In Reply to: RE: Tube/solid state DIY problem posted by JKT on August 19, 2017 at 16:59:26:
The LND150 cascode is a CCS in series with the 220K resistor. It sets the voltage at 121.3V at the gate of the BFS862. This implies a current of ~0.55mA. This current source can be tested with a couple of 9V batteries and a 10R resistor. Connect + battery to the B+ connection and connect the 10R resistor to the R1/P1 node. The other end of the resistor connects to battery -. Measure voltage drop across the resistor. Should be about 5.5mV. If that is working, it's likely the BFS862 is toast. The DN2540 is a 400V part. If you don't have a jig to test MOSFETs just replace the DN2540. They are super cheap. I use a lot of CCSs and shunt reg. and keep spare MOSFETs and transistors on hand.
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Follow Ups
- RE: Tube/solid state DIY problem - JKT 08/19/1717:22:25 08/19/17 (7)
- RE: Tube/solid state DIY problem - vetmedrobert@gmail.com 09:09:31 08/20/17 (0)
- RE: Tube/solid state DIY problem - vetmedrobert@gmail.com 07:18:34 08/20/17 (4)
- RE: Tube/solid state DIY problem - JKT 10:13:22 08/20/17 (3)
- RE: Tube/solid state DIY problem - vetmedrobert@gmail.com 10:59:59 08/20/17 (2)
- RE: Tube/solid state DIY problem - JKT 12:43:15 08/20/17 (1)
- RE: Tube/solid state DIY problem - vetmedrobert@gmail.com 14:18:56 08/20/17 (0)
- That's really helpful.. - andy evans 02:31:41 08/20/17 (0)