Amplifier Update: Now Using an IRF630
December 3, 2010 1 Comment
I couldn’t figure out exactly what went wrong with the amplifier, so eventually I decided to try to replace the MOSFET with a more resilient one and hope it won’t explode like the first one. I know that I need to add SWR protection, and perhaps to improve the T/R switching, but I don’t have time to work on these right now. I hope that the more resilient MOSFET would be able to survive the conditions that caused the IRF510 to explode.
I replaced the IRF510 with an IRF630. The IRF630 has a 200V and 9A rating, so it will be hard to destroy with a laptop 24V supply. The trade off in power MOSFETs is between improved rating (voltage, current, and on resistance) and input capacitance. The IRF510, with a 100V 5.6A rating, has 195pF input capacitance; the IRF630 has 600pF. This makes the IRF630 harder to drive. I had experience with another amplifier, an experimental class E amplifier, in which the driver chip could drive an IRF510 but not an IRF630. I was not sure that the 1W of the Softrock Ensemble would be able to drive the IRF630.
I soldered the IRF630 into the circuit anyway, connected the amplifier to the Softrock and a dummy load, and tried it out. Success! The IRF630 delivered about the same amount of power that the IRF510 did.
I then connected the amplifier to the “unusual” loop and ran WSPR on 14MHz. As expected, there was a significant difference between the signal reports I got with and without the amplifier (and also in the number of stations that heard me). I left the setup running for most of Friday. At the end of the day, the amplifier’s signal was received all the way from Sydny, Australia, through Singapore, India, and Europe, to the eastern United States. Not bad at all. And so far it has not exploded 🙂