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

[Peter Bertini]

I believe the bypass caps are there to reduce "tuneable" hum
problems in those old receivers, more than being noise filters.
If you find you don't need them, leave them off. But if some
you begin hearing hum on stations that are tuned in, the lack
of bypassing is probably the problem.

Pete k1zjh



On Mon, Dec 13, 2010 at 1:03 AM, Glen Zook <gzook at yahoo.com> wrote:

> 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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