In figura 13, a este prezentat un aparat cu o schema simplificata, care nu necesita prea multe explicatii. In schema din figura 13, b, semnalul detectat ataca direct, fara condensator de cuplaj, baza tranzistorului T1. ceea ce face montajul mai sensibil. Reglajul amplificarii se efectueaza cu potentiometrul de 2 montat in emitorul tranzistorului T1 iar difuzorul in emitorul tranzistorului T2.
Bobina este montata fie pe o carcasa cu miez magnetic fie pc o bara d.e ferita lunga de 120 mm. In primul caz, se vor infasura intre santurile carcasei 56 de spire (circa 4 metri de lita de radiofrecventa), iar pentru uncie lungi se bobineaza 132 spire (cite 33 spire in fiecare compartiment) din sirma de 0,2…0,7 mm diametru, izolata cu bumbac sau cu matase. Nu se recomanda sirma izolata numai cu email, deoarece slabeste auditia.
Dezizolarea litei de inalta frecventa de email, pentru a fi usor lipita la terminale se face fie la flacara unei lampi cu spirt, fie cu ciocanul de lipit, pe o pastila, de aspirina, pina ce se curata emailul, dupa care se poate cositori capatul, pentru a prinde in manunchi toate firicelele de cupru.
In lipsa carcasei, bobina se poate infasura pe o iara de ferita, dupa ce i s-a aplicat un manson de carton, subtire lung de 5…6 cm. Pentru unde medii sunt necesare 90 de spire, cu priza la spira 10 de la masa. (2—3, fig. 13, b), iar pentru unde lungi —230 de spire cu priza la spira 20. Sirma va fi de acelasi fel cu cea specificata mai inainte.
Montajul de mai sus este foarte sensibilla auditia in casca si satisfacator in cazul montarii unui difuzor.
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