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The resistor can be of a value between between 22k and 47k Ohm.
The capacitor can be a simple disc ceramic with a value of about 0.001u F - often marked as 102.
These photographs show the 'Breadboard' method of construction using No.6 brass wood screws and screw-cups and a length of 1/2 inch thick by 4 inch wide planed softwood.
The wires and component leads are trapped underneath the brass screw-cups to make a connection at each junction point.
The OC71 transistor, on the right, is the first stage of audio amplification. I was introduced to the construction of TRF radios as a child with the Ladybird book 'Making A Transistor Radio' written by Rev. In a radio circuit the amount of this feedback has to be very carefully controlled and set to just the right level, just before it begins to howl. Starting with a crystal set and then progressing in stages up to a powerful 3 transistor TRF radio that uses a technique called , similar to the howl-around produced when putting a public address microphone too close to the loudspeaker.A popular design pre-dating the ZN' circuits was the H. I think that the AF125 or the older AF114 or AF115 or AF116 could be used too. The Ladybird book design uses the old Mullard OC71 and OC45 germanium PNP transistors which are unfortunately no longer made, but some supplies of these germanium transistors can still be found if you are willing to search.