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Am3 Radio Revision H

The object is to build a 3rd Generation simple radio illustrating the progress made over 60 years of hobby transistors. The design uses tuning, detection, and amplification. There is no regeneration and/or reflexing of the signals received.

Starting with the coil, the inductor value is 170uH. A second coil with identical properties is then made. The two coils are 54 turns of # 28 magnet wire wound on a 2 3/4" diameter plastic (hdpe or polypropylene) can with a length of 2.125". Both coils are made on separate cans. This allows three tuning configurations of parallel, series, and single. Bandspread can get large at 10pF per station.

Am3 Radio Rev. E

The tuning used is a straight-forward parallel resonance trap. For low cost and very good Q (550 at 1MHz) a ceramic-mica trimmer is employed. Arco type 463 will suffice. Surplus Sales of Nebraska has these with a 1/4" shaft. As built here (no shaft) a craft stick substitutes rather well. The fixed-value helper caps for the tuner MUST be of high Q and quality of construction. For the three padding caps, (39pF 82pF and 120pF) the 68pF input and ground caps, KEMET Goldmax 200V 5% are used. The combinations of the four padding caps allow 39, 82, 120, 159, and 202pF. At 1700kHz the 39pF cap is used with a small tuner capacitance (generally 15 - 20pF depending on actual build) with the coils paralleled. The ground cap (C5) and input cap (C3) are of the same value: generally 68pF is best suited for sensitivity/selectivity.

Power consumption is rated at about 0.3mW (300uW) with the emitter current at 100uA. The ground used here is the telephone ground just like the old rocket-radios of the 50's and 60's. Connection is to the green wire. Use station wire if possible (round cable as opposed to the flat cable).