I2MZC ha scritto:Ma ho un dubbio sulla polarità della batteria dei filamenti, infatti così com'è il potenziometro regola un tensione positiva sulla griglia della prima valvola.
Carlo I2MZC
Carlo, lo pensavo anch'io. Ma una ricerca su riviste d'epoca mi ha confermato che il collegamento è giusto. Ti riporto ad esempio lo schema del ricevitore Lewcos Ultra Short Wave Receiver (da una brochure del 1930).
Dalla rivista "Wireless Constructor" di luglio 1927:
"Practical experience shows that few 4-volt and 6-volt valves are at their best as rectifiers when the grid return is made directly to L.T. positive as shown in the circuit diagram. Usually there is a distinct improvement in signal strength if the grid potential is made rather less positive, and this is clearly all to the good from the point of view of selectivity, since the smaller the flow of grid current the less will be the damping introduced. Fig.2 shows how an improvement can be effected by the use of a potentiometer wired across the L.T. leads. ...The writer finds that with most valves the best general working conditions are obtained when the slider of the potentiometer is almost in the middle of its travel, slightly nearer the positive end than the negative."
Tonino
# ARO 440/0 
Edoardo IK0QDQ
