A quick question about grid dipper

[alvamabel2018]

Ok so I want to make another dipper, I have done a few now.
Cant get this one to work, instead of using an old airspaced or polyvaricon cap I wanted to use varicap diodes.
I built this circuit:
http://www.qsl.net/iz7ath/web/02_brew/15_lab/02_dipper/english/pag09_eng.htm
I realised that this had an error, the lower part of the tank isnt grounded, doing so made it work, then I found the same schem but corrected.
http://www.tradeofic.com/uploadfile/ic-circuit/20096263543515.gif
I can only get the circuit to work if I use a variable capacitor in place of the varicap diodes, if I put the varicaps in circuit the system wont tune it just runs at the lowest freq and if the tuning voltage gets to 0.6v and turns on the lower varicap it stops oscillating.
I'm using a J310 fet and bb510 varicaps.

 

[JimB]

Your second link does not work.
Do you mean this:
http://www.next.gr/circuits/VARICAP-TUNED-FET-DIP-METER-WITH-1-kHz-MODULATION-l53856.html

I can only get the circuit to work if I use a variable capacitor in place of the varicap diodes, if I put the varicaps in circuit the system wont tune it just runs at the lowest freq and if the tuning voltage gets to 0.6v and turns on the lower varicap it stops oscillating.

I think that the lower varicap diode is drawn the wrong way round.
Both diodes should have their cathodes connected to the junction of the 1k and 100k resistors.

JimB

 

[dr pepper]

Glad to see someone playing with a dipper, I have made a couple.
If your circuit works with a variable cap but not varicaps, its most likely an issue in the voltage control.
Firstly are you certain you havent got the diodes in backwards, what you say kinda points to that.
The you need to isolate the diodes from the osc dc wise with a blocking cap, then you need to isolate the diode with a high value resistor, 100k or higher, then the dc control wont damp the oscillation too much.
My latest dipper uses Led's as varicaps, and it has an Fm modulator to make it easy to find resonance, the original site has dissapeared unfortunately.