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In Reply to: RE: PX25 max dissipation?? posted by horny on July 14, 2007 at 01:49:41
Thanks Horny (great moniker !;-), that's helpful information. When you say 390B+ are you stating the voltage on the anode to ground, or the voltage across the tube (anode to cathode)? I assume it is anode to ground.
If the actual measured results don't match PX25 plate curves, it makes it pretty tough to design an amp. I realize it will only be in the ball park on paper, and that measurements and listening will determine the actual op points, but at least it will be close. Perhaps Brian might take an average transductance PX25, and run some curves on his Sophia curve tracer, and make the information available.
Your measured results sound a lot closer to a 300B than a PX25, but I really don't care about that, what I care about is the sound. It is encouraging that you say it sounds many times better than a 300B
My concern for accurate plate curves is because I'm designing a differential amp from scratch. Without reasonably accurate curves I can't design a proper driver stage, and play with different load lines and op points, to see how it effects distortion and output power.
I really don't care if the actual curves match the original PX25 or not. Even Osram put out two different spec sheets, that I could find. The curves weren't the same, and one sheet said max dissipation was 20 watts, and another claimed a max of 30. What I do care about is the sound, and reasonably accurate curves (I realize there will always be some variation).
twystd
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