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RE: What tubes to use with this Interstage Transformers?

OK...

Set my signal generator to 20hz and a 30V peak-peak signal (maximum output)

measured the FFT of just the waveform into the scope and got this:





I then placed the primary of a 10K:16 output transformer in series with the 50R output impedance and put the scope probe across the 16 ohm load resistor. I then inserted a 5K series resistor with the output of the generator and here are the two FFT's

green is the 50R out and Blue is the 5K50 out.





The loss in amplitude is expected from the finite inductance working against the 5K source but for the most part the distortion remained unchanged.

To keep this complete I also ran frequency sweeps from 1hz to 1Khz with both the 50R and 5K50R source impedance and a 16R load and got the following two sweeps.





again as I stated, the higher source impedance readily shows the results of a finite amount of inductance of this transformer which brings us back to my original point that a sweep of a transformer with a 50 ohm source impedance is pointless unless you intend to use it that way in circuit. Your mention of using a 10 which has roughly a 5K source impedance made me point out that it would be wise to repeat the sweeps with a more appropriate test setup.

I still have no idea what you are referring to about increased distortion and how distortion is even relevant to this discussion but I did what you asked and now it is your turn to repeat the frequency sweeps with a 5K series resistor so we can get a realistic idea of how this device really behaves.

you don't have to take a million data points... Just start at 1Khz and then sweep down to the -1dB, -3dB and -6dB points and that will tell a lot.

dave

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