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In Reply to: RE: What tubes to use with this Interstage Transformers? posted by megasat16 on September 08, 2016 at 09:23:34
The problem with the (FG Z + external series resistor = new FG Z) when the load circuit has reactive component and it will change depends on the AC source. The results aren't the same everytime a signal from the FG increases or the frequency increases or decrease.
this is case with any source with a greater than 0 output impedance. For this particular application it is the fact that the source Z is 5K that we are using to our advantage in order to find the effect of the reactive component (primary L). The variation you speak of is exactly what we are looking for so we can work it against the other knowns to find the unknown (primary L)
dave
Follow Ups:
Dave,
From your theory to work, you will need to the DCR, and either the inductance and the capacitance at that frequency. You also need to consider which is predominant factor (i.e. primarily resistive, or capacitive or inductive). You will also need to consider the phase angle based on the predominant factor. And then, you will need to figure out the amount of reflection to the source. And once you know that, that's the result for the one fixed setting (such as 2Vp-p, 20Hz). Once you change a little value, you are required to recalculate once over again.
Again, the source is the TRUE origin of the current / voltage.
I know what you have been saying all along on this topics. I wish you are right and things are that easy too. But it's not and I learned that very long ago. In fact, all of us (my classmates and I) got it wrong at the very beginning and puts a big smile on the Instructor face. Some good memory there.
Regards,
James
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.Thou shall not stand where I type for I carry a bottle of Certified Audiophile Air and a Pure Silver Whip.
You seem to be completely missing the application here. The ultimate function generator in this particular situation is a tube with an Rp of 5K amplifying the random signals we call music. This is what needs to replicate for a precursory test.
You mention your ideal for a function generator being an amplifier with a feedback loop yet this actual application doesn't meet that criteria so I guess we now need to wrap feedback around our tubes to make them work properly.
Back to the original task, the 5K series resistor will work perfectly for this application. It may show issued in different applications however this is not about designing a universal device it is about testing a very specific application. The main thing of interest is to determine the primary inductance of the DUT to see what tubes it is suitable for loading across the audio band.
dave
Dave,
Please don't start on the topics of amplifiers and feedback? It took me a good part of a year on that subject learning all types. It definitely doesn't serve the purpose of this thread.
The tube with Rp of 5K-10K is what I want to use as a source to test the transformer for an actual bandwidth and FR curve.
I have very little interest in the actual L value or the Z value but a nice HP Impedance Analyzer would be an addition to my toys in the future.
Regards,
James
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.Thou shall not stand where I type for I carry a bottle of Certified Audiophile Air and a Pure Silver Whip.
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