Bob you may want to check your meters.? I just do not see how you can get 25 watts out at 14 volts when only drawing 1.9 amps.? that would be only 28 watts at the most input to the transistors.? That would make it almost 90 % efficient.??
On Wed, May 16, 2018 at 2:51 PM, robert_kross via Groups.Io
<robert_kross@...> wrote:
Good Afternoon,
Finally received and housed my ubitx. On receiving the PCB, I replaced the IRF 510 outputs with IRF 530's. These tend to run a little cooler and are just as inexpensive. I tested the output on 40 meters as it was at 25 watts at 14v drawing about 1.9 a. I also replaced driver transistors Q92,93,Q96 and 97 with 2 2N3553's.? I socketed the drivers so I could plug in various types. You can try 2N2219a but they tend to run a little warmer.? You also want to short the 22 ohm resistors off the emitters. I used Q93 and Q96 as they were furthest away from each other and provided space for a heatsink if needed. Lastly, parallel R961(2.2 ohm) with a 1 ohm 1/2 watt.? Be careful to shield the toroids with aluminum foil when soldering so as not to short them out (like I did). After removing C261 and C262 in the feedback circuit, I came up with at 14v: 27.16 watts at 20 meters, 31.78 watts at 40, and 36 watts at 80 meters. I am running a 7812 voltage regulator for the receive and transmit drive, leaving raw B+ for the outputs.? I am also running a microphone compressor. I have made 2 contacts (one 300 miles away and the other roughly 700 miles away).? Both contacts were impressed at the level of power I was using.? I must have a reasonable attic shortened dipole antenna.? Anyway, the 2N3553's barely get warm after keying up the microphone.? I calculated that the 2N3553's were only driving the outputs with 460mw.? I was planning to drive a linear amp with it, but now I will use it as a stand alone radio.? I have not heard of anyone doing this, so I thought I would throw this one out for consideration.
Regards,
Bob KD9ITL
