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I plan to incorporate a 150 watt boost converter into the amplifier to provide 28V (with additional filtering, if needed), so that I can get the full 40 watts output. I mainly want to use the amp for SSB anyway, since CW (which I never use anyway) and digital generally work reasonably well on QRP anyway. And yes, I plan to use the extra resistor so that it reduces 5watts input to 1 watt, as I want to use it wit not just my Bitx40 (which I have not completed yet), but also my Xiegu X1M Platinum which seems to operate at a fixed 5 watts output. No such problem using it with my mcHF, as I can set the power for anywhere from a half watt up to a max of 8-10 watts (depending on the band), but it will be nice to set it for 5 watts and run it into the amp for sideband use. One of our club members gave me the original QST magazines with the build article (part 1 and 2), so I am set there. Rich KC8MWG On Saturday, July 1, 2017, 11:17:03 AM EDT, <phil.erickson@...> wrote: Hi Rich, The "part 2" of the QST article on the WA2EBY amp notes that you can set a resistor pad up for 5 W input to the original 1 W input that WA2EBY's amp is designed for, but you waste 4 W in that pad so the amp is still driven with 1 W and you still get the designed ~20 W out using 13.8 V DC. ?Are you making a more extensive modification to get more power out? (Of course, you can get more out of the amp with 28 V drive, up to 70 W with appropriate heat sinking - see Figure 7 of the Part 2 article available at ). It seems also important to note that the amp is designed for CW/SSB operation only and not digital, because you just can't sink away the heat and not destroy the finals. ?In the thermal calculation section, he writes: "These [thermal] calculations make it clear that the amplifier should not be used for AM, FM or any other continuous-carrier operation. The amplifier should be used only for CW and SSB operation where the duty cycle is significantly reduced." 73 Phil W1PJE |
