Re: Testing unknown transistors for max frequency response
Another dragon:
Watch out for scope probe capacitance. Your average not rubbish probe has a 12pF load capacitance. At more than a few MHz it's going to look like a pretty annoying resistor in the circuit across collector to ground. This will, with the collector load resistor affect the frequency response in a low-pass fashion. It's worth adding a follower on the output with a known good high fT transistor (2n5179 is a good one if you can get it to stop oscillating) to isolate the circuit from the probe. Also keep the probe ground very short - use the little spring clip if you have one.
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