I have found theese oscillators:
https://www.next.gr/circuits/oscillator/low-frequency-oscillator-c38534
https://www.next.gr/circuits/oscillator/sine-wave-oscillator-low-frequency-constant-amplitude-c40904
But...
-How many Ohms should the potentiometer RV1 have?
-What zener voltage should the zener diode ZD1 have?
--Can i change the resistor RL to a potentiometer to make the ampltude adjustible?

I need a signal 0 - 1600Hz, maybe 1800Hz.

Thanks!

 

From the website:
R6 and ZD1 provide a form of amplitude limiting by preventing excessive signal swing and reducing clipping after the oscillation has stabilized.

I would start with a zener a little less than half the supply voltage. Powered from a 9V battery, I would select a 4.3 volt zener.

 

the second circuit shows Rtotal=1k and the wiper near max. (0.9xx)
yes you can change RL to potentiometer to select amplitude

 

BOTH of the variable resistor values are given The setting is done to provide the desired operation, so YOU have to adjust them. But if the associated text does not mention the zener voltage at all, then you may need to experiment.
A fair guess is about half the supply voltage. You could experiment with a string of forward biased silicon small signal diodes, (1N914, or even 1N4001 series power diodes. Whatever is cheap or on hand.

 

What was not mentioned were how muchdistortion is allowed and the desired frequency stability, and the consistency between units, if they are for production. The two transistor oscillator appears to have 2 resistors and two capacitors affecting the frequency and distortion, while the single transistor oscillator has three of each that affect the frequency but only one resistor affecting any distortion.