I did replace my old BLX15 power transistor with a modern Power MOS device. The BLF177 the BLX15 has 6dB gain only at 70MHz. While the BLF177 should have over 20dB. After a few days trying all I could think of to get stable power out of the BLF177 MOS at 70MHz the result was 2 melted tuning C's. It sure can generate power this device but I did not manage to let it work at the wanted frequency. Many combinations of L and C where tested. The original circuit was used for 50MHz relatively close to 70MHz. I did not expect major changes in the L and C's in use. The 2 stage low-pass filter should be almost the same. Of course the bias circuit is different but simple only a pot-meter to get about 3V at the gate for 500mA. The BLX15 needed the 0.7 PN diode in parallel to get a 500mA bias. I have edited an input file with the scattering parameters from the specification data for RFSimm99 I need a working circuit with practical L and C values to continue.