I'm surprised that the IRF540 is working as a good replacement for the original IRF510.
The IRF540 has a significantly higher input capacitance (1700 pF) compared to the IRF510 (180 pF). From what I've read, higher MOSFET input capacitance requires higher drive levels. Also, the IRF540 is slower to respond than a IRF510.
I wonder if the IRF540 has decreased the transmit power?
Maybe Adam can comment on this.
---In CHINA_QRP@..., <vk2aor@...> wrote :
Hi John and all
Also my local supplier did not have the original FET but a higher current rating and seems to work well. (IFR-540)