My WA2EBY Amplifier
After building the WA2EBY MOSFET amplifier exactly according to the project paper, I was disappointed to see only 5 watts output. I had biased each IRF510 at 100mA, used a clean 13.8V DC bench supply, and even tried 19V. The current draw was over 2 amps when keyed,that told me something was wrong. I checked the input attenuator pad , it was built correctly. I used an oscilloscope to verify the signal splitting and combining, and both looked fine. All the transformers and cores followed the recommended turns and materials. I even removed the T/R relay and connected directly to a 50 ohm dummy load to eliminate any T/R change issues. Still only 5 watts.
I started to suspect a shorted turn in the output transformer T3, because high current with low output often means the power is being wasted in a shorted winding. But before rewinding the toroid, I decided to double‑check my measurements. I built a simple RF probe and measured the voltage at both MOSFET drains during key‑down. To my surprise, the voltage swing was healthy,about 13 volts peak. The RF probe was telling the truth, so the amplifier was actually producing the expected RF voltage. The problem was not the amp; it was my power meter. I swapped the meter for another one, and suddenly I saw 25 watts output with only 1 watt of drive at 13.8V. The current draw still looked reasonable, and the MOSFETs warmed up normally without overheating.
In the end, the amplifier worked exactly as designed. The lesson I learned is never to trust a single cheap power meter , many inexpensive "through-line" wattmeters (especially older CB-style or low-cost HF meters) are notoriously inaccurate at lower power levels or can present a poor SWR to the amplifier output. always verify with an RF probe or a second instrument. The WA2EBY design is solid when built carefully.
With the amplifier now delivering a solid 25 watts, my focus has shifted to the next crucial steps: building an RF sampler to safely monitor the output with my PC-based oscilloscope and constructing low pass filters (LPFs) to clean up the signal for 40m and 20m operation.Then move on to the exciting phase of over-the-air testing. It's immensely satisfying to see this project come together, moving from a bench full of components to a practical, on-air amplifier.😎
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Mind storm ideas for Manhattan style circuit board ..
Before installing the MOSFETs, I had already done a clever test. I connected an oscilloscope and a signal generator to the input, then temporarily jumpered the gaps between the gate positions and the drain positions using 0.01µF capacitors. This let the RF signal pass through the entire path from the bifilar split input transformer, through the gate and drain pads, into the combination output transformer with its DC bifilar choke, and finally to the output. I probed the two gate leads and saw identical amplitude signals with a perfect 180‑degree phase difference. I then moved the probes to the two drain leads and again observed the same balanced, out‑of‑phase waveforms. Finally, I checked the output transformer secondary and confirmed that the combined signal was clean and symmetric. That test proved my splitter and combiner were working correctly before I ever soldered in the IRF510s.
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A short clip with bad focusing and shaking picture frame 😁😂
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