How to increase 2 XRF 286 to 250W CW

1. How to increase 2 XRF 286 to 250W CW Some modifications to the W6PQL kit By HB9BBD

2. Observations • The PQL layout may be ideal for some XRF286 but not for all due to variing internal match of the transistors • Unfortunately matched pairs cannot be figured out because of soldering/desoldering issues • The board did not fit to some used transistors I got so I had to fit the boards to the transistors • I built 10 double boards and try to summarize the findings

3. At a glance – some visible imbalances Thermal analysis of the original board at 94 W out Output capacitor is thermally the hottest part High power dissipation at 50 Ohm load!!! Mismatch at input and output is detected by different temperatures

4. Some just layed on flaps distribute the heat peak to the center of output hybrid Now at 10W in 180 W out in The hybrid is still lossy but now symmetrically loaded First try of improvement by mobile flaps out Less power loss at 50 Ohm load!!!

5. Parts to be replaced • Omit the tiny ceramic trimmer TC1 and TC2 and take a variable air capacitor (muRata)* or similar • Replace C2 and C12 by ATC 800A 22pF *Thanks to Mike, JH1KRC I have these on my bench..!

6. How to find out what to do? • As mentioned earlier, each transistor is unique in it‘s capacitance etc. This is why I recommend to find out on your board yourself, what is needed to improve. Do the following: • Prepare a teflon stick with little flap at it‘s end • At reduced drive (5W) carefully position the flap to the board ( without shortening DC !) • At position where positive effect is detected, lay down a flap and so on • Once no further improvement can be seen, solder all mobile flaps to the board • Beware of excessive RF exposure to your eyes, man!

7. These flaps helped to balance the amplifier in power and phase Input termination Output termination muRata 1-5pF

8. These flaps helped to balance the amplifier in power and phase • Output lines remarkably different.. • Due to high current, generously solder the cathode to the board! Thicknes improves here!

9. These flaps helped to balance the amplifier in power and phase • The hybrid also may need little mods (C2 still original size)

10. Final results • At input power of 14W the amplification is 14dB at 28VDC 16A • At 250W key down for 1 minute is possible with moderate heatsink without fan, max. pwr out 320W • Enjoy these amps and call me off the moon in CW ! • 73 HB9BBD Dominique JN47ee

11. Another Issue.. • The host of my EME site is a farmer. • Since farmers in HB9 get lots of subsidies, he wants a new barn for more cattle.. … and I want a better window to West!! … and a solid shack too!!

12. So the dish has to move • Since I did not want to disassemble and put together, the move was to be done in one piece • Total weight tower and dish is 5200 kg • Distance to relocate 28 m • All cabling off now..

13. The Hole • An engineer found out that the dish requires the Dishbase to be 1.5m above gnd for not touching the roof when turning.. • He further found out that this hole had to be made: New shack will be in here!

14. The Steel • 1400 kg was to be invested.. And welded too.

15. The Fit • Happily, the stainless steel base could be lasered along the plans, which had been designed in 1996 • So it needs to fit at first try.. 10xM33 in V4A quality

16. Steel into Hole • Next comes concrete.. But before, welding the grounding wire to the steel

17. The Concrete • 48 tons for the next 2000 generations!

18. The Move • If something may go wrong, it does!!

19. The Move

20. The End, and..(please, CW, USB or FM only!)