Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Need feedback on this basic grounding schema

  1. Dec 13, 2016 #1
    Hi guys,

    I am trying to find the best way to lay out a grounding system for a typical tube amp.


    I had in mind to place the filter caps along the HT rail. I can use either axial or radial caps. The issue with the radial caps is they tend to be too big in diameter.I am trying to get to some general design for the placement or ground wires/buss. Something that reduce noise to a minimum. Assume AC heaters with twisted wire and perhaps also covered with a braided shield.

    Need ideas.



    EDIT: sorry I have the connections to the grids drawn incorrectly. Tip of the input jack goes to V1 Pin 2 and the center of the volume control pot goes to V1 Pin 7
    Last edited: Dec 13, 2016
  2. jcsd
  3. Dec 13, 2016 #2
    Here is a typical layout and schematic for a typical Fender style amp. Perhaps it will make the drawing above easier to understand.



  4. Dec 13, 2016 #3


    User Avatar
    Science Advisor

    Keep the filter caps as close as possible to the HT rectifier. You need minimum resistance between the rectifiers and the caps. You do not want twice mains frequency current spikes travelling along the HT lines.
    Place a toroid over the two wires feeding the last reservoir cap. The last cap then provides HT and the ground connection to circuits.
    The first cap(s) have the centre tap of HT windings only, no chassis connection except through torroid wires.
  5. Dec 13, 2016 #4
    Thanks Baluncore,
    Here is a experimental amp built along the lines of the Bright Switch Mid Pot Layout above. The filter caps in this example are close to the rectifier tube and not along the board. The resistance from the rectifier to the first filter cap measures .03 ohms. As it goes through the standby switch I assume some of the resistance occurs there. The HT ground wire from the transformer is connected to the star ground which you can not see in the video. Directly from the star ground is a wire connected to the negative side of all the filter caps. All these connecting wires are 18 gauge solid copper wire.

    Perhaps looking at this video you can give me a better description of what you think I should do.



    EDIT: Just so you know, There is not an excessive amount of hum or hiss in this amp...more than I would like nonetheless. The real problems occur as the amps have higher gain and higher wattage.
    This one is only 20 watts or less.
  6. Dec 14, 2016 #5
    With a change to the input jack ground the amp is dead silent now. On to the high gain amp next.

    Thanks for all the ideas and links as they were very useful. I think I am starting to get a handle on the grounding issues.


Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted