National Radio Institute (NRI) AM radio kit

Posted on Feb 7, 2014

This National Radio Institute radio kit covers the AM broadcast band from 550 to 1700 KHz. The set was designed to be constructed as part of a radio course taught through NRI. In contrast with some other correspondence course kits such as a later NRI chassis, it uses a safe transformer power supply. Tubes are a 6BA6 RF amp, 6BE6 converter, 6BA6 IF amp, 12AU7 detector and first audio, 6AQ5

National Radio Institute (NRI) AM radio kit
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audio out and 5Y3 rectifier. NRI was well-known as a correspondence school for electronic technician training. NRI also produced a line of kits such as test equipment and a simple Novice ham radio transmitter/ receiver under the NRI and Conar labels. I first thought the cabinet was an excellent home-brew job. After removing the chassis, I noticed a rubber stamp on the inside bottom of the cabinet. This was indeed an NRI-supplied cabinet which I am told was available at extra cost. The chassis has IF transformers of two different sizes, several large over-sized resistors, a 12AU7 (dual triode) in place of the usual 6AV6 for detector and audio preamp, a choke in the power supply as a partial PI filter, a negative power source for audio output tube bias, three 1000 ohm resistors in parallel to develop that bias, and some other unusual features. I was wondering if someone had substituted components or simply miswired a couple of items such as the power choke. It turns out that ALL of the unusual features were designed into the set. I obtained a paper copy from George K. of the 68 page NRI lesson set 7E1 for this radio titled "Practical Demonstrations of Radio-TV Fundamentals; Instructions for Experiments 61 to 70". The unusual parts were either recycled from previous experiments or were included for a series of tests conducted in the process of building the radio. The tests and experiments include a simulated series of induced...

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