Today did last modifications on the U3S. Installed 3 off BS170 devices and replaced the L1 with bifilar transformer. For more info see QRP Labs technical info . Additionally installed switch for 12V or 5V for final transistors. Bias setting is set to 2.2V for “save” power and a clean output. I got following output:

28MHz – 12V – 560mW

21MHz – 12V – 980mW

14MHz – 12V – 630mW

7MHz – 12V – 1.45W *transistors are very hot

7MHz – 5V – 690mW

3.5MHz – 12V – 1.84W *transistors are very hot

3.5MHz – 5V – 870mW

View on L1 – bifilar transformer

C5 10nF – installed on underside

The box is closed and U3S running very nicely.