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Final iteration of my homebrew transmitter




 
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Author Topic: Final iteration of my homebrew transmitter  (Read 344 times)
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W8ACR
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« on: March 01, 2023, 08:31:21 PM »

Way back when, W3RSW dubbed her "Buzzard Baby", thank you Rick. Since that time, my homebrew transmitter has undergone multiple revisions using different tubes and circuit designs in the RF deck. It's been ten years, but I think I've finally hit the sweet spot. I have settled on a single 810 modulated by 811A's for 160, 75, and 40 meters. I can get 300 watts of carrier on all three bands running the tube conservatively at 1750 VDC and 250mA. On 20 meters, I use HK54's in a push pull swinging link design. I can get 225 watts of carrier with 1750 VDC and 200mA. The last bit of tweaking will be to get the HK54's to work on 15 and 10 meters now that the sun is cooperating again. I need to find grid and plate tank plug in coils for those bands, but I can wind my own if need be. Here are some pics of the 160/75/40 RF deck. I'll post some pics of the PP HK54's later.

Comments:
1. This transmitter works FB, but will not win any beauty contests. Cosmetics was never a strong suit of mine. Maybe I have one more transmitter build left in me. If I find the time and energy to build another one, I'll try to make it look good too.
2. The design for the 160/75/40 RF deck uses a pi network plate tank and grid neutralization of the 810 triode.
3. The padding capacitors for 160 and 75 meters simply clip onto the tank circuit leads. This eliminated the need for heavy duty switching. Not pretty, but easy and functional.
4. The grid tuning capacitor is underneath the chassis
5. The plate choke is handwound homebrew. I believe it is #26ga enameled soft copper. I think it is about 350uH.


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