Power filter bigger caps causing hum?

[JoeM]

I'm not sure how you wired these in. There are other caps for the later stages on the filter PCB, so I think the best place for the new caps would be to just replace the other ones. And, yes, where you connect the grounds for the filter caps is important for lowest noise.

[Steve Conner]

Yes, there's your problem, bad choice of ground. The new caps should connect right across the terminals of the old ones.

[Bruce / Mission Amps]

Find in your schematic and or layout where the high voltage secondary center tap of the power transformer is grounded and or connected to the original filter caps... (it's usually a red/yellow wire but you'll have to check).
This is the exact spot you'll need to have your negative lead of the Hi-V cap stack connected.

[Stevie B]

Find in your schematic and or layout where the high voltage secondary center tap of the power transformer is grounded and or connected to the original filter caps... (it's usually a red/yellow wire but you'll have to check).
This is the exact spot you'll need to have your negative lead of the Hi-V cap stack connected.

Bruce,
YES!!
You were right.
Can you explain why this works?

I originally grounded the caps where the power cord grounds to the chassis.
It even has a little sticker that shows the ground symbol.

Thank you

PROBLEM SOLVED thanks to Bruce.

[tubeswell]

Bruce,
YES!!
You were right.
Can you explain why this works?

Read Merlin's grounding article on the Valve Wizard site. Basically you want to ground the parts of those parts of the circuit that get their power supply from a certain filter cap, to have their ground return returning at exactly the same ground return point as that same filter cap.

The filter caps are all madly trying to shunt any AC that is in the power supply, to ground. They do this in order to keep the power supply voltage constant. But filter caps are not perfect electrical devices in this regard, and there is always some residual micro-wobble voltage on the ground side of the filter cap. If the ground return part of the circuit that is being supplied from the power supply end of the cap is grounded with the ground return of the same cap, it keeps this ground-side micro-wobble voltage to a minimum. If you don't do this, then the ground return path between wherever else you do ground that part of the circuit and the ground return of the relevant filter cap will cross these different micro-wiggle voltages and this will feed-back into the signal as hum. In this regard, the ground return path is in-itself also a conductor with a certain resistance between any two different ground return points, and when you have different ground return currents at different points within the ground return, then you will get a voltage drop between those points. What's more, the different parts of the circuit are all returning different amounts of current through the ground return. Having different filter caps sitting at different points in the ground return path returning different currents, means you get a voltage drop between the filter cap ground returns. So if you mix up the other ground returns by returning them to other filter cap ground returns, you will shunt this voltage drop back into the power supply through those other parts of the circuit, which causes hum in the signal path.

[Jazz P Bass]

Very well stated mate.
Thanks.