The collector of T4 feeds a tank circuit that consists of the winding 3-5 of L4, a fixed resonating capacitor and the Varicap diodes D3 to D6.
The biasing voltage applied to the Varicap through R25 determines the value of the Varicap capacitance and therefore the resonating frequency of the tuned circuit.
The secondary winding of L4 has one end at a fixed voltage determined by the voltage divider R17 and R18.
The other end (pin 1) feeds the base of T5 that is a common collector amplifier provided to drive possible external loads.
The same winding end going to the base of T5 also supplies a feedback to the capacitor voltage divider C17,C18, the center tap of which feeds the signal to the emitter of T4.