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**diggerbarns** · 08-19-2007, 11:39 AM

BFO

Now thats a pity I just thrown away one of those, after no takers on Ebay. I never thought there were any parts in that plug. Are you sure about this.

**diggerbarns** · 08-19-2007, 11:44 AM

BFO

Thinking about it a bit, I do not think there would be any resistors in the plug, cant see the point. But I suppose there could be some small polystyrene caps just to trim the coils to the same freq. But I think it should work without these.

**kjamison** · 08-19-2007, 09:23 PM

Yep, it doesn't make sense but they do. I discovered this by taking one apart-it parts into three metal pieces. Inside one of these pieces is housed two capacitors and a resistor. When I bought Garett's whole kit and kaboodle, it came with two coil arrangements, one large coil and one small coil arrangement. Each arrangement consisted of two coils each. When using one of the (almost concentric) arangements you could switch from one coil to the other by means of a toggle switch on the rugged green housing into which the coil cables(military style) plugged into. I disassembled one of the connectors to discover two capacitors and a resistor inside. I have no earthly idea why they are there and not in the housing (or green box), but there they were... Something else came with the set---a metal wand and a green web strap so that you could form a switcheroo and have a hip or shoulder mount. The green wand was equipped with an extention cable which sported (guess what) a military style connector. Guess What! no cap's not R's inside!!! So, this connector will be part of the solution IF (that's a big if) I can find appropriate cap's and R's. My guess is these components form the initial stage of the oscillator for the coils suggested by generic BFO schematics. What the capacitance and resistance is inside connectors I don't know and neither does Garrett who doesn't have his schematics, but somebody out there knows, don't you think? These miniature things have a manufacturer, "Mial" and a hard to distinguish serial or catalog number. One R has faded bands not readable. Thanks for listening and .....help!

KJ

**kjamison** · 08-19-2007, 09:24 PM

Yep, it doesn't make sense but they do. I discovered this by taking one apart-it parts into three metal pieces. Inside one of these pieces is housed two capacitors and a resistor. When I bought Garett's whole kit and kaboodle, it came with two coil arrangements, one large coil and one small coil arrangement. Each arrangement consisted of two coils each. When using one of the (almost concentric) arangements you could switch from one coil to the other by means of a toggle switch on the rugged green housing into which the coil cables(military style) plugged into. I disassembled one of the connectors to discover two capacitors and a resistor inside. I have no earthly idea why they are there and not in the housing (or green box), but there they were... Something else came with the set---a metal wand and a green web strap so that you could form a switcheroo and have a hip or shoulder mount. The green wand was equipped with an extention cable which sported (guess what) a military style connector. Guess What! no cap's not R's inside!!! So, this connector will be part of the solution IF (that's a big if) I can find appropriate cap's and R's. My guess is these components form the initial stage of the oscillator for the coils suggested by generic BFO schematics. What the capacitance and resistance is inside connectors I don't know and neither does Garrett who doesn't have his schematics, but somebody out there knows, don't you think? These miniature things have a manufacturer, "Mial" and a hard to distinguish serial or catalog number. One R has faded bands not readable. Thanks for listening and .....help!

KJ

**diggerbarns** · 08-19-2007, 10:25 PM

bfo

I think that when they made these coils they put small poly caps in the plug housing so that all the coils were close in frequency. They would not need to do this with the extension lead. If you think about it, if you had a dual coil it would be a bit of a pain if you had to retune when you switched from one coil to the other. Better if both coils were close in frequency. So what is your problem. Is your detector silent or cant tune or what.

**kjamison** · 08-20-2007, 12:52 AM

BFO Inside Conector Compenents

Yep, exactly right; that's why some cap's and R's were outside the toggle! Where do you put them?...inside some spacious connector. Herin lies the problem: One of the connectors came up lame -- some sort of short, signals were intermittent: tilt one way great response. Tilt another none. So, flying by th4e seat of my pants I began to learn how to get into the connector, not knowing at the time that small compenents were wired therein. When the smoke cleared and I had pried my shoe out of my....anyway the connector was ruined and only one cap could be seen dangling by one lead, the other gone. No resistor in sight for the small search coil and an undecodable capacitor. Now that's my problem: what cap and what resistor do I need to rerconstruct a good duplicate connector so that proper signals are sent to the "box?" Where do I find them and how do I connect them?

**digger barns** · 08-20-2007, 10:23 AM

If Garrett made a lot of these coils they had to get them all the same. You do not have this problem. You just have to get this one working. So take all the components out of the plug and put it back together, then see if you can tune it in. You have to bear in mind that this detector was just a novelty and not much use for detecting. So how much time can you afford to spend on it.
I had one of these. I paid £150.00 for it about 25 years ago. That was a lot of dosh then. I had one big coil about 2 foot by 1 foot, was supposed to be great hoard hunter but it was not. I also built the one at www.easytreasure.co.uk that cost me about £3.00 and worked just as well. When I bought the Garrett I got fooled by a magazine article. I know better these days. Interesting to get you Garrett working though. Garrett must have made a lot of these because they even had their name printed on the Xtal.

**digger barns** · 08-20-2007, 10:27 AM

Arado VFA 90

I like to mess with BFO because coils are simple. Arado VFA 90 was the one. I wish I could get hold of one of those to mess with. Keep looking on EBAY but no luck so far

**digger barns** · 08-20-2007, 10:31 AM

resistors

The only reason I can see to put in resistors would be to lower the Q of the coil and make them a bit more stable. About 470 ohm or 560 ohm.

**kjamison** · 08-20-2007, 07:39 PM

BFO Attempt

Good advice--"clean it all out, hook it back up, try to tune." I did; it doesn't work. I know the box is ok because the other large coil (not ever very handy; seldom used) tunes in nicely. And the toggle switches back and forth. So, the problem isolates itself to the components inside the connector. Ah ha! back to square one ....needed to know: the capacitance and the resistance of the components.
I have a quote for you: A generic schematic posted on the internet is accompanied with this tidbit, "...the search oscillator. In this design, the frequency is approximately 370kHz. For years, this frequency has prevailed in metal detectors, because it yields the lowest sensitivity to ground conditions, such as moisture and density." Now what capcitance and resistance connected in parallel produces 370kHz?
I'll bet that'lll smoke smooth in sombody's pipe out there.

KJ

**digger barns** · 08-20-2007, 09:24 PM

bfo

forget the resistor this won't alter the freq. It is the coil and capacitors that set the freq. I do not think it will be as high as 370 khz. Over 150 khz is not legal, and Garrett will always be legal. more like 100 khz I would think. But the capacitor to tune the coil will be on the board close to the big tuning capacitor. I think your coil may be dud

**Carl-NC** · 08-27-2007, 03:14 AM

I opened up 3 Garrett BFO coil connectors this weekend. The first 2 had no components inside, and I was beginning to doubt KJ's claim. But the third does have components in the connector. I was not aware of this.

I have removed the rear half of the connector shell. However, I cannot get the cable/pin assembly out of the front half, so I can't tell what the components are. If someone knows how, I'll finish the job. But I really don't want to damage this, as it goes with my BFO Master Hunter.

- Carl

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