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In Reply to: RE: I sense a lot of head scratching goin on posted by DAK on June 20, 2016 at 17:43:37:
"So, a concern has been to equalize the gain of each single ended stage."A circuit that consists of two triodes with their plate resistors connected to the same power supply, with one common cathode resistor, with each grid being driven by out of phase signal is a differential amp (diff amp) and it's one differential stage not two single ended stages.
The common cathode resistor causes corrective feedback so the gain in one half is being forced to be the same as the gain in the other. (the feedback at the top of the cathode resistor is negative feedback for one tube, while at the same time, positive feedback for the other)
A CCS (constant current sink), instead of a cathode resistor, improves this action.
Both triodes are forced to operate only in Class A and they are forced to have equal gain (one triode vs. the other).
BTW, in your original post you said linearity and now you say gain.
Gain is just gain, example.....1 volt in.....10 volts out equals a gain of 10, etc.
Linearity has to do with harmonic distortion. A very linear tube operating at a very linear operating point (voltage, current and load impedance) will have very low harmonic distortion.
A constant current source in the plate circuit of a SE stage can help with linearity and gain.
A constant current sink in the tail (the cathode) of a diff amp can help with linearity and balance (matching the gain of each triode in the diff amp). The gain of the diff amp, as a whole, will be determined by the value of the plate resistors and the tube chosen.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 06/20/16
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Follow Ups
- RE: I sense a lot of head scratching goin on - Tre' 20:37:10 06/20/16 (3)
- RE: I sense a lot of head scratching goin on - DAK 20:46:11 06/20/16 (2)
- RE: I sense a lot of head scratching goin on - Tre' 20:58:21 06/20/16 (1)
- RE: I sense a lot of head scratching goin on - DAK 21:12:25 06/20/16 (0)
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