  Jet Setters (Jet City Lounge)

                  Comment


                  • Edge11...or anyone else...



                    Lately I've been trying to tweak the tone controls/depth/presence controls while playing on the overdrive channel, trying to get that bright/middy hot rodded JCM800 kinda sound, but I always find that the overdrive channel has far too much low/low-mid muscle to do the Marshall sound.



                    Is there a mod for a voicing switch or something similar that would be able to give the OD Channel a more Marshall flavour?
                    My Rig:
                    #1: Jolly Roger Cutlasscaster (Duncan Custom 4/Lil '59)
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                    AudioTechnica Wireless, Boss NS-2, Korg Pitchblack, Boss GE-7, Dunlop Crybaby, Fulltone OCD, TC Nova repeater
                    Jet City JCA100H
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                    Proud Member of the Jet Setters (Jet City Lounge)

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                    • Quote Originally Posted by Blakkwater
                      View Post

                      Edge11...or anyone else...



                      Lately I've been trying to tweak the tone controls/depth/presence controls while playing on the overdrive channel, trying to get that bright/middy hot rodded JCM800 kinda sound, but I always find that the overdrive channel has far too much low/low-mid muscle to do the Marshall sound.



                      Is there a mod for a voicing switch or something similar that would be able to give the OD Channel a more Marshall flavour?




                      Change the slope resistor to 33k
                      Jca 50h/ 100h/ 22h Mod thread and Owners Club
                      Jca20H Mod thread and owners club
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                      • Hey Edge, The depth mod kicks ass and for us beginner moders was simple and smooth so thanks for that. Now for my next rookie ? I am thinking of the Scoop mod but what does this exactly do does it bring the mids down even more than just rolling them back on the Eq. Forgive me if the ? is just plain stupid.
                        Jet Setters (Jet City Lounge)

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                        • Hi looking for a little help with my sons jca22h. My twelve year old son has been playing the jca20 for about a year and his grades earned him an upgrade. Yesterday we got a 22h from an on line retailer. the crunch channel sounds great I think maybe a little fuller then the 20 sounded. The problem is the od channel. When he hits the switch it squeals like a pig in heat and the only thing that will control it is the preamp knob. I emailed jet city and there response all though fast was a little lacking in information. It said to check the tubes to make sure they are glowing. It also said that the amp was designed to plug and play so if a tube is bad you can just get the same kind and put it in. Being a total noob (or kook which ever you prefer) I have know idea where to start. I can only see 5 tubes through the grill and they all have some color some a little stronger then others but color. Any help that you may provide would be helpful. I am not totally mechanically challenged so I am willing to give this tube replacement a try just don't know where to start. By the way v1, v2 v3 etc. mean absolutely nothing to me. Thanks
                          HCGB Trooper #315

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                          • Quote Originally Posted by isuck
                            View Post

                            Hi looking for a little help with my sons jca22h. My twelve year old son has been playing the jca20 for about a year and his grades earned him an upgrade. Yesterday we got a 22h from an on line retailer. the crunch channel sounds great I think maybe a little fuller then the 20 sounded. The problem is the od channel. When he hits the switch it squeals like a pig in heat and the only thing that will control it is the preamp knob. I emailed jet city and there response all though fast was a little lacking in information. It said to check the tubes to make sure they are glowing. It also said that the amp was designed to plug and play so if a tube is bad you can just get the same kind and put it in. Being a total noob (or kook which ever you prefer) I have know idea where to start. I can only see 5 tubes through the grill and they all have some color some a little stronger then others but color. Any help that you may provide would be helpful. I am not totally mechanically challenged so I am willing to give this tube replacement a try just don't know where to start. By the way v1, v2 v3 etc. mean absolutely nothing to me. Thanks




                            V1 is the preamp tube nearest the input jack on the 22h.



                            I would suggest the following:



                            Buy 2 JJ EL84 tubes and 4 SOVTECK 12ax7wa tubes.



                            Unplug the amp and take the back panel off the amp. Then set the amp face down on a soft surface like a rug....remove the 4 screws on the bottom to free up the chasis....then slowly and carefully put the amp back on it's bottom and carefully remove the chassis from the cab....DO NOT touch anything under the chasis....simply slide it out and place it on the floor...this allow you to access the tubes. replace the 2 EL84 power tubes, then replace the 4 12ax7's in V1 to V4 with the sovtecks.



                            This should help out a lot.
                            Originally Posted by chainsaw fats
                            Can I drink your piss?




                            Great people: d_dave_c, wbcsound.

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                            • Thank you for your help. Placing order has we speak. One other thing the metal housings on a few of the tubes do they screw of or just pull off
                              HCGB Trooper #315

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                              • Will he notice much of a difference if I just put JJ's all the way around? thanks for your help.
                                HCGB Trooper #315

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