[Boatanchors] X-Y Safety Capacitors -Advises Sought

[Rob Atkinson]

Hi,

I have never put those in any power supply I was building, but I have
found them in equipment here from time to time.  I think they are
unnecessary in linear transformer power supplies because the
transformer is a barrier to RF on the AC line.  I would consider them
for a transformerless power supply or in a switch mode power
supply--maybe.  I need to think about that last one, but definitely in
a supply that rectifies right off the AC line.

73
Rob
K5UJ

On Wed, Aug 27, 2025 at 2:38 PM Scott Freeberg WA9WFA via Boatanchors
<boatanchors at mailman.qth.net> wrote:
>
> I'm building a power supply for my HB-67 single/dual conversion
> superheterodyne receiver from the 1967 - 1969 ARRL Handbook.  Excellent
> receiver and works well from the ole Heathkit SP-17A.  I'm building a stand
> alone power supply for it now.  For the first time, I'm using a toroidal
> power transformer and 5H choke.  Interesting..
>
>
>
> Do you guys put in X-Y so called "safety capacitors" on the AC line?  I've
> read where the Y capacitors are used on AC for the purpose of reducing RFI.
> Is this so?  I've never used them before.  I only ask because I'm all for
> reducing RF noise in a receiver, and I have the DigiKey order page open.
> Believe it or not but I didn't have a single 1N4007 in the shack. Thanks.
>
>
>
> 73, Scott WA9WFA
>