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Title: Hi-Fi Audio and modulator mod for the Heathkit DX-60 / Dx-40 Post by: n1uvi on February 12, 2012, 12:54:20 PM I have performed this mod on a Dx-40 using a 6.3 volt filament transformer in reverse to supply the AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
negative 120 volts needed for biasing the modulator. Recently I applied this mod to a Heathkit DX-60 with excellent results. The circuit shown here, changes the 12AX7 speech preamp to resemble a Hi-Fi preamp. The frequency response is flat from 20Hz, out to 23KHz, with total harmonic distortion at 0.033 %. The changes to the modulator yield 100 % modulation and eliminate carrier shift. The resulting audio is warm and full, and very natural. Comments welcome. |