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Hi-Fi Audio and modulator mod for the Heathkit DX-60 / Dx-40

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Author Topic: Hi-Fi Audio and modulator mod for the Heathkit DX-60 / Dx-40  (Read 8744 times)
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« 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
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.

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