Tracker IV Tx circuit

[dbanner]

Well, this is what I've drawn. I'll update and complete the component values, thanks to all.

I can't see how that circuit is supposed to oscillate, unless there are caps in the search coil assembly, even so, how do you get to a colpitts from what is on the PCB? Components are missing no doubt, but where.

[dbanner]

Better for everyone to look same direction. More readable.

[dbanner]

can't see how that circuit is supposed to oscillate, unless......

Now that the scheme is re-arranged, I can see a clever oscillator trick, I think, using the nand gate along with a 4016 switch. I'm not sure.

There still need to be a parallel Cx in the coil assembly for the Tx coil. I don't recall seeing a scheme quite like this one.

[dbanner]

The thru-hole and SMT schematics are absolutely identical. The one shown has SMT 1% resistor values.



Definitely.



Looks like it. Corrected/missing values are:

C4,C13	10n
C2,C27	120p
C3,C5,C6,C8,C12	220n
C7,C9	3.9n
C11,C16,C22	22n
C14	470n
C17	6.8n
C20,C21,C23,C19,C26	100n
C24	1u

Also, U3-pin6 connects to U3-pin2, not pin1.



The Tracker 2 is identical to the Tracker 4 except that the speaker driver has a 2-transistor gain stage which might give it the perception of more sensitivity.

The power supply in this circuit is most confusing to follow and trace out. Very strange. 2 x 9 volt batteries, but only one npn transistor and zener to regulate the positive rail. Beyond that it gets tedious.

I did my best with the drawing so far. Updated all the values.

[dbanner]

latest V1.0

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latest V1.1


these are the results

[Skippy]

"There still need to be a parallel Cx in the coil assembly for the Tx coil"

I assume it's going to be the same as many other BH machines. The TX is tuned to 6.6 kHz, internal C is usually 220nF + 22nF , in parallel with 2.4 mH coil inductance. ( I hope I remembered that correctly )
The gain stage that completes the feedback loop comprises the comparator fed from the coil via cap C23, squared up by a Schmitt gate, switching the transistor base on/off. The transistor is driven as a current sink, rather than hard on/off.

The RX coil is not tuned by any internal coil cap.

I wonder how much trouble it would be to hack this circuit to give tone-break audio. It's one of those features that some folks like about that Gold Century machine, the GC1023 ? Simple and cheap, but with a feature typically only found on higher-end detectors.

[dbanner]

"There still need to be a parallel Cx in the coil assembly for the Tx coil"

I assume it's going to be the same as many other BH machines. The TX is tuned to 6.6 kHz, internal C is usually 220nF + 22nF , in parallel with 2.4 mH coil inductance. ( I hope I remembered that correctly )
The gain stage that completes the feedback loop comprises the comparator fed from the coil via cap C23, squared up by a Schmitt gate, switching the transistor base on/off. The transistor is driven as a current sink, rather than hard on/off.

The RX coil is not tuned by any internal coil cap.

I wonder how much trouble it would be to hack this circuit to give tone-break audio. It's one of those features that some folks like about that Gold Century machine, the GC1023 ? Simple and cheap, but with a feature typically only found on higher-end detectors.

I don't like the whole Tx circuit. What is the advantage in her? Save one transistor in favour of making use of extra left over schmitt gate and one leftover switch? Then again, I notice only one opamp left over in whole circuit. Very frugal design.

[Altra]

The speaker should probably go to B+ and not the virtual ground? When I get time, I will try to trace that part. Or maybe Carl can post that part of the schematic

Dbanner, I think the unused op-amp may drive the analog meter on J2 and J5?

[dbanner]

The speaker should probably go to B+ and not the virtual ground? When I get time, I will try to trace that part. Or maybe Carl can post that part of the schematic

Dbanner, I think the unused op-amp may drive the analog meter on J2 and J5?

There doesn't seem to be a connection to pin 1 on U4 (LM324) on the PCB so this amp is not used. You can verify this on your board.


Tx mod.zip

I use this circuit instead.

[dbanner]

I have not looked at the audio output stage closely. But it doesn't look right. As for the meter, I think it is useless.

[dbanner]

I use this circuit for power supply. Single battery ideal.

Can you check the zener value on your board? I would like to get my head around the original power supply.

[dbanner]

There is also this scheme.

bh4_sch.pdf

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I suspect that the original power supply may not be symmetrical. Who knows?

[Altra]

The zener with a series 1K equals 10.9v. I'm guessing the series batteries (18v), not utilizing the center tap between them. The circuit runs on 10.9v, virtual ground is 5.4v and audio output connects to 18v?

Add: I found the old coil. As Skippy said there is 220n cap in parallel with the Tx. The tx coil measured 2.58mh 8 ohm

Add: The audio transistor Q3 smd "2U" is a MMBTA63 which is a pnp darlington. One side of the speaker is connected to B-