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Bryan 27th March 2004 02:26 AM

Bouncing Ground
Hi all,

I just scoped several sections of my PS. I can measure about 11mV AC at the last cap of my power supply, but this value fluctuates up and down considderably. My fluke measures between 7 and 15 mV, and every so often jumps to about 20mV.

When I use the scope, it seems that the ground is bouncing up and down, for lack of a better way to describe what I see.

The PS is hybrid tube rectifier-LCLC- feeding tube voltage regulator.

At the VR tube, I measure a steady 4.4mVAC on the Fluke, and on the scope it is flat/steady.

Any thoughts?

Sch3mat1c 27th March 2004 04:27 AM

11mV, pffbt, just ignore it. You don't have a phono input hooked up to that point do 'ya?


cogsncogs 27th March 2004 04:50 AM


I'd say that's normal power line (AC mains) fluctuation. Power supplied to our homes is not steady either in amplitude or frequency. The reason it's steady at the VR tube is because of it's regulation. It's especially apparent if you use direct coupling vs AC coupling at the vertical input on your scope.

Hope this helps.


Bryan 27th March 2004 01:14 PM


11mV, pffbt, just ignore it.
What does the pffbt mean here, I haven't come across this one yet...

Nope, no phone here.

I was thinking that the fluctuation may be from the mains. I guess it is nothing to worry about.

Next observation.... From the VR tube, I have 4.5mV into the Pimm BBMCCCS. On the outpu of the CCS, I have 4.8mV. Is this normal?



Sch3mat1c 27th March 2004 06:03 PM

Phhbbt = fffbbt sound made when one razzes some(one/thing) ;)


Bryan 27th March 2004 06:09 PM

Thanks for the clarification!

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