[Milsurplus] BC-347-A Interphone question

[Michael Hanz]

On 2/8/2019 8:03 PM, Hubert Miller wrote:
>
> I was looking at a new unissued, in original packing BC-347-A 
> interphone amplifier.
> Looking at the back side, I see in each of four corners, but not 
> rigorously in the same exact position for each corner, a wire-sized hole.
>
> The first time I noted this, on a used BC-347-A, I thought, aha, 
> someone wanted to run wires into it, for a ham hack.
>
> But this new one has the same.
>
> What are these holes about ? They are ungrommeted, so any wire 
> transiting would be abraded.
>

Moisture relief.  In a closed box that is not hermetically sealed, one 
that experiences external temperature and humidity changes over a 24 
hour period, you need to have some way to "level" the humidity inside 
the box.  Failure to do so means that condensed water inside the box 
keeps increasing over time.  There are numerous tech bulletins issued 
about drilling such holes for aircraft control boxes and the like.

         73,
-Mike KC4TOS


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