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My new tubed toy + tech question...

Discussion in 'Amps and Cabs [BG]' started by Rickenbackerman, Dec 24, 2001.

  1. Rickenbackerman


    Apr 17, 2001
    Laurel MD
    Sound City 200 plus! Pics at:


    BIG ass partridge transformers, recent cap job, new power tubes... got it CHEAP. Awesome build quality, too - look at the wiring! Only tried it at low low volume, but it sounds REAL nice. Alongside my '72 SVT and Mesa 400+, I've got a decent arsenal now! :) Anybody else have one of these?

    The tech part - how do I wire up a grounded power cord to it? Do I just wire the ground to the chassis and that's it? Gotta get rid of that 2-prong cord of death...
  2. Cool amp, man. I covet your amp. :D

    Remove the old power cord, then replace it with 3-conductor power cord and plug. Make sure your cord is still properly grommeted in place - shouldn't be able to twist the cord on the outside and have it move much on the inside, you know, common sense.

    Hook black and white wires where the old 2-wire cord connected (preferably so the black wire is going to the fused side of the circuit), and hook green wire directly to chassis metal with a 8-32 screw, internal tooth lock washer, and nut. You can use a crimp on ring terminal on the green wire end to mate with the 8-32 screw, and I usually fill the crimps with solder after crimping just for better connection. Don't mess with any of the rest of the amp.

    That's it. Now your chassis has an alternate safety return path to AC neutral, IF the outlet is wired correctly. Any failure of any insulation on the 120VAC side of the circuit will give a low-resistance path back to 120VAC neutral, and the circuit breaker will blow.

    I forgot to check where you live, Europe uses blue=neutral, brown=hot, and green/yellow=ground. US uses black=hot, white=neutral, and green=ground

    stolen graphic:

  3. Rickenbackerman


    Apr 17, 2001
    Laurel MD
    Thanks Chris! I found this link:


    and they mention removing the ground switch and associated capacitor as found on most vintage amps. My amp DOES have this feature. Essentially, with a two prong cord, the ground switch just floats the ground from one side to the other through a cap. But with a grounded cord, I don't need it. Does that sound right?

    If I leave the ground switch in there, isn't there a possibility of having a dead short if the switch is set to the position where the floating ground is switched to the hot side?
  4. I like the look.. sort of like a Marshall with a different faceplate.
  5. Rickenbackerman


    Apr 17, 2001
    Laurel MD
    It doesn't sound like a Marshall though! Quite the opposite, actually. It's got active tone controls and is LOUD and CLEAN.
  6. WOW!

    *Vercua Salt voice*

    "Daddy!!!I want a Sound City tube amp NOOWWW!!!!" *stomping foot*

    *Mr. Salt voice*

    "Here then Wonka.....er Rickenbackerman,how much for that sound city tube amp?"

    *Willy Wonka/Rickenbcker voice*

    "Oh,I`m sorry....it`s not for sale"

    :D :p

    Killer amp Rman!
  7. Yes, the ground or "Polarity" switch is unnecessary once you add the safety-ground wire to the power cord. You can leave it in the amp, just disconnect the wires running to it and the "death cap". That way the amp still looks the same.

    Like you say, if you leave it in, and it is flipped so there is 120VAC across the "death-cap", a little bit of current will flow through the "death-cap" and down the ground lead. Not a lot though, a 0.047uF cap at 60Hz has an impedance of 1/(2*pi*60*0.000000047) = 57K, 120/57,000 = 2mA. Not a lot of current. And the cap is rated at 630V usually, so 120V is not a problem.

    Still, you can disconnect it from the circuit.

  8. Rickenbackerman


    Apr 17, 2001
    Laurel MD
    Chris, thanks a million for clarifying bro.
    I rewired the 200+, as well as my B-15 last nite.
    It's nice to know I'm not going to get killed by my amps now. :)
  9. Rickenbackerman


    Apr 17, 2001
    Laurel MD
    Techs may be interested - just thought I'd bump this thread back to the top, as I've done some mega work to this amp.

    It wasn't working well at high volumes - the distorted tone was very harsh; almost solid-state like. After talking to some sound city experts on the plexi palace board, I came to the conclusion that it's the preamp. These amps came with some weird active preamp that (when turned up) introduces strange distortion as a result of hacking the frequency spectrum up into different bands to boost. I think. anyway...

    What did I do? I turned it into a Hiwatt. :) Ordered some G10 board and turrets from Hoffman amps, followed schematics and layouts by a super guy named Mark H (mhuss.com), and had at it. I didn't touch the power supply or output section, as the amp had been to Pete Cage for a going-through and was 100% healthy. It's making 220 clean watts out of a set of poorly-matched Svet 6550's. With KT90's, I wonder if I could get over 300W? That could be fun. This amp has a B+ of 760V!

    This is my first real tube amp project, and I think it came out pretty good. I've got a pic of the conversion here:


    The only thing is, it's REALLY bright. I'm trying to talk Gibsongeek into opening up his early DR201 to find out what the optional Hiwatt bass-preamp mod entails.

    Oh, it's loud now too. A/B-ed with my SVT into my 8x10, it's almost as loud, but is REALLY dirty at SVT-like volumes.


    AMJBASS Supporting Member

    Jan 8, 2002
    Ontario, Canada
    That is a really nice looking amp! Looks like an old Marshall JMP. Very cool! Can't beat tubes.
  11. Rickenbackerman


    Apr 17, 2001
    Laurel MD
    Thanks man! But trust me, this thing makes a 100W Marshall look like a toy. It weighs 65 lbs and is MUCH bigger. :D

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