For what value of L, will this circuit resonate at 332kHz?
Is there any specific formula to find out resonant frequencies of complex LC circuits like this one?
That isn't a resonant circuit so the answer can't be given.
The formula is 1/(2 * pi * SQRT(L * C); "one over two pi root LC- gives you the resonant frequency"
Your schematic shows no series or parallel LC combinations so there is no resonance.
Brian.
This is the original circuit...switches 2,3,5 of dip switch S2 are closed and switches 1,2,4,5 of dip switch S3 are closed
Looking at the coil at left...
The 15 pF capacitor is the main one figuring into the series capacitance. This value will be reduced slightly due to the other series capacitors.
To obtain 332 kHz resonance, the coil should be about 15 mH.
The formula is:
f = 1 / (2 x Pi x SQRT ( L x C) )
But there are two inductors...would both be of 15mH value?
I only tackled the one on the left because that looked like it would be easier to estimate (or guesstimate) a value.
The one on the right will be a lower henry value, because its influencing capacitors appear to be the 225 pF and 1000pF.
Notice the inductors are surrounding by dashed line figures.
I'm pretty sure these indicate metal shielding, and the arrows indicate a variable value. This is often done by turning a ferrite core which has screw threads. You would use a plastic tool (not metal which would throw off the henry value).
If you need exactly 332 kHz then you want two such coils. Adjusting one will affect the other. Furthermore you can't be certain the capacitors have the exact values that they are labeled as having. Hence the coils need to be capable of a sufficiently wide range of adjustment.
Yes you are right about the ferrite cores....is it possible that these inductors have lost their value over time as this is an old set and I cannot seem to tune it to 332kHz by turning the ferrite cores that is why I am trying to replace these variable inductors with two fixed ones so that I can tune it to 332Khz
It is far more likely for capacitors to change in value. Particularly old electrolytics.
You'll need to test each capacitor out of circuit to find out if they are still correct.
Also for switches to get tarnish on the contacts. Then they don't conduct. You ought to test for very low resistance through each set of contacts.
Do any of the switch settings work? So that you get operation? Or pick up some broadcasts?
Is there a reason you need exactly 332 kHz? Because the only reason I can think of is if this is an intermediate stage. In that case you only need to match two stages to the same frequency as each other. I'm pretty certain that is the purpose.
It is very unlikely your coils have gotten so far out of spec that you cannot adjust the left coil to some suitable frequency, and the right one to match.
Sorry I am not more experienced with radio reception so as to be of more help.