My first impression : High quality PCB ( 100 x 50mm ) , all parts in the kit including 2 power FETs type IRF530N. Capacitors are 10nF instead of 100nF as shown in the schematic but that's not a problem.
However i had doubts about the claimed 70 Watts output at 13.8V for these fets are normally fed with 24 - 36V to get a good modulation. The 0.5 turns windings are on the PCB by means of the tubes inside the toroids. Construction is easy but a lowpass filter for each band is mandatory. I used the low pass data from W3NON for a 7 element Chebyshev with standard value silver mica capacitors and T68-6 toroids. The provided wire for the power chocke ( 2 turns ) has a weak coating . It's better to replace it to avoid shortcuts .Start soldering the small parts and end with the transformers. Turn the potentiometer anti clockwise and slowly adjust the bias to aprox. 3.7V.
The test was in the original configuration at 13.8V and 5Watt FM input from my FT-817. Max. power was 80 Watt . At 2.5 Watt input the output was about 50 Watt at 20m.but the modulation was as expected distorded in ssb mode at the recommended 2.7V bias voltage.
At 3.7V ( gate ) bias the modulation is verry acceptable. For the best modulation the FETs can be powered with 24-28V by means of a Step-up converter and a small mod of the PCB. Turn the potentiometer fully anti clockwise and set the bias carefully at 300mA through the FETs at 28V. The 150 Ohm resistors over the FETs heat up strongly at full power FM. It's better to reduce the drive power to 2 Watt when working FM/AM . Don't reduce the drive by reducing the Bias voltage for this results in a distorted modulation in SSB mode. Better use a power attenuator : Power att. calculator PA1B
Unfortionally the seller often forgets to add the documentation. I made a copy of the pdf file . Click on the schematic to enlarge.
A You Tube impression by KC2IRV : Overall impression of the amplifier
Testing the PA
Conclusion : This is a nice kit with acceptable results for a low price.
|click to enlarge|
|150 Watt 12 to 28V step up converter for $ 2.50 on eBay|