Gold Bug 3.5" Round Search Coil

[Steve Herschbach]

I have a 1990s era Fisher Gold Bug, the original 19 kHz analog version, long since replaced by newer models. The old 19 kHz model was not particularly hot, but it did have an ability to ground balance out some hot rocks that newer and hotter VLF machines struggle with.

Original Fisher Gold Bug Data & Reviews

The detector came with a 10" elliptical search coil. I have a couple very rare 3.5" round coils that Fisher made for these models before the little 4" x 6" elliptical replaced it. It's the smallest search coil I've ever owned for a commercially sold metal detector, making the unit into more of a probe than a normal detector.

The threshold was cutting out if the detector was bumped, something loose, so it's been sitting idle for a very long time. I decided it was doing no good as is, and by chance had an opportunity to call Felix at Fisher recently. Felix is another old-timer in the industry like myself, who I have not talked to since I left my old dealership in Alaska over eight years ago. Anyway, since the detector is still actually functional Felix figured they could give it a good refurbish and fix whatever is loose.

The main thing I wanted, however, was to get the detector tuned for the 3.5" coil. Most people do not know it, but analog Gold Bugs are hand tuned for every coil. The coil they ship with is tuned for the detector, or should I say the detector is tuned for the coil. Accessory coils may or may not be a perfect match if the original coil is swapped out for something else. Long story short is I am asking them to match the detector to the 3.5" coil as well as is possible.

The original Gold Bug is a genuine classic. Prior to it, detectors were large square boxes with extremely poor ergonomics. The Bug features a very compact control box that is removeable from a S rod, enabling easy chest or hip mounting. The design seems normal now, but you have to have used what came before to see the genius of what Fisher did with the Gold Bug. 19 kHz was also a radically high frequency at the time, as people were just catching on to the idea that higher frequencies are better for small gold nuggets than the lower frequencies that were the norm of the time. The 19 kHz Gold Bug replaced the 4.5 kHz VLF-660 Mother Lode as Fishers top nugget detector. Frankly, Fisher was not seriously in the game prior to this point, with Garrett probably the leader in VLF gold detectors at the time. A new company named Minelab was just starting to sell detectors in Australia, and had yet to really make a name for themselves.

Anyway, control box and coil boxed up and on the way to El Paso. I'll let you all know how long it takes and what the result is.

Here is a picture of one of the coils. The Gold Bug coils first used a gray dual lead cable, which was replaced very early on with the stouter black cable used to this day. This is the older coil of the two, though it also has less wear. The one I sent in has the heavier cable but is in poor condition. I need to reinforce the coil ears when I get it back since one is cracking. But I decided I wanted to use the coil with the heavier cable, with this older one serving as backup until I sort this all out. And in case anyone is wondering, the old 19 kHz coils do not work on the newer digital versions of the 19 kHz Gold Bug.

3.5" round search coil for original analog Gold Bug

To reiterate what a radical design advance the Gold Bug was at the time, here is a picture of the detector it replaced, the 4.5 kHz Mother Lode...

Fisher VLF-660 Mother Lode metal detector

And the new 19 kHz Gold Bug...

[Steve Herschbach]

The 19 kHz Gold Bug was kind of the SD2000 of the day. Prior to it, the best thing going was the 15 kHz Garrett Groundhog circuit. Magazines of the time had many stories of people in Australia cleaning up with these old Gold Bugs. That was, as you note, more a function of being first on the ground, not any magical powers the machine had. It is what I call a "low gain" 19 kHz, not as hot on tiny gold as the new 19 kHz digital models, which are running higher gain circuitry. As I noted, however, this allowed the machine to handle really bad ground relatively well for a VLF detector.

The coil does look tiny. Here is my father using one back around 1990. The coil is described variously as a 3.5" coil or 3-3/4" coil, but it is 3.5" without scuff cover, closer to 3-3/4" with cover. As you can see it is also very thin, especially compared to other coils of the day or even today. Most similar size coils are over twice as thick. Yes, this is a concentric coil, as are all analog Gold Bug coils.

The old coil I am having serviced was used without a scuff cover and is slightly worn through to the epoxy along one edge. The older coil has minimal use and still has the scuff cover on it.

Another note on old Gold Bug models. The earliest are like in the photos below, with a white lower rod as part of the two piece shaft. The coil cables are gray or silver, and did not go to black until later. A three piece rod was offered as an option, and it was so popular it eventually became standard.

