NAD Jet City JCA20H - Update New Grill!

Discussion in 'Other Amps' started by Filipe Soares, Aug 10, 2020.

  1. Filipe Soares

    Filipe Soares Well-Known Member

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    I'll probably order with Bryce this week

    1) octal mod (I have a pair of JJ EL34s here. so its almost the same price as replacing the chinese EL84 for something better)

    2) FX Loop - I would normally go with the metropoulos, but it will save me the shipping costs from a different vendor

    3) Brown Iris Phil X - it's the same brown iris mod with 2 extra flavors (switchable)
     
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  2. Filipe Soares

    Filipe Soares Well-Known Member

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    This was the best idea ever. I´ll 3D print something similar to this:

    [​IMG]


    any ideas on how to do a metal front grill to this amp???
     
  3. stickyfinger

    stickyfinger Well-Known Member

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    You mean 394v? I cant imagine 494v and tube life. Had one of these when they first came out. Wast the tone I likes so I modded it and eventually sold it as it never sounded good. Cheap parts or what ever it was but the PCB learning experience was worth the 300$!
     
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  4. Filipe Soares

    Filipe Soares Well-Known Member

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    nope, 494. I´ll check that again later, but it was too high. the good thing is these tubes won´t be in the amp for a long time. my aim is to install some EL34s that I have in my parts bin.
     
  5. J Saw

    J Saw Well-Known Member

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    Yeah. 494 seems way too high. Both of mine run around 360.
     
  6. Filipe Soares

    Filipe Soares Well-Known Member

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    I`ll test with a different multimeter when I´m back home. that was way too weird, but it sounds good!
     
  7. thetragichero

    thetragichero Well-Known Member

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    had the 50w combo that i modded. didn't give any funky names to the mods just figured out what i wanted from the schematic
    not dumping so much gain from the crunch channel makes that where the best tones are. just ends up being louder than the overdrive channel for similar master settings because it's not going through that cold clipper stage with the 39k cathode resistor (can easily be adjusted if you set the knobs with your ears rather than your eyes)

    all in all though i was impressed with the stock build quality. they use some beefy iron
     
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  8. Filipe Soares

    Filipe Soares Well-Known Member

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    Just got home, mod time!

    New Grill WhatsApp Image 2020-08-14 at 20.47.45.jpeg
     
  9. Iron1

    Iron1 Well-Known Member

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    Where did you get the grill - I'm looking at a 22 and it has the old, ugly tweed grill on it.
     
  10. Filipe Soares

    Filipe Soares Well-Known Member

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    There´s a guy here that cuts this kind of grills for speakers. I measure the head and asked him to cut it. In the end the cost was like 10usd with the delivery costs.
     
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  11. Filipe Soares

    Filipe Soares Well-Known Member

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    Just out of curiosity. while the mods from bryce are not here, can I change the Bias from some 12AX7 for more gain???


    jca20h schematic.jpg


    I was thinking about changing R29 or R25 or R43 or R20 for something different so I can get more pre amp distortion.

    What are your thoughts @NewReligion ?
     
  12. jchrisf

    jchrisf Well-Known Member

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    You motivated me to get mine out again. I also put my speaker cab on the floor of my closet and it sounds much better. This 22H rocks! I want to get a 20H since it is not as complicated to mod. Here is mine.. it has a Mercury Magnet transformer and a choke. Not sure what other mods were done because I bought it from GC.:headbanger:
    [​IMG]
     
  13. South Park

    South Park Well-Known Member

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    The cathodes resisters look good for gain already . You might drop the grid stopper value to get more signal R 27 and increase R 13 to 470 k to dump less signal . That preamp look a lot like a 2204 the same mods might work
     

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