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Rebuilding DX-40 - W4BTX
http://w4btx.com/retro.html
To avoid a heavy modulation transformer and extra tubes and circuitry, the DX-40 uses screen-grid modulation that, by its nature, restricts modulation to about 80%. This was good because it kept Novices from causing distortion.
Controlled carrier and audio mod for the Heathkit DX-40
http://amfone.net/Amforum/index.php?topic=30275.0
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
Heathkit DX-40 with Mic Gain, PTT, and other Mods - QRZ …
https://forums.qrz.com/index.php?threads/heathkit-dx-40-with-mic-gain-ptt-and-other-mods.760484/
The PTT saves wear on the selector switch, but is also makes the DX-40 super nice to operate on AM. Anyway, this particular DX-40 (I own 4, eh, eh) has two interesting mods seen here (not by me): First, if you are strictly an AM guy, the handy and smooth “guitar style” switch replaces a key. It makes tuning up possible without the key installed.
Heathkit DX-40 with Mic Gain, PTT, and other Mods | …
https://forums.qrz.com/index.php?threads/heathkit-dx-40-with-mic-gain-ptt-and-other-mods.760484/page-2
Heathkit and some others got into the "communications audio" school. Note that the DX-40 doesn't have any audio transformers; the entire screen modulator section is RC coupled. This makes for very wide audio bandwidth unless specifically designed to limit the audio response. 73 de Jim, N2EY
Heathkit DX-40 Restoration and Mods - Wireless Girl
http://wireless-girl.com/Projects/AMTransmitters/Heathkit-DX40/
Heathkit DX-40 Restoration and Mods. Note - This is a temporary page. I will get things organized soon.
Help with Heathkit DX-40 PTT - WorldwideDX Radio Forum
https://www.worldwidedx.com/threads/help-with-heathkit-dx-40-ptt.147995/
I recently purchased a heathkit dx-40 that works great. But some mods have been done. It transmits fine. Its supposecto have a ptt mod done, it has a four pin mic lug. Pin 1 is the audio and pin 4 is one of the two grounds from what I have found out. When I put it on "phone" and it is just keyed...
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