[R-390] Line input filter safety diatribe

[Perry Sandeen]

Gentlemen, Gentlemen, Gentlemen,

WARNING: Ultra-long SAFETY Diatribe.

When I wrote before requesting people turn down their pacemakers to await the next nicker-twister
I didn’t realize it would be me who got them wound up again!  Therefore, I gladly shoulder my
responsibility to offer this carefully and scientific reasoned diatribe for the edification of all
to follow my advice before SOMEONE GETS KILLED.

Wrote: we MAY HAVE NO CHOICE but to run  a separate circuit for OUR R-3XXs! and: So wholesale
changing the filtering is NOT the  proper method of "FIXING".  IF the filter is up to spec, leave
it in  place to do ITS JOB.

Three Strikes!  
Strike one: Running a separate circuit requires a permit and still has to meet local specs.  If it
is in a defined "wet location" you will void your homeowners insurance if it isn’t GFCI protected
and something goes wrong.

Strike Two: The modern filters beat any of the original specs by a country mile. A standard unit
can have 250 micro-amps leakage and 50 to 75 db attenuation from 1-30 MHz..

Strike Three:  It is beyond reason to use a part that can kill you when the better replacement
part won’t.

Wrote: question... Why are people plugging their boatanchors into GFCI circuits and the only
circuits in my house with GFCI breakers are in the bathroom and outside outlets.

Answer:  1) That may be the only choice they have. 2) If there are no GFCI’s in your kitchen it
doesn’t meet current (pun intended) code requirements.

Wrote: This radio and this entire subject isn't for the beginner nor is this manual to be
considered a basic primer to the subject.

This is true in the theoretical. In the practical world we all get stuff we aren’t experts in. 
It’s part of the BA addiction.  See the question below from a licensed  Ham.  The filter is a
known "gotcha" as is the Mechanical Filter blocking capacitor.  The difference is that this
"gotcha" can kill you and there is a perfectly safe better alternative.  I know lots about
electrical safety as I fixed medical equipment for 25 years.  It was part of my everyday work. 
Everybody starts from ground zero.  I could only use a "Smith Chart Calculator" for a frizzbe,
others can design solid state UHF amplifiers with it. We all learn faster and safer when we get
"Elmer" advice.

Wrote: I had to assume that the house wiring was correct and up to date.

A fair assumption considering the scope of your advice was covering the only the radio and you did
this well.  Considering the feedback we are getting on the list about wiring problems members are
encountering we may need to add some comments in R3 cautioning people about verifying their
electrical systems 

Wrote: (off line to me) I have  a 390A with the leakage problem. Could you please give me an idea
of what computer type circuit you are referring to, or how I could get one ?  WXXX.

Glad you asked.  But first an explanation of why.  Modern electronic equipment is designed to have
a two fault failure system before posing a hazard.  This means for example , if you lose your
green ground chassis connection the ungrounded equipment  does not have enough leakage current to
cause harm even if the polarity is reversed.  Due to the design criteria this wasn’t stated and
from a logical use planned for the equipment wasn’t necessary.  

With  the stock R390A filter, you have without GFCI circuits, a one fault system.  If you lose
your ground, it can kill you.  With GFCI wiring it will trip the GFCI breaker tempting "fudging"
or "moonlight engineering" work arounds  that  usually range from ill-advised to "death looking
for a place to occur."

There is nothing special in filtering terms about the stock R390 filter.  In fact, it is less
effective that what you can easily acquire today.  There are two types of filters generally
available.  The ones called "Medical Grade"  but they are way over-kill.  A standard unit can have
250 micro-amps leakage and 50 to 75 db attenuation from 1-30 MHz. 

The easy way.
Obtain a defective computer power supply.  PC shops will usually give you one or charge a couple
of bucks.  Remove the IEC power input connector.  It should be about 3 inches long if it is a
filtered plug.  (A 99.99% certainty.)  It may also have an additional EMI filter soldered to the
leads.  This is a good bonus. Remove the power input connector.  File the chassis a bit and mount
it in the hole.  Disconnect the old filter AND THROW IT AWAY.  Wire in new filter.  Enjoy your
safe radio.

A bit more difficult.
Use any major parts suppliers catalog, paper or on-line.  Go to the line input filter section. 
"Corcom/Tyco" is a major brand.  Look at the rated leakage specs for  the filters.  Either use one
with an IEC power connector or you can buy them with solder lugs.  There are a bizillon types. 
All you need is a 3 amp unit.  Pick the performance you want. Buy.  Install.  THROW AWAY THE
ORIGINAL FILTER.  Enjoy your safe radio.

I blatantly DO NOT apologize for using this much bandwidth.  Keeping people on the radar screen is
far too important.  Live Long! Stay Healthy! Regards, Perrier



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