My first build! JCM800 2204

Discussion in 'Building the Classics' started by adew1, Nov 21, 2020.

  1. adew1

    adew1 Active Member

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    Hi all,

    Today was the magic day of plugging in the power cable and switching it on for the first time. To say I was nervous was an understatement. Amazingly, the house did not disappear in a flash of flame and smoke, just a little burst of light from the dim bulb limiter when flicking it off Standby.

    No bangs, no smoke, no drama. To say I am delighted is putting it mildly.

    I spent a while measuring the various voltages with no tubes, then put in the Preamp tubes and re-measured. Do the voltages look reasonable?
    [​IMG]

    Rectifier in voltage = 601Vac, rectifier out = 446Vdc.

    The amp was built from a Modulus Amplification kit (their MOD800 kit), with a few tweaks:
    1. Switchable bright cap
    2. Treble peaker reduced from 500pF to 330pF
    3. V1a cathode resistor = 8.2k

    I will be posting some build photos and adding more info about the build shortly.
     
    Last edited: Nov 22, 2020
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  2. neikeel

    neikeel Well-Known Member

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    Looks about right, time for a load and some tubes!
     
  3. adew1

    adew1 Active Member

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    Thanks, neikeel. :cheers:

    For us newbies, this stage of the build is the most nerve-wracking. Will report back soon... :)
     
  4. Gunner64

    Gunner64 Emotional Support Animal Gold Supporting Member

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    It doesn't matter how many you build...flipping that standby switch is a bit of a rush of nervous energy...:D
     
  5. adew1

    adew1 Active Member

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    Tubes loaded and all voltages measured again:

    [​IMG]

    However, no sound at all, not even a reassuring hiss through the speaker (I was using a dummy load for all testing up to now, hence just discovered this).

    Went around checking continuity on all signal wires, and all seemed good. Having said that, I was getting continuity between signal conductor and shield on the shielded wires to the Master and Preamp pots. Sure enough, some hamfisted soldering of the shield to the pot casings had melted the inner insulator sleeves, thus shorting out the signal. Duh!

    I really don't like working with RG-174 cable, it's so delicate and the insulation seems to have the melting point of chocolate. (Yes, I know, I probably need to get better at soldering delicate things, lol).

    After messing around replacing those two wires, I fired up the amp and once again no sound from the speaker. I twiddled the knobs and, as I could definitely here some scratchy noise when playing with the Resonance knob (no, this isn't an exact replica), then turned the Master to halfway and hooray - a touch of hiss. Grabbed the guitar, and hey presto "It's alive!"

    The only cab to hand was a 2x12 with Creambacks. First impressions - brighter and more brittle sounding than I was expecting. My complicated switchable bright caps don't make much difference, although I was playing at quite high volume. The Raw switch works great: switches between either normal TMB stack or a resistor between Mid pot and ground. I went with a 220k resistor, which adds a volume boost and increased mids, but not quite as much as I'm looking for. I'll play around clipping in some higher value resistors to get what I'm looking for.

    Overall, the amp is very quiet - much quieter than my JCM2000 DSL100 - Modulus' grounding scheme of only one signal ground giving a very low noise floor. There is a touch of mains hum, which I will investigate, but not excessive at all.

    I need to spend more time playing the amp with different guitars and speakers, but so far I'm very happy with my first build.

    Will post some photos later today.
     
  6. neikeel

    neikeel Well-Known Member

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    Well done.
    Which caps/resistors did you opt for?
    I think Michael sends JJ tubes as stock?
     
  7. South Park

    South Park Well-Known Member

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    Don’t feel bad I did the same thing on my 2204 so quiet I did not think it was working . When you get to certain point in a build you can power things up as you build it . So what is the next build
     
  8. adew1

    adew1 Active Member

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    Thanks!
    I went for carbon film resistors and Sozo caps. I changed a couple of values, so used some Vishay metal films I had lying around around in a couple of places. I also used Mallory 150s in a couple of spots.
    Yes, Michael supplied JJs as stock. They are not my favourites, but will do for now.

    Studying the schematic I drew up from Michael's layout diagram (he doesn't publish a schematic, AFAIK), I think I have slightly screwed up my implementation of the Resonance control I added. It works, but I seem to have some DC on the pot, hence the scratchiness I mentioned earlier. I need to look at that again.
     
  9. adew1

    adew1 Active Member

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    Funny you should ask that. I have a large package from Valvestorm here with the parts for a 100w Master Volume. Yes, I know, crazy, but there is something about 100 watters that I can't resist. And I'm already thinking ahead to a JTM45... Yes, I think I need medication. :D:D:D
     
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  10. adew1

    adew1 Active Member

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    A few photos:

    [​IMG]

    [​IMG]

    [​IMG]
     
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  11. ibmorjamn

    ibmorjamn Well-Known Member

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    Well done , I wish my first build looked that good ! However mine were scratch builds .
     
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  12. Travis398

    Travis398 Well-Known Member

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    Looks good, Nice and shiny. Are you putting an effects loop in?
     
  13. Im247frogs

    Im247frogs Well-Known Member

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    Really clean work buddy.
     
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  14. South Park

    South Park Well-Known Member

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    Yes 100 watts are off the charts . I just built a slo 50 clone that shakes the windows . I have a slo 100 I’m putting together right know. Thar is a point to point layout for that and you can use fender transformers and you can get the slo chassis you don’t need the Chanel switching. Not a simple build but it can be done some you should look in to it
     
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  15. adew1

    adew1 Active Member

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    Yes, a Metro Zero Loss FX loop. I'll put that in once I'm 100% happy with the work I've done so far.
     
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  16. adew1

    adew1 Active Member

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    Thanks! I'm not 100% happy with the lead dress around the main filter cans area, but the amp seems quiet enough so I don't intend to go back and redo it. I learnt a lot doing this first build and will definitely do a few things a little differently next time.
     
  17. proxy

    proxy Well-Known Member

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    That looks great... I hope you can get us some clips so we can hear it:applause:
     
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  18. coolidge56

    coolidge56 Well-Known Member Double Platinum Supporting Member

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    That blue/brownish twisted pair from your VAC in looks too close to the chassis/head shell nuts. Just saying. Otherwise very nice build!
     
  19. Chris-in-LA

    Chris-in-LA Well-Known Member

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    2204’s are among my favorite amps. Turn the treble and mids down to 2 or 3, gain up to 5 or 6, all bright and brittle should disappear. I also built 2 JTM45’s recently, also great sounding. The 2204’s are better for when you have to turn down in the house. The JTM45 is more touch sensitive and less compressed and works great when playing with others.
     
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  20. Chris-in-LA

    Chris-in-LA Well-Known Member

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    BTW, you have to use high heat when soldering to the pots, not your fault the wire insulation melted.
     

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