50 Watt linear power amplifier with IRF510

In many cases needed more power than 5Watts therefore I built a cheap amplifier for my FT817 qrp radio.
I choose the very cheap IRF510 mosfet. The push-pull PA is working in class B mode. The quiescent current of fets are only 20 mA. 2.5 W input power creates 50 Watts output at 7 MHz. I measured lower power at the higher bands but more than 20 Watts can be achived at 21 MHz.

The control board of PA measures the input voltage, temperature and the SWR.
There is a 4 band output low pass filter and an antenna switch for my two magnetic loop.