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Controlled carrier and audio mod for the Heathkit DX-40

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Author Topic: Controlled carrier and audio mod for the Heathkit DX-40  (Read 7072 times)
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Posts: 47

« on: January 26, 2012, 02:54:35 PM »

I recently began restoring a Heathkit DX-40 and put it back on the air, a very fun project indeed.
Details are available on my QRZ page, please feel free to check it out. Anyhow, not finding any
reference to any DX-40 mods, after trying several of the DX-60 mods on the DX-40 and not having any joy
I managed to come up with a mod that works quite well on the DX-40. Much like the DX-60 mods that
are out there, however this mod uses a 6DR7 tube in place of the 6DE7 modulator.
The 6DR7 is a dissimilar double triode like the 6DE7, the second triode is identical but the first triode has a much higher
amplification factor than the 6DE7.
This mod  provides 100% modulation with very good audio frequency response.
The resting carrier is 12 to 15 watts, and carrier shift is eliminated.
The negative 120 volt DC supply is obtained by using a 6.3 volt power transformer in reverse,
that is as a step-up transformer, using the filament voltage available in the DX-40

* dx40mod.jpg (73.43 KB, 688x415 - viewed 2448 times.)

* 120vpower.jpg (26.45 KB, 487x176 - viewed 1463 times.)
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