My Thunderchief doesn bias correctly at Q3. What should I do?
The third stage of the Thunderchief models one half of the Phase Splitter stage of the amp. The relatively high amount of resistance between the source and ground can do strange things. We suspect that this is a result of the internal resistance between drain and source and what voltage goes up the 1M and into the gate. We know that putting voltage on the gate of a JFET causes the resistance between drain and source to change. This is part of the reason why this stage is critical to the circuit and so hard to bias. Although we’ve built 3 or 4 of the Thunderchief and have not experienced any difficulties, we’ve heard from builders who describe the above issue. Here’s a fix for anyone using different transistors or if they can’t get the third J201 to bias properly: Find the 470/4k7/4k7 resistor chain going from Q3 source to ground. Reduce the first 4k7 to something smaller. Try 1k, then re-bias to half the supply voltage at the drain. This should allow the stage to work properly. Why doe
