[Hallicrafters] AC Bypass Caps in SX-111 MK 1.

[Carl]

Id certainly replace them as its very cheap insurance against a particularly 
nasty line spike taking out the transformer or rectifier tube. That scenario 
is a lot more possible today than in the days of old.

The engineers put them in there for a reason and I keep wondering why self 
appointed experts with insufficient engineering backround keep trying to 
second guess them.

Carl
KM1H




----- Original Message ----- 
From: "Glen Zook" <gzook at yahoo.com>
To: "Mark K3MSB" <mark.k3msb at gmail.com>; "List Hallicrafters" 
<hallicrafters at mailman.qth.net>; "Mike Everette" <radiocompass at yahoo.com>
Sent: Monday, December 13, 2010 1:03 AM
Subject: Re: [Hallicrafters] AC Bypass Caps in SX-111 MK 1.


Actually, it really isn't leakage.  Capacitors are supposed to pass AC and 
block DC.  Therefore, any radio with those capacitors is going to have 1/2 
of the mains voltage on the chassis.  Of course, with 3 wire cords that 
voltage is grounded out.  It is the same with 2 wire cords when the chassis 
is grounded.  That is one of the reasons that the older equipment always had 
a ground terminal (except for AC/DC which often did not).

Now when the capacitor does fail, then the full mains voltage and current 
then can definitely be on the chassis.  Otherwise, the current is limited 
through the capacitor because of the relatively high impedance inherent to 
the value.

These days it is questionable as to whether or not to install line bypass 
capacitors, especially in receivers.  In my opinion, leaving them out isn't 
going to hurt anything.

Glen, K9STH

Website:  http://k9sth.com


--- On Sun, 12/12/10, Mike Everette <radiocompass at yahoo.com> wrote:

I'm sure some folks will disagree with me... but I would recommend that you 
not sweat those line bypass caps. In fact, LEAVE THEM THE HECK OUT.

If they start to leak much at all, you are going to have AC voltage on the 
chassis. I've seen radios with between 30 and 60 volts AC on them for this 
reason. That's enough to give you one serious jolt. And yes, this was due to 
line bypass capacitor leakage... not leakage in the power transformer. In 
all my experience, which includes ham radio, commercial two-way, avionics, 
and broadcast engineering, I have seen only two power transformers develop 
primary-to-frame leakage; but PLENTY of leaky line bypass caps. I damn near 
got killed once by a background-music system PA amplifier with a hot chassis 
from a leaky cap, when the back of my head touched that chassi as I was 
reaching my bare and sweaty arm behind a HVAC duct to fish out a speaker 
lead. Sha-ZAAAAAAM! As a result, the very first thing I do when a "new" 
radio or any other device comes into my life is to make REAL sure to take 
the things out of it!

I remain unconvinced regarding the benefits of having these capacitors in 
the radio at all.... except to a funeral director.



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