[R-390] Z503 Replacement

[Graham Baxter]

I had an open circuit Z503 in an EAC R390A. I gently heated the
ferrite cup and managed to pull it off the former. The coil, which if
I recall correctly was wound with the type of fine litz you often see
on a ferrite rod long wave coil, had gone rotten.

I cut off the pie which was wave-wound. I made a pair of cardboard
cheeks and glued them to the former. I then pile wound some new wire
of a similar but not necessarily identical type until I had achieved
roughly the same dimensions. I varnished the winding, and once the
varnish had gone off I picked out the carboard cheeks. On reassembly,
it peaked up within range of the slug and has now been working for
several years.

So there is hope!

Graham Baxter

G8OAD

On 4 April 2011 18:26, Tisha Hayes <tisha.hayes at gmail.com> wrote:
> Randy makes a great point. None of the constituent components that make up a
> coil form have the same coefficients of expansion due to heating/ cooling.
> If you mechanically stress any wire it will eventually "cold work" at a
> stress point and fracture.
>
> It is not as if these receivers have never been exposed to vibration,
> dropping, hot environments or transient voltages. There have been problems
> in the past with the power and audio transformers where the wax/asphalt/tar
> hardens and eventually the transformer fails.
>
> We are all doing things to pieces of equipment that are well beyond their
> design lives. Obscure failure mechanisms will begin to pop up. Another
> example of that is the gooey mess that the foam inside of the mechanical
> filters turns into.
>
> Then again, sometimes "stuff" happens. The particular failure of this one
> inductor does not seem to be a widespread problem that we all are
> experiencing. If we dedicated as much effort into the analysis of every
> single component in the receiver as we have to Z503 then we have at least
> another 30 years of discussions to hold.
>
> It was interesting to see how folks figured out the L, C and Q values of
> Z503. We have even bounced around the ideas of why the Q should be where it
> is at. All great discussions but at the end of the day, 85% of us who may
> have a failure of Z503 will just pull one off of a junker IF deck that are
> flooding the auction sites.
>
> --
> Ms. Tisha Hayes/ AA4HA
> -
> *“If toast always lands butter-side down, and cats always land on their
> feet, what happens if you strap toast on the back of a cat and drop it?”
> Steven Wright
>
> ***
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