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Inside Those Bird
Slugs
| Did you ever end up with or do you now have a dead
Bird slug? No, not the kind you have in your shotgun but the
kind which fits inside the Bird Wattmeter series which makes them so
valuable. Have you ever wondered what was inside them?
Well, I had one which I purchased at a hamfest ("Is it working
OK?" "Sure, it is. I used it right before I headed |
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| down here to the hamfest.")
I foolishly believed the seller but once I tested it at home, I
realized that I had a dead slug. I have since found a way to
test them before paying the money and I'll be glad to share that
info later. |
In addition, I was always curious as to what was on the insides of
those little beasts. After all, what could be inside to make that
little thing worth so much money? Since mine was dead, and I had
little to lose, I opened it up to see. I will share with you the
inside story, and I now know why they are so dear to the pocketbook.
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I did not take this project lightly. I spent
long hours searching the Internet but was never able to find any
information on the slugs themselves, either pictures or text, to
describe what the folks in Cleveland placed inside those little gold
cylinders. I hope this article can save someone else some
search time if they attempt the same endeavor. |
First, to test a Bird slug (assuming that you are going to a hamfest),
take along a small VOM that has, at least, a resistance scale. If
the seller (assuming you are also buying at a hamfest) will allow you to
test it, place the VOM on a higher resistance scale (I used the 20K scale
on the little yellow $9 marvel I had). Hold the slug in one hand and
place one probe on the round shell of the slug while carefully touching
one of the small connection which is exposed on one side. Then
reverse the VOM leads. Test it just like you would test a diode --
you want continuity in one direction and an open connection the other
way. Then test the connection on the other side of the slug
the same way, expecting the same results. If you find
continuity, or a very low resistance, from the shell to a connection in
both directions, something is shorted in the slug. If you find no
continuity in either direction, something is open in the slug.
Either way will cause it not to work. On the one I had, I had no
continuity.
Over a period of months I would pick that slug up and try to twist,
poke, pull and generally try to see how to get inside it to see if
anything was obviously gone. It resisted my every
attempt. My wife would have said, "throw it away... it isn't any
good. Just forget the money that you wasted on it..........It's
gone!"
I don't think so. 'Course I really didn't tell her that I bought
a dud so she didn't actually say that. Finally, over a year
past the original purchase, I decided to take drastic steps. After
all, it's dead anyway ---- what can I hurt?
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Carefully examining the dead slug revealed that
someone had used some type of grinding tool on the face of the slug
on two sides. (I know, I know, I should have seen that
sooner......and especially before I bought it.....) The two
round grinding spots were within the arrow which seems to be on all
Bird slugs showing which direction it is to be turned.
One was directly within the arrow head and the other at the
opposite, tail side of the arrow. |
With my Dremel tool and several different bits and stones, I was able
to grind down past the aluminum disk which is the label, and pop the label
disk off. I regret that when this activity took place, I did not own
a digital camera so I have no actual pictures of the following
steps. Even though I now have a camera, I cannot bring myself to
re-enter the slug, just to get pictures. I will attempt to be, in
words, as descriptive as a camera would have been in pictures.
Once the label disk was off, it revealed a cavity in the center with a
single screw which was covered with a sealer to show whether it had been
"messed with." Again, nothing to lose so I unscrewed that screw
which released the larger circular part of the slug. This is the
widest part of the slug which has the grooves and is gripped to
rotate the slug in the wattmeter housing.
Once the finger piece was off, I could see a 1/2 watt resistor with a
piece of spaghetti over one lead. It was soldered on one side to a
small terminal which was one of the two connection pieces which are always
visible on the side. The other lead of the resistor connected
to another terminal and on to the top of a diode coming through the
remaining part of the slug.
Two more screws were also revealed and once they were removed, the
white nylon cover which shielded the primary RF detection pieces was
removable. This round white piece of nylon is the piece which you
see on the lower section of all Bird slugs. The slug I had was a 50C
which was calibrated for 50 watts in the range of 100-250 MHz.
The RF detection parts were a 1 1/2 turn coil of about #18 silver
plated wire connected to the diode on one end and a flat feed-thru
capacitor on the other. The white nylon cover was actually a
machined-out piece with room to go around the coil and feed-thru. I
had originally thought it to be just an inverted bowl-type cover but it is
much more rugged than that.
I did not bother the coil or other parts inside the slug once I
realized that my problem was an open resistor. This resistor was
marked 14K 1% and had, no doubt, gotten too hot from excessive power so it
opened up. As Fortune had smiled upon me, I had an exact replacement
resistor which helped to speed the repair. I carefully bent
the leads on the replacement resistor to look exactly like the one it was
replacing. The defective resistor was easily and quickly removed and
the replacement fit back perfectly. I tried to use the least amount
of heat on the connections so as not to risk changing the value of the
resistor.
Putting things back together, everything fit fine and there were no
left-over pieces (unlike some of my previous projects). The slug was
tried and worked as it was supposed to. At least, it read upscale
when power was applied through the wattmeter connectors.
Bird slugs are expensive because they are manufactured to close
tolerances and I imagine it takes quite a bit of time (Time = $$$$) to
assure the accuracy to which users have come to expect of Bird
products. My repaired slug certainly did read something but there
was no assurance that it would anywhere near the accuracy that was
demanded of that unit. I compared the repaired slug to another I had
which covered the same range and they read to same values. Yes,
since that one had been defective and I still needed that value, I had
purchased another. The repaired slug read the same as the
untouched, other one which had become its replacement. Lucky?
Probably. Happy? Absolutely!!
Had I been able to verify the contents and inner make-up of the Bird
slug earlier, that is, if I could have read what you just read, I would
have started the repairs much sooner. It may be that I was just
lucky and attempting this project again on a different dud slug would have
resulted in a much different outcome. I was, however, very pleased
with the final result on this particular attempt. If you attempt the
same, I hope you have similar success because, as we all know, "A Bird in
the hand is............ oh, never mind....."
----- K5LAD
Click
here to go to More Info on Bird Slugs
Click
here to go to Even More Info on Bird Slugs
Click
here to for Additional Info on Modifying Bird Slugs
Click
here to for Even More Info on Modifying Bird Slugs
Updated 11/13/06
11:36 AM
Note: Slug pictures
were borrowed from several peoples' ebay sale items.
Thanks!
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