Cobra search coil

[mikebg]

The discussion is interesting and going in the very good direction. Set up however from the detector CobraKing. I send the part "of the true" schema KingCobra.
The oscillator is very strange. The input amplifier is also atypical. The all this detector is atypical, but works sensationally.
Mrand

Thanks Mrand for the posted part of true circuit diagram. It seems absolutely different and i like it.
I finded in WEB the following circuit diagram:

[Mrand]

Sorry, I think about Cobra II production Discovery Electr. This is much more interested Cobra Gold Moutain Cobra (from your schematic) is typical, some modified Tesoro. This not especially interest for me. Detector from my schematic was know so Viper.
Mrand

[WM6]

Some more clarification about "Cobra's":

http://www.findmall.com/read.php?56,1150493

Read JB(MS) comments.

Interesting (citation): "The current Cobra and Viper models they sell are made in China and aren't close to the Discovery built detectors in performance."

[mikebg]

Sorry, I think about Cobra II production Discovery Electr. This is much more interested Cobra Gold Moutain Cobra (from your schematic) is typical, some modified Tesoro. This not especially interest for me. Detector from my schematic was know so Viper.
Mrand

Mrand, can you post the other part of schematic?

[Altra]

Mike,

You can see a picture of the CobraII pcb here.
http://www.geotech1.com/forums/showt...ighlight=cobra

I have a circuit board if any body is interested. It was a nice
detector designed by George Payne. The main problem was the
cast aluminum box made it very heavy.

Regards
Mark

[mikebg]

According to web information, Cobra, Viper and Discovery are not names of different metal detectors, but different companies producing metal detectors.

[mikebg]

According to web information, the companies White's and Discovery are neighbors.

White's Electronics, Inc.
Physical Address: 1011 Pleasant Valley Rd., Sweet Home, OR 97386
Mailing Address: 1011 Pleasant Valley Rd, Sweet Home, OR 97386

Discovery Electronics, Inc.
Physical Address: 1415 Poplar St., Sweet Home, OR 97386
Mailing Address: PO Box 502, Lebanon, OR 97355

[mikebg]

According to web information, the companies White's and Discovery are not only neighbors. They use the same preparations to produce "TWO BOX" machines.

[Altra]

The original post was for the "Cobra", it was a
Tesoro Clone, made by "Gold Mountain",sold by Kellyco.

The CobraII was made by Discovery Electronics and was
sold by Kellyco. Discovery sold the same detector as
the "Tresure Baron" which had more feature.

From what I understand, Discovery Electronics was founded by
ex employee/engineers from Whites Electronics. Which had a working
relationship for a number of years. Later they went their own way.
Thats why they are located in close proximity and their products look the same.

Viper Detectors are chineese crap, that Kellyco sells

Viper and Cobra are Kellyco Brand names not manufactures.

[mikebg]

The illustration attached at posting #21 was not extracted from kellycodetectors, but from site
http://www.metaldetectorsbybrand.com/

According this site, the brands are:
White's, Garrett, Minelab, Fisher, Bounty Hunter, Teknetics, Predator, Titan, MP Digital, Cobra, Viper, Nautilus, OKM, Lorenz, GPL, Pulse Star, JW Fishers, EXcelerator and Anderson Rods.
I know that "Pulse Star" also is not a company name. The name of producer is TB (Thomas Breuer) and his site is
http://www.tb-electronic.de/

I'm looking forward mr Mrand or anyone else to send in the forum the rest of the circuit diagram in posting # 15 to understand how it works. It differs significantly from a conventional metal detector. See how by means of L1, inductively is loaded the RX coil L3 with resistance of R1:

[Mrand]

Sorry for the delay. At present I am very busy. (With what? Soon I will show). Circuit of the detector is very interesting and atypical through. It works superbly. Worth it is the wider discussion on the forum. Therefore I send the full schema. I drew him directly from plate. 2 weeks of the difficult work, because somebody applied crazyautorouter . I hope that I did not commit errors.
Mrand

[mikebg]

Thanks Mrand.
For what model we should search WEB for instruction manual? Cobra II?

[mikebg]

Errata in drawing

Errata in Cobra 2 drawing.

I have not managed to find instructions for use of the Cobra 2, to convince that what I say is correct, but based on the lettering on the circuit of Mrand in postings # 26, I think he has made the following errata:
1). Supply rails are +4 V and -4V relative to ground if battery voltage is 9V (as is written near to it).
2). Resistor R107 should be connected to inverting input (pin 2) as shown below.
3). Capacitance 620p of C107 is too large. If it is 10 times smaller, it will form cutoff frequency 26kHz which is more acceptable than 2,6 kHz.
Please somebody to help me to find instruction manual for this mashine!

[Mrand]

I have manual in the PDF format for Cobra. Now I can't find him. Probably "the devil covered him with the tail". When I will find, at once I will send.
I once again will check, but rather I didn't commit the error. This detector is the collection of unconventional solutions. The supply voltage is not +4V, -4V. I accepted the unlucky convention (I drew for myself). It should be: 0V (not -8V) and +8V. The masse is 1/2 Uz (+4V). The detector is supplied from 8 AA (alkaline battery or Cd-Ni akku).
Mrand

[mikebg]

Hi Mrand,
Explain me, please, voltage across TX coil. What means notation " 7.8Vp":
a) Amplitude (peak) as shown with Vp in the figure below,
b) Swing (peak-to-peak) as shown with Vp-p below, or
c) Vrms measured with an AC voltmeter.
How is DC voltage supplying the oscillator (Q101)?