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Is first-half preamp stage in "CHAMP" a "textbook grounded cathode"?

7/23/1999 4:15 AM
Is first-half preamp stage in "CHAMP" a "textbook grounded cathode"?
as I'm looking at this and TRYING to make some use of this "TubeCad" thing - it looks to me that the first stage in the "CHAMP" schematic (5E1) seems to match the "textbook grounded cathode" circuit in "tubecad"... is that anywhere near right?
7/23/1999 4:35 PM

That stage is in the arrangement referred to as "common cathode", where the input signal loop and the output signal loop both travel through the cathode. Even though it's set up with a grid to cathode biasing arrangement called "cathode bias", with a resistor between the actual cathode and ground, it could be loosely referred to as "grounded cathode", when comparing it to other configurations. Both signals are referenced to ground through the cathode.
7/26/1999 7:12 AM

The cathode is grounded at AC signals because of the cap that is in parallel with the cathode resistor.  
In a small signal modelling we can ignore the cathode components, the res and the cap, when calculating the parameters (gain and impedances) of the stage af the broad frequency (I donīt know if "broad frequency" is the correct term, it means the freq. where the gain is max). This is because at these frequencies ALL the caps are a short circuit to AC signals.  
Later, the caps will be included in the model to calculate the frequency response of the stage.  
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