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Title: National NC-300 filter choke Post by: k7mdo on January 01, 2020, 05:48:56 PM Well one of my NC-300's just went quiet so after trying the usual stuff I took it out of the cabinet.... turns out there is an "open" filter choke that doesn't even show on the circuit diagram. It is between the two filter capacitors as a "smoothing" choke.... but interestingly the published circuit diagram shows a 33 ohm 10 watt resistor... no choke shown.
I think they improved the radio at some time and I don't have a current diagram but was wondering if the choke might be available or can I simply put in the called for resistor. I am leaning away from the resistor idea as National must have had a good reason for the improvement? The part number is Thordason A-12167 and I don't see it in the catalog I have. Anyone else run into this and any other ideas... I am willing to buy a choke but was surprised at not finding it on the circuit diagram. 73, Tom Title: Re: National NC-300 filter choke Post by: k7mdo on January 01, 2020, 11:01:22 PM After some internet searching i think they added this choke in place of a 330 ohm 10 watt resistor some time during later production. Never made it into the schematic. AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
I've got some old choked and one looks close... 10 Henry 290 ohms.... Tom |