Grounding Question

[EdStiles]

I'm rebuilding an original ST-35 and have replaced the boards with blanks that I stuffed. I also purchased a Chong ST-35 cap board and a shielded C354 choke. Have everything mounted, and have isolated the cap board from the chassis with nylon screws and spacers.

My question involves the grounding: I am planning on using a single point (the original ground) on the chassis to connect a "star" ground but not sure about the best way to connect the power transformer center tap and ground the cap board.

Option 1 would be to run both to the star ground.

Option 2 would be to run the center tap to the cap board, then run a heavy (16-18 ga) wire from the cap board to the "star" ground.

CChong suggests connecting the center tap to the cap board, then grounding thru the mounting hardware.

Any thoughts on which would be the best solution?

Thanks,

Ed

[erichayes]

Hi Ed,

Whenever possible, it's best to run your ground leads to a single chassis point, preferably as close to the input jack as you can get it. If you have to use a ground bus, which is not a bad thing, try to keep your high current grounds (PT center tap, filter caps etc) "starred" at one point on the bus bar (I use 10 ga bare grounding wire from my local Ace Hardware), and the end of the bus bar connected to the chassis ground point.

The idea is to connect as many ground leads to as few points as possible. Using the chassis, especially if it's cold rolled steel, as a ground plane is the worst of all scenarios due to high resistance mechanical connections between the ground lugs and the chassis. Aluminum chassis aren't much better, as there's galvanic action between the steel hardware and the chassis that can also raise Hell with hum suppression.