To build our new RIAA amplifier we bought a batch of 2SK170GR JFET's on eBay. The JFET's arrived, looked fine, we matched them with a GM328A component tester and put 4 JFET's in the amplifier and was ready for the first listening test. The test went terrible wrong, there was absolutely no amplification in the amplifier and it didn't perform well at all. We then measured voltages in the circuit and around the JFET’s the voltage was totally faulty. The JFET’s was de-soldered and put through a more comprehensive test which they failed! This could not be genuine 2SK170GR, we expected an IDSS current between 2,6mA and 6,5mA with gate connected to drain (ground) and 10V between source and gate/drain, instead we observed for example 13,5mA at 1,57V. We then looked very closely at the JFET’s and discovered that the surface looked grind and actually it was uneven. So the lesson learned from this is that if your construction doesn’t work check if you have build it with counterfeit components especially omitted rare parts.
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