I did the AM mod described on the Drake mod site some weeks ago with my T4X transmitter, the circuit is somewhat different than that described with the T4xB, but easy to complete, ran the pot out the side of the radio, should have run it out the back but no extra holes there on the T4X like there is on the T4XB...anyways...you have to be careful of a few things...keeping keyed down power no higher than about 20 - 24 watts seemed best..higher amounts started a pulsing effect on the output...less than that, around 10 watts, the output modulated with your voice, as is what it does when it was not modified. AM'ers say they dont like listening to the controlled carrier of the Drakes as the output varies alot with the modulation. With the mod, and putting out about 22 watts, the carrier and power level never drops...good clean sounding AM too. Now, as for the cooling, you WILL need to place a small fan out the back of the T4X and draw out the heat....on mine I used a 12VDC 4 inch fan and powered it with a 9 VDC wall wart...slower but completely quiet, running it with 12VDC was loud. Now, after transmitting I can put my hand on the top back corner of the Drake cabinet and its cooler than the rest of the transmitter...I feed my 22 watts to a linear (in my case its a Hunter 2000C) and get out a solid 350 - 400 watts AM carrier...seems to work very well for me...good luck...Tim K8WBL
From: [EMAIL PROTECTED] (Robert Schenck) To: [EMAIL PROTECTED] Subject: RE: [drakelist] T4X mod Date: Mon, 29 Dec 2003 06:48:19 -0500
For two cents, read on....
You have to seriously consider what you are getting for this mod and why you would do it. There is a reason for controlled carrier in the AM operation of the T4X. It has to do with plate dissipation in the 6JB6's. They are only rated for 17 Watts, and this mod can run you upwards of 25 W in each tube. The elevated temperatures will stress the seals on the leads leaving the envelope, not to mention the screen and plate, and result in shortened tube life in the process. We already have tube life issures and added muffin fans to try and extent life.... At the current prices and availability of 6JB6's, is it worth it? If you want to play with AM, and it sure is fun to do that, why not just run her through a linear? The linear will be loafing along with maybe 100 W of un-modulated carrier and give loads of headroom.
You can still run processed microphone audio directly into the 6AU6 modulator...or you can modify the internal microphone audio path for better low end audio. If interested, email me for details. HI FI audio does not just mean wider bandwidth audio, but better quality of your audio too. The idea is natural sounding audio....away from the compressed "monkey" sound of SSB.
>[EMAIL PROTECTED] wrote:
>Has anyone tried this mod and have any feedback as to performance on both AM
>and SSB?
>
>http://www.amwindow.org/tech/htm/t4.htm
>
>
>Alan KB7MBI in Woodinville, WA
>FISTS 5702 / ARS / Proud member of ARRL
>___ ___ . . . . . . ___ ___ DIT DIT
>
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