Help. FISHER GOLDBUG g2

[Carl-NC]

It would require a major redesign of a lot of circuitry, so not really.

[Arcoman]

It would require a major redesign of a lot of circuitry, so not really.

Reduced resistor R1 TO 1.2 kom. The current increases by only 4 mA. capacitor c57 decreases, the current does not increase. What else to try. At least tell me the direction. Add 10-15 ma.

[Arcoman]

In this device, are both TX circuits tuned to resonance or not?

[Carl-NC]

The TX circuit uses a resonant boost circuit, don't mess with those components. You can decrease R1, increase R2, or decrease R3. However, you will probably need to add a series diode to Q1-collector to prevent it from saturating. An increase in the TX voltage swing can also mess up the phase comparators (U1,U2) which might need recalibrating.

[Skippy]

Quote:"The TX circuit uses a resonant boost circuit, don't mess with those components"
Pretty good advice, mainly because few people have any understanding of how it functions ... what determines the tuning, what the second inductor does , how the transistor 'switch' operates.
However this post contains an explanation, if you think understanding it would help:
See posts #126 to #133
https://www.geotech1.com/forums/foru...443#post313443
And for interest, another ( rough ) interpretation of the TX850 schematic:
https://www.geotech1.com/forums/foru...941#post312941

[pito]

Reduced resistor R1 TO 1.2 kom. The current increases by only 4 mA. capacitor c57 decreases, the current does not increase. What else to try. At least tell me the direction. Add 10-15 ma.

where is schematic ?

[Carl-NC]

where is schematic ?

See post #7.

[Arcoman]

I succeeded. I thank those helped and those who did not help. But especially those who helped))). + r63 booster resistor 10kom

[Arcoman]

The TX circuit uses a resonant boost circuit, don't mess with those components. You can decrease R1, increase R2, or decrease R3. However, you will probably need to add a series diode to Q1-collector to prevent it from saturating. An increase in the TX voltage swing can also mess up the phase comparators (U1,U2) which might need recalibrating.

nothing ventured, nothing gained, fortune favors the bold, no pain, no gain

[Arcoman]

I have a dump po. You can link it here.?

[pito]

I succeeded.

Are you sure ? What is the difference of voltage on Tx coil ? Keep in mind, doubling the voltage will increase detection range only 10% to 20%, to double the range you need increase amplitude 10x times, to do that use TC4420. Be careful, the voltage will rise above 100V, during testing disconnect R70.

[pito]

Probnik 3,
should be 19.2kHz not 38.4, increase C1 = tune for resonance.

[Skippy]

Doubling the voltage will give about 14% air-test gain in 'depth', and in the ground, somewhere between 0% and 14% gain ---- expect much closer to 0% than 14%.
I personally would suggest splitting the 'doubling' between the TX and the RX; for example have 30 - 40% more TX current, and have a gain increase of 30-40% in the RX stage, such as the first pre-amp. You may find such increases in overall gain give better results when using the small 5 inch ( 125mm ) search coil. And if you use a large coil, they are probably useless, and may be annoying.

Nothing ventured, nothing gained; fortune favors the bold; no pain, no gain; pain is temporary, glory is forever; chicks dig scars.

[pito]

pain is temporary, glory is forever; chicks dig scars.[/B]

current is not the best parameter for testing Tx coils, the best is place the Rx coil at a distance of about half a meter from the Tx and observe its amplitude.

[Arcoman]

Doubling the voltage will give about 14% air-test gain in 'depth', and in the ground, somewhere between 0% and 14% gain ---- expect much closer to 0% than 14%.
I personally would suggest splitting the 'doubling' between the TX and the RX; for example have 30 - 40% more TX current, and have a gain increase of 30-40% in the RX stage, such as the first pre-amp. You may find such increases in overall gain give better results when using the small 5 inch ( 125mm ) search coil. And if you use a large coil, they are probably useless, and may be annoying.

Nothing ventured, nothing gained; fortune favors the bold; no pain, no gain; pain is temporary, glory is forever; chicks dig scars.

1. the depth will not double. 2. the resonance will go away. 3. The frequency response will be bad.
4. why disable r70?
5. How to increase the gain? change what? your suggestion
6. regarding air power. it was 25 for the average maneta. became 32-33. in discrimination mode.
7. How to place the tx coil 50 cm from the rx. cut the sensor? )
I achieved maximum sensitivity without loss of stability. The device is sensitive and quiet.