Has anyone experienced problems using an IRF530N in a 500kHz PA?. I am using an IRF530N into an L – C – L  output network the design parameters for the network are input:10 ohms, output 50 ohms, centre frequency 502.5 kHz, Q = 12, giving, L1  38µH, C1 3.7nF, L2  84µH, C1 consists of a 3.3nF fixed capacitor plus a 2 gang 500pF variable, 3mH inductor in the drain. I have tried driving the MOSFET with a 5v positive peak signal, and with a 3v rms signal sitting on a +ve bias, I have managed to obtain 5w into a Marconi TF1152A/1 (50Ω) power meter about three times, but when 12v is removed from the PA and reconnected there is no output, C1 is adjusted for maximum power output, but is never the same position twice, and there seems to be a very critical adjustment of the drive to obtain, a) an output, b) anything that looks like a sine wave, although when I have got it right there is a very good sine wave. Any ideas anyone as to what may be going wrong?

 

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73   Ken Wright   M0KHW    IO91TV