Step 1: Circuit
Antenna catches fm waves, first transistor works as oscillator. R1, L1 and C1 determinates oscillation frequency. Internal freq and cathed freq overlaps and gets more power. Germanium diode detects audio freq. T2 and T3 works as audio ampflifier. Last condansator connected to jack is 45uf electrolytic con.
Note: if Fm broadcasts are weak or far away in your area, please use v2 circuit in troubleshooting step! Thank you.
Step 2: Work
Parts values in circuit is critical for oscillation and biasing of transistors.
You may use any kind of earphones. No high empedance earphones or crystal earphones needed.
C1 is 80-140 pf variable condensator. Once tunning with C1, you can fine tune with P1. Other potentiometer P2 is for volume control.
Step 3: Troubleshooting
2- There is a "hush" but no radio signals: check your battery it must be about 6-9v. If everything ok but still no signal, genly compress coil from laterals or get wider by your two hands.
3- Radio signal is not stable: in best receiving, hot glue your coil to fix in stable condition
Also if there is too many elegtromagnetical pollution in your area, it may be necessary to faraday isolation for your tuner part. To obtain this, aliminium foil coated cardboard may be good idea. Or you may try 2st version of circuit above. If u realise this 2nd version take p1 and c1 to middle position, move p1 till hear fm hush then search channels with c1.
Step 4: Putting in a Case
Tips: if u wanna make soldered version make circuit on a wide area. Also coil lenght is very important to obtain fm bandwidh.
Step 5: Whats Next?
Will be here shortly.