Quote:
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Originally Posted by regenfreak
If slope of the phase/freq plot = group delay, it should have unit of degrees per unit Hz.
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The
phase is represented in radians, not in degrees. Also, the frequency
omega is understood as 2*Pi*f [radians/second]. So the derivative of slope will have the unit [1/Hz] = [s].
Quote:
Originally Posted by regenfreak
The attached photos show that one of the weirdest oscillation waveform that I have come across from an oscillator! Before I replaced the EC81 by ECC85, the EC81 develops instability and crazy harmonics at normal plate voltage of 90-100V. I had to drop the plate voltage to 17V before the EC81 produces stable output. The valve was running at space charge voltage! I dont have an explanation for this. Maybe EC81 is a "hot rod", excitable valve or the oscillation coil couples inductively with the 5 other resonators before i installed the shields. I used silvered plated coils and the 6-gang variable capacitor are also silvered plated so the unloaded Q of the LC tank can be quite high.
At the moment, I get excellent stereo fidelity and sensitivity with the 6-gang tuner even it is not yet properly aligned.
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I would suspect, that the triode in the LO circuit, with its inherent Ca-g capacitance prefers to look at the 3uH at its anode as the perfect candidate for a Colpitts oscillator, ... and here we go.
So you should probably switch to Colpitts from the start.
... But now, if I see right the anode blocking capacitor to be of leadless type soldered directly to ground plane, I take back the explanation.