[G0HZU_JMR]

Here's an image of my old Maplin YN48C DIP meter and the schematic diagram taken from the manual. It isn't a very good dip meter but it is a bit different because it uses a BJT in the oscillator section.

If anyone wants to analyse the JFET based neg resistance oscillator then it's best to use the typical data from the 2N3819 datasheet.

Cgs 3pF
Cdg 0.7pF
Cds 0.8pF
gm 5mS

There's enough info there to see how the circuit can develop negative resistance via internal feedback. If you build the circuit then best to use a genuine 2N3819 and not a dodgy equivalent or a chinese ebay version. You could try a 2N4416A as that has tighter specs on the device. Don't use anything like a J310 as the Idss is way too high and the device will run at a high current. It's also got higher internal capacitance. It should also oscillate on a spice simulator but care is needed in setting up the simulation and you need to select a valid spice model for the JFET. There are quite a few dodgy spice models out there.