RELIC HAWK

[porkluvr]

Small yellow ceramic with 105 label.

Owww.

You should use a high quality 1uF cap. Two high quality .5u in parallel is just as good (if they fit) but please do not use ceramic cap!
Polyester (mylar) will probably work but you really REALLY should use polypropylene for the tx tank. PP is low loss and temperature stable. Mylar is inexpensive, and I don't know that Minelab doesn't use that here - but I wouldn't. PP are kind of big so use 50V to 100V unit. Stay away from more common 250V or 400V because they get really big.

If you come across Polycarbonate, they're maybe second best - but don't waste time trying to find them because they're mostly (or maybe completely) discontinued.

You will almost certainly need an oscilloscope. I know it's been done before, but I think that it's crazy to expect to have a successful project without one. You'd have to be very lucky or else very smart and experienced.

I think Fred was trying to suggest that my idea about frequency jitter was far fetched. I hope so!

[robopatt]

I agree with you Porkluvr.
You have a point.
I will buy one scope ASAP.

But have try your advice.Have used 1m 100V Polycarbonate Capacitor.
Now frequency is 4,66kHz.
Disc mode little bit stable.But still this poor sens.
I will try 700 as you sad before.

Forget to mention that I have changed D2 joint between 27k and Q1.
Q3 base changed between 10K and 27K.
Have took this 100k between Q2 and Q3 and solder under PCB on Q2 base and Q3 collector.
I am almost 100% shore they should be this way.

But you will tell when check with LT.

And because no one with scope have done this its a small but progress

[Fred]

I think Fred was trying to suggest that my idea about frequency jitter was far fetched. I hope so!

No, it was just a cheap joke...sorry

[robopatt]

Porkluvr,
Now I have used plastic 1m .
Use DL6243 shows 1m.
Frequency is now 4,85.And performance is just good now.
I attach 150ohm speaker.Good
Now I have to match my RX resistance and inductance because they are low.
You were right when you say that we will face problem whit power.Its eating the battery in no time.

[porkluvr]

No, it was just a cheap joke...sorry

I can make some BS sometimes, without meaning to. You don't have to be sorry. I can take a joke. grrrrrr [just kidding] grrrrr
You cannot make an omelette without breaking some eggs. (That's a CHEEP joke.)

I will try 700 as you sad before.

You misunderstand my meaning. I was suggesting that your capacitor may be 700nF which is bad. I was not trying to suggest that you should use a bad part. 700nF would account for the oscillator being off frequency by almost 20%.
ummh, Have you measured the value of the capacitor that you had at first? Why not?
**********************
Funny thing about this oscillator is that at 5kc it's a power sucking pig, but after bumping up to 20kc, appears to be very reasonable. I fiddled with the parts and through trial and error found a combination that gives high output and low distortion, with low(ish) power consumption. Hmmm. Good thing I never finished that other thing I was working on. This should be included.

If LTspice can be believed this absolutely blows the Tesoro Lobo oscillator out of the water AND it requires NO adjustment. Installing a TL061 opamp reduces supply current to about +/- 3.5mA. It's a bit higher with an 071 (or 081).
I will get some data together and probably make an informational post over in the "Lobo Improved" forum within a day or two.

[robopatt]

You are right Porkluvr.The old one shows 700n!!Maybe I overheated or some short.
Now its working good.
Almost.
The shuting between targets is not good enough.Too slow.

[porkluvr]

Too slow?

If I understand your problem correctly the RC network at the comparator input may be the problem. You could try reducing either component by a factor of 2, 5, 10, who knows. Lets say 5. Change either R to 100k or change C to 20n.

Here's something better: the diode should be connected to the RC junction instead of the comparator output?

[robopatt]

Yes,
You get it right.
But you are using realy wrong schematic.
You should use last posted here.
And on this its R68 470K if I understood you right.But I cant see this capacitator.
Now its more stable.
Still a lot of work before field test.

[robopatt]

Porkluvr.
You should look this one.
As you can see there are diferances.

[porkluvr]

space heater

Here's something I don't understand. It looks like all that U5B does is output -2.5V and then draw 25mA through R28.

WHY?? What possible useful function does this perform?

Ummh, besides being a 62.5mW space heater?

Maybe it is supposed to stabilize ground. If so then it seems to me like an inefficient way to do so. You won't find me copying that scheme. It's wierd. WIERD. (Arrgh.)

[ivconic]

Ask Max, it is redrawn from schematic he posted a while ago.

[porkluvr]

Ivconic,
I'm not meaning to throw stones at you, Max, or anybody, and I don't want to wear on your patience. It takes a lot of time and effort to RE one of these things and I'm grateful to all who do so. I'm not intending to belittle anybody's effort.

If it's a mistake, then it probably won't hurt to remove the resistor and possibly save some battery juice. If it's for real, then maybe somebody will divulge its purpose.

I saw it and wanted to point it out for what it's worth, because it's confusing (to me) and MAY be a mistake, but I don't know. I'm not well educated and there are all kinds of tricks that I would never think of that some folks have up their sleeve!

[robopatt]

Interesting is that U7 is 393.And on previous schematic its TS27M2.
Why?Its it mistake or some mod?
I have noticed that 339 is missing.And this IC is part of the sound section.But maybe its vital to use this one there.

Porkluvr,
Do you think that if we remove this R28/100R/ the problem will be solved?
I will try remove this but its elsewhere.
Its there on max schematic,but there is used with 074 for s/m/l.And now only S with 071.But its still compensating something.

[Unregistered]

Interesting is that U7 is 393.And on previous schematic its TS27M2.

A simple test could be to install TL27M2 or TLC27M7 and see what happens. If you don't have those, TLC2262 should work.

If you don't have either of those, maybe a LM358 or LF442 would work but they could NOT be considered best choice replacements. If your detector works good, great. If it doesn't work so good, you should obtain one of the first three amps listed or do some research for a good substitute from another manufacturer.

Install a socket if you think you might need to experiment with U7.

You could possibly remove R28 and save battery power, but only MAX or somebody with RH could know it there is an error. Do you see 2.5V at the top of R28?

One problem at a time.

[robopatt]

Do you see 2.5V at the top of R28?
Nope 4,95!

I have try TLC272 and LF442 on this 393 place and they only made the sound worst.