Whites 6000 serie 2 with 9.50 coil???

[Malospelos]

Good afternoon friends, I have a Whites 6000 series 2, I read a long time ago that these machines use 6DB coils and that they could be used with 950 coils of the next generation by changing a capacitor or adding, I don't remember well, I don't know which page it was on. read. and now I can't find it, does anyone know? Thanks for your help

[Carl-NC]

The 6000 coils had the TX tank cap inside the coil. The 950 does not, so you need to add a cap to make it resonate. The 950 should have an LTX of 540uH so adding a 1.08uF cap should get the TX running at 6.59kHz. No idea if the RX side will be correct.

[Malospelos]

Hello Carl, good afternoon, thank you for your response, I bought your book and I am learning things. I can use the coil, it is in resonance or at least it works, it discriminates, I can do GB, everything,... the only thing I notice is that the threshold is unstable and I have to constantly press the button to calm down. below. I thought I read that a capacitor was used to make the threshold more stable.Thanks

I forgot to say that I always use Gebmax and the threshold is more important

[Carl-NC]

The threshold is held by a retune circuit which can drift if the cap, opamp, or switch is leaky. This could happen with age.

[Malospelos]

Thanks, after all it is a 45 year old machine, all the capacitors still need to be changed to keep it updated, are some more critical than others? What would you recommend? Thanks for your time.

[dbanner]

the retune circuit in the 6000D series 2 is comprised of a CA3140 chip (U8], a 1K resistor (R45), a 1.0uF capacitor (C23), and a 1N4148 diode (D3). Also a 2N4302 FET transistor. (refer to the schematic diagram)

If the opamp (CA3140) or the capacitor (1.0uF) or the switch (2N4302) is leaky which happens with age, then one or all of these components needs to be replaced.

First start by replacing the capacitor with a new one. If the problem persists, then replace the transistor and finally the CA3140 opamp.

Excessive drift of the threshold which cannot be kept without constantly having to press the retune button is a common problem with these aging detectors.

[Malospelos]

Thank you very much, you have been a great help to me, you are great people. Now it's time to look for the parts that are not fake, I changed the capacitor and after a few minutes the threshold disappears and you have to press again, I think this is not normal, I suppose it should be a constant threshold. The same is normal on this machine, could someone tell me who has used it? Thanks friends.

[Altra]

It's very important to clean the circuit board around the 1uf cap, FET and CA3140. Over time the humidity and or salt air can cause oxidation around the solder joints. This leads to the hold capacitor losing it's charge much faster. Even if you don't find oxidation you should clean the board after changing any parts. Use any kind of alcohol and a tooth brush. Better yet is a small brass brush.

[Malospelos]

Good morning, thanks for your help.

I always use isopropyl alcohol to clean PCBs.
The detector was in very good condition, the only thing it had were the stuck buttons that I solved by adding a little fine sewing machine oil.

I don't think the fault is there? They work very well and everything runs smoothly.

I am currently using a 12" DD coil that was made for the white machines.

I get very good depth and it is good for mineral sites.

I will check everything again and as expected the transistor is discontinued and it is very difficult to find that is not fake, I have seen an equivalent that can still be found, it is a PN4302, could it work?

[dbanner]

I suppose any general purpose N-channel JFET should work fine. I always pay attention to the pinouts, I don't assume that all jfet in TO-92 package are standard pin config.
Age related leakage can be caused by several factors, primarily related to the degradation of the semiconductor material.

CA3140 may have degraded also, it's a Bi-MOS device.

No harm in changing it too with a new genuine part. Solder in a socket.

[dbanner]

PN4302 has different pinouts to 2N4302 it would seem.

Please check the respective datasheets to be sure, look at the order of pins 1-2-3 and source,drain,gate of both transistors to be sure.

Better to look for a general purpose jfet with same pinout configuration as original 2N4302. So you can solder it in just as the old one.

[dbanner]

The pinouts of these Jfets are tricky.

[Altra]

If all of the above fails. Check the two 470uf caps in the power supply circuit. C42 and C43 on my schematic. I think these form the analog ground? Any drift here or in the regulators could cause problems else where

[Malospelos]

Good morning, thank you again for all the contributions, I am learning a lot, infinitely grateful.

I will put a socket, I was able to get an original CA3140 in an old store, they did not have the transistor,

I will change the capacitors as you tell me, it is cheap and easy and can help improve the detector,

The equivalent appeared on Google, I didn't look at the pin distribution, I always consult with a device before soldering, I will ask the store what equivalents may be valid and I put it here in case it can be useful to someone else.

[dbanner]

The 2N4302 datasheet below specifies a low leakage device. However I don't quite know what leakage they are referring to.

"Off state" drain-to-source leakage? Maybe you change the CA3140 first (and also the caps in the power supply) and see what it does.

jfet-2n4302-2n4303-2n4304-interfet.pdf