Grounding Champ 5F1

Discussion in 'Amp Central Station' started by conner, Mar 26, 2004.

  1. conner

    conner NEW MEMBER!

    Posts:
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    Joined:
    Sep 17, 2003
    Hi everyone,

    I am currently working on a Champ 5F1 kit supplied by Marsh Amps. This
    is my first amp project and I'd really appreciate some comments on proper
    grounding. I'm not concerned with authenticity too much (though it would
    be interesting how Fender grounded their original).

    My focus is definitely on reduced hum. I am installing the mods Mike Marsh
    (and others) suggested: virtual center tap to cut down filament hum and using
    shielded wires on input jacks, volume control, and first grid of the preamp.

    Mike Marsh suggested I run a ground buss from the leftmost tang of the volume
    pot to the chassis grounded tangs of the input jacks to one of the mounting
    screws of the preamp tube.
    Do I need to solder anything directly to the chassis? I've heard you need a higher
    powered iron for this.

    Do I simply run all my grounds to this buss?

    Can I use a heavy gauge copper wire for the buss? Are there better alternatives?

    I heard it is a good idea to connect the main filter cap (16uF-450) to the screen
    supply cap (8uF-450) [Is this the correct term?] before running to the chassis
    ground.

    I also heard you should connect the two cathode resistors (1kOhm) and the preamp
    filter cap [the second 8uF-450] before running a common line to ground.

    Comments?

    What do I do with the other ground connections? The layout is not very clear on
    this. Specifically, how do I best wire the following ground connections:

    - the cap off the fuse
    - the virtual center tap on the filament supply
    - the Red/Yellow lead off the power tranny
    - the faraday shield (Orange) off the power tranny
    - the center tap off the 12Ax7 (pin 9)
    - pin 1 on the 6V6 (not important on the 6V6GT but I'd still prefer a proper
    connection in case I ever use a 6V6 (metal type))
    - the green wire from the power cord
    - the speaker output jack
    - the Black wire off the output transformer
    - the shielding on the shielded wires mentioned above
    - anything else I'm missing

    One final question:

    Does it make sense to twist any wires except the filament supply? For example the
    other leads going from the power transformer to the rectifier, or the speaker
    connection?
    Could twisting be a BAD idea, or is it immaterial in other cases?


    Thanks a lot for your input!

    Eric
     
  2. Rick S

    Rick S Tele-Meister

    Posts:
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    Joined:
    Nov 12, 2003
    Location:
    Tulsa, OK
    That's a lotta questions Eric! :lol: , I'll see what I can do briefly here and if I can be of further help, email me at OKRick at aol dot com.

    "I also heard you should connect the two cathode resistors (1kOhm) and the preamp"

    No, use 100 ohm.

    "- the cap off the fuse"

    Don't install that cap. With your "3 prong" power cord W/ground it serves no purpose.

    "- the virtual center tap on the filament supply "

    Most often, people will install the resistors on the terminals of the pilot lamp, and bend the leads to be grounded around the back of the lamp assy. and solder them directly to the flat back side of the lamp assy., assuming an original type lamp.

    "- the Red/Yellow lead off the power tranny "

    Install a solder lug under one of the power transformer mounting nuts, and solder it there.

    "- the faraday shield (Orange) off the power tranny "

    Same spot as the Red/Yellow above.

    "- the center tap off the 12Ax7 (pin 9)"

    Pin 9 is a filament. You will be putting a filament wire there, don't ground it.

    "- pin 1 on the 6V6 (not important on the 6V6GT but I'd still prefer a proper
    connection in case I ever use a 6V6 (metal type))"

    Kinda depends on the tube socket used. Some sockets have ground lugs on the socket flange, some sockets have pins long enough to just bend over and solder to the flange. Whatever, just make the shortest connection directly to ground from that pin.

    "- the green wire from the power cord"

    Install another solder lug under a different transformer nut from the one above. It can be soldered directly to the left chassis side, if you have the experience and iron necessary to do it properly. Standards require this to have it's own separate ground point, and it should be very secure. Most important ground you will be making.

    "- the speaker output jack "

    Will ground itself when installed.

    "- the Black wire off the output transformer"

    To the ground lug of the speaker jack.

    "- the shielding on the shielded wires mentioned above
    - anything else I'm missing "

    You didn't mention what you plan to use shielded cable on.

    "Does it make sense to twist any wires except the filament supply? For example the
    other leads going from the power transformer to the rectifier, or the speaker
    connection?
    Could twisting be a BAD idea, or is it immaterial in other cases? "

    Twist all your filament leads, including the rectifier filament leads, and the high voltage leads (red) to the rectifier, nothing else.


    Mike Marsh suggested I run a ground buss from the leftmost tang of the volume
    pot to the chassis grounded tangs of the input jacks to one of the mounting
    screws of the preamp tube.
    Do I need to solder anything directly to the chassis? I've heard you need a higher
    powered iron for this.

    Well, the original amps used a brass plate that installs under the input jacks and volume pot for a ground buss. Obviously, you didn't get one of these with your kit. My best advice would be to get one, and solder your grounds from the board to it, as was done on the original amps. You can buy one from Weber VST. On your Fender layout, all the leads from the board with the little ground arrows solder to the brass plate, and yes, a stout iron, minimum 80 watt, is necessary. I suppose you can probably run all your grounds from the board and volume pot to an input jack ground lug, but I think I would probably run the plate/screen filter ground back to the power transformer. I disagree with running a lead to the preamp socket, unless you are using isolated input jacks.
    I really think using Leo's method of the brass plate would keep you out of trouble. You can tinker with experimental grounding after you get more experience.
    Good luck, you'll get it runnin'
    Rick S
     
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