From: Paul G4KZYSent:
Monday, September 27, 2021 1:32 AMTo: Elecraft-K3@groups.ioSubject:
Re: [Elecraft-K3] K3s IF-Out level
From the data sheet the J310 looks like a reasonable alternative. It has a higher Gate Source Cutoff Voltage than the J309 which suggests that the DC source voltage will be higher than the J309, leading to the source voltage (voltage across R9) going up from about 1.3 V to maybe 2.5 V and the current through the FET and R9 will therefore increase from about 6 mA to about 11 mA. R9 will dissipate more power but it should still be under 30 mW so not really a concern. Q10 is a source follower configuration amp so the voltage gain is (just below) unity and the change in the DC conditions should not materially affect the small signal gain.
I'd be interested to hear how you get on.