2204 circuit at lower output build

Discussion in 'Building the Classics' started by william vogel, Oct 16, 2021.

  1. william vogel

    william vogel Well-Known Member Gold Supporting Member

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    Just finished wiring it up. Makes 40 watts clean rms, 69 watts full power. This is my first 2204 circuit and first time running this circuit on a scope. The preamp definitely distorts and is completely different than a Plexi. I’ll get to play it tomorrow. Almost forgot, it idles at 410 volts and sags down to 364 at full power. It’s got Groove Tubes EL34M in it right now along with an Amperex Bugle Boy in V1, a Tungsram in V2 and a Telefunken ribbed plate in V3.
     
  2. neikeel

    neikeel Well-Known Member

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    Looks good, a real Vintage/Modern!!

    What preamp voltages are you getting using that PT and a single 8k2 dropper (normally expect a couple of droppers 8k2/8k2 or 10k/8k2 for a 2204, particularly if looking for the distortion to come in early, i.e. slightly less headroom?
     
  3. william vogel

    william vogel Well-Known Member Gold Supporting Member

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  4. neikeel

    neikeel Well-Known Member

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    Those voltages are quite a bit higher than a stock late 70s JMP 2204 (but then they had <400v rectified).
    I guess it depends on what you are looking for in tone?
     
  5. william vogel

    william vogel Well-Known Member Gold Supporting Member

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    Not to contest with you about the resistors but I haven’t found a schematic that shows the two dropping resistors after the choke on any 2204 schematics. I did see one with the lower DC voltage from the power transformer. This amp has enormous amounts of preamp distortion and sustain compared to my early Plexi circuits. Even at 40 watts it’s very powerful feeling. I’m still getting accustomed to it. I played it earlier this morning and am quite impressed with it. It has a good bit of bite with the 1nF bypass cap on the volume pot and it has plenty of bottom end. This circuit almost allows me to forget my boost, overdrive and distortion pedals.
     
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  6. william vogel

    william vogel Well-Known Member Gold Supporting Member

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    I just played it again. Finally cranked up the master. I cannot imagine having a 2203 100 watt. This little 40 watt amp is so in your face. This morning when I played it I had the master on 3 then 4 and the preamp volume on 6, 7, 8, 10 and thought I was pushing the output section into breakup. I was mistaken. I think I’ve found something here. I’m going to post a voltage chart for where everything is at when putting out full clean rms output and at full power. The 500 ohm choke really makes the voltages move around. This amp is soo reactive to pick attack, it just breaths as it’s played.
     
  7. william vogel

    william vogel Well-Known Member Gold Supporting Member

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  8. william vogel

    william vogel Well-Known Member Gold Supporting Member

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    Here’s my full voltage chart and transformer information
     
    Last edited: Oct 31, 2021
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