FREE BOOK - Advanced Nugget Hunting with the Fisher Gold Bug

Bud Herschbach with original 19 kHz Fisher Gold Bug

Bud Herschbach with original 19 kHz Fisher Gold Bug

[GB_Amateur]

I assume Dave Johnson was still at Fisher (first time around) and had a major hand in the original Gold Bug's design.  How long after it came out before the Gold Bug 2 was released?

Is that gray cable on the coil in your photo actually shielded, double coax??  If so that sure seems weird.  And if not shielded, even weirder!

[RickUK]

Steve,i really do like reading these topics that you post,the images that you also add really complete the story so we can fully understand how these early classic detector and equipment was used.It all makes so much more sense when you can see the images as well.

Bravo,another classic article.

[Steve Herschbach]

22 hours ago, GB_Amateur said:

I assume Dave Johnson was still at Fisher (first time around) and had a major hand in the original Gold Bug's design.  How long after it came out before the Gold Bug 2 was released?

Is that gray cable on the coil in your photo actually shielded, double coax??  If so that sure seems weird.  And if not shielded, even weirder!

Dave started with Fisher in 1981 and the Gold Bug came out around 1990. Any detector is a group effort, but Dave is considered the key player on the Gold Bugs. The Gold Bug 2 came out in 1995, and Dave left at about the same time. See the forward in the book below for details.

FREE BOOK - Advanced Nugget Hunting with the Fisher Gold Bug by Pieter Heydelaar & Dave Johnson, Fisher Labs

[Steve Herschbach]

Some interesting early Fisher history from Dave Johnson including some details about the VLF-660 Mother Lode.

[GB_Amateur]

That's quite a recounting of history, through the eyes of an icon of metal detector engineering.  Ironically (maybe 'coincidentally' is the better word) I was thinking in literally the last couple days that it would be interesting to read about the milestones of metal detector development.  I think Dave nailed two of them -- ~1974 -- the invention of ground balancing VLF detectors, and ~1981 -- the development of motion all-metal and discrimination techniques.

There are other tidbits in that article, too, such as his statement "The lessons learned from the 1265-X made the later CZ's possible. The 1200 series is gone except for the 1280 Aquanaut which is a specialty nitch item: the CZ platform (originally the CZ-6) is still with us, circuitry almost unchanged 23 years later as the CZ-3d and the CZ-21."  (Steve, I think you've said this or similar here on at least one occasion.  Now we have it from "the horse's mouth.")

As I review my old treasure magazines from 1970 onward, it's an interesting contrast to today's development/innovation.  They went from no ground balancing, no discrimination detectors (BFO's and T/R's) to motion discrimination in about 8 years.  They didn't stop and rest on their laurels then, either.  And it wasn't just one company protecting (with armed guards) patents like they were Fort Knox gold.  It was many companies frantically creating products in competition -- great for the consumer. 

There has been speculation here that Minelab intentionally holds new detectors on the shelf until either competition starts to creap in or they need some extra capital.  Personally I question if they do that, but certainly back from the mid-70's all the way up into the 2000's I doubt anyone dare take such a risk.  "You snooze, you lose."

Thanks for the link, Steve.  (Got anymore?  😁)

[EL NINO77]

Steve .... Can you do a more detailed review of the Fisher Gold Bug detector with a 3.5 "concentric coil? ... and also a comparative comparison with some other gold detectors? ... on your more mineralized terrain?

I believe that this coil will bring increased sensitivity to very small gold ,,,

I think it would be an interesting topic ..

[Steve Herschbach]

Once I get the detector back I'll do something up. But I have used this detector and coil combo before and there are limits to what a small coil can do as far as enhancing small gold capability. The machine itself has inherent limits. However, nobody has compared the original Gold Bug to the modern digital version. Since I just happen to have a new 19 kHz model on hand, I will test them both on tiny nuggets to see just what the difference is. I believe it will be instructive as people tend to focus just on frequency, but there is more to it than that.

[Steve Herschbach]

On 9/23/2020 at 6:40 PM, GB_Amateur said:

Is that gray cable on the coil in your photo actually shielded, double coax??  If so that sure seems weird.  And if not shielded, even weirder!

The cable appears to be simple, cheap speaker wire. No markings on it. The connector is five pin but only four used. Two wires, clear and red, and the other two actually use the shielding from those two wires as connections.

Close up of coil cable

And the connections