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From: Cursitor Doom <cd@notformail.com>
Newsgroups: sci.electronics.repair,sci.electronics.design
Subject: Re: PSU Ripple Update
Date: Sun, 17 Mar 2024 19:43:26 +0000
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On Sun, 17 Mar 2024 11:33:12 -0700, John Larkin <jl@997PotHill.com>
wrote:

>On Sun, 17 Mar 2024 17:48:07 +0000, Cursitor Doom <cd@notformail.com>
>wrote:
>
>>Gentlemen (and others)
>>
>>I only get a few spare minutes a week to look into this, hence this
>>update. Hopefully my latest finding might ring a bell for some of you
>>and assist in pinpointing the fault with this (linear) PSU.
>>So, I've carried out a few more tests and discovered that there is a
>>total absence of ripple on the storage caps when all the downstream
>>circuitry has been disconnected. So it's totally fine with no load.
>>However, as I re-connect all those downstream circuits, the ripple
>>commences and the more connectors I re-attach, the worse it gets. This
>>is a screen shot showing over a volt of ripple at only about 66% of
>>the full supply voltage applied:
>>
>>https://disk.yandex.com/i/vgxfpXgNp-F4Yg
>>
>>Now I did check to see if there was anything downstream which had
>>shorted or gone low-resistance which could possibly account for this,
>>but found nothing amiss. So the question is:
>>What could cause ripple to arise when even very light loads are
>>applied to the output of a pretty substantial linear PSU?
>>
>>BTW, the bridge rectifiers were fine and have been exonerated from any
>>culpability in this fault.
>
>Is there actually a fault? Transformer-rectifier supplies have ripple.

Yes, it's a fault alright. The ripple is superimposed on the output of
the RF generator; it's impossible to ignore.