Bob May wrote:
I'd grab my Dremel with a small dentist bit in it and start cleaning out
around the stud so that I could get at it. Epoxy later can fill the hole.
Be carefull as the binding post may be soldered to a printed circuit board
rather than a wire.
Then, after finding the wire, solder to the wire a new binding post. The
binding post is probalby a 5 way post that Radio Shack sells.
Short of that, you probbaly don't have enough meat inside to do a good job
of drilling and tapping a new hole as just inside there is usually a smaller
section where the soldering is actually done onto the post.
Don't bother with the conductive epoxies as their conductivity isn't good
enough to do a good job of conducting the current that the speaker will be
using. Take the number of watts that the speaker is rated for and divide by
8 for the amps of current that the speaker uses and you may be supprised at
how much current that the speaker uses and consider that you go and buy low
resistance wire just to make the speaker sound good. Any resistance in the
path decreases the volume and increases the resonant points of the speaker
which makes it sound bad.
I was about to strongly suggest he use conductive epoxy to join the
broken parts when I read your comment. Conductive epoxy has saved my
chops quite a few times when I didn't dare apply soldering heat to
someting, and once when the magnet wire I needed to reconnect turned out
to be made from aluminum. (I just reminded myself of the Korean war era
when I used to run into TV deflection yokes and power transformers wound
with enameled coated aluminum magnet wire, because copper was needed for
the war effort.)
Conductive epoxy is expensive, but I've had the same two little tubes of
the stuff sitting in the kitchen freezer for at least a dozen years now,
and usually just "a little dab will do ya".. It still works as good as
it did when I bought it after about ten minutes warming up the two tubes
in my pants pocket.
Before packing it in I Googled up some specs on conductive epoxies and
found their volume resistivities are claimed to be around .001 ohm-cm.
Now, copper is about 1000 times lower in resistance than that so at
first what you said about adding too much series resistance in the
speaker circuit almost scared me off.
But, I don't give up that easily, and decided to work it out. Suppose
the broken post is about 5mm in diameter and he can butt join the two
broken ends together with a layer of conductive epoxy averaging say
0.5mm thick.
If I just did the math right the series resistance of that layer of
epoxy will be only about 0.25 milliohm.
Number 12 copper wire has a resistance of about 2 milliohms per foot, so
it seems like that layer of conductive epoxy will have no more effect
than adding another couple of inches of that kind of wire to the speaker
leads, hardly a major worry, 'eh?
I don't claim to be an expert on this stuff, and I never even played one
on TV, and maybe there's some "contact resistance" factor or something
else I don't know of that sneaks up to grab you at the epoxy-metal
interface. But if there isn't, than I don't see why conductive epoxy
won't do the job for him safely, particularly if he can buttress and
protect the part he's joining back on so that it's not likely to bust
off again.
If the OP can satisfy himself that it's safe to drill a hole a short
distance down the center of the remaining piece and drills a similar
hole in the broken off piece, then he could splint the epoxy joint with
a short piece clipped off a No.4 brass machine screw and add strength.
Just my .02,
Jeff
--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
"Truth exists; only falsehood has to be invented."
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