A friend from Canada ordered a pair of boards and I used the opportunity to test the newly arrived hybrid mu-follower (aka as gyrator) Rev08 PCBs. He will be using these boards in the 300B design posted here.
Here is the driver circuit diagram:
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As you can see, I increased the anode voltage to get about 14mA of anode current. This was due to the DUT I had at hand. The protection resistor R8 is set to 150Ω so you just get a slight dim light on the LED under normal operation. It will lit completely under an output short (which likely kill the LED) or under A2 operation (e.g. grid current)
The actual load resistor is 100KΩ which when connected to the audio test interface reflects a total input impedance of 50KΩ.
Here is a test of the frequency response:
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And here is the harmonic profile under 200Vpp swing:
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Nice results, very happy.
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