US PATENT SUBCLASS 330 / 87
.~ Cathode impedance feedback

Current as of: June, 1999
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330 /   HD   AMPLIFIERS

75  DF  SIGNAL FEEDBACK {20}
87.~ Cathode impedance feedback {4}
88  DF  .~.~> Cascade amplifier stages with cathode-cathode feedback {1}
90  DF  .~.~> Combined with diverse-type feedback coupling {2}
94  DF  .~.~> Frequency responsive means in cathode impedance feedback path
95  DF  .~.~> Nonlinear impedance means in cathode impedance feedback path

DEFINITION

Classification: 330/87

(under subclass 75) Subject matter wherein the "signal feedback circuit means" or the "shared impedance of the input and output circuits" or a portion thereof is an impedance between the cathode of a vacuum tube amplifying device and ground or other convenient electrical potential reference plane.

(1) Note. For this and indented subclasses the anode current flowing through the "cathode impedance" develops a variable signal potential on the cathode which, relative to the grid of the same amplifying device is effective as a negative signal feedback in that amplifying device; and which may in addition be applied as a signal feedback from such cathode impedance to another input electrode of the same amplifying device (or an amplifying device of a preceding stage); or to which cathode impedance a signal feedback may be applied from an output electrode of the same amplifying stage or a following signal amplifying stage.

(2) Note. Subject matter involving cathode coupling, such as cathode follower output circuits or where coupling is to the cathode and there is normally no cathode impedance signal feedback as in "bootstrap" coupling (subclass 156, below) or where no signal feedback function is indicated, is not classified in this and indented subclasses but in the appropriate cathode coupling subclasses below such as subclasses 186+, for input circuit network coupling to the cathode and subclasses 193+, for output circuit coupling from the cathode. See the internal search notes under these subclasses for other subclasses of this class involving cathode coupling.

(3) Note. The above requirement of (2) Note, for classification in this and indented subclasses, namely, that where cathode coupling is involved an indication that signal feedback is present in the circuit, applies to all of these subclasses except subclass 89 involving cathode impedance feedback between adjacent stages. Where there is cathode-to-cathode coupling of adjacent cascaded stages classification is in subclass 89 regardless of whether signal feedback is indicated or not.

(4) Note. Subject matter involving a cathode impedance which does not develop a signal feedback voltage but is by-passed in such manner that a D.C.. bias voltage is developed, or due to operating conditions, is disclosed, in the case of a single by-passed resistor, as developing a D.C.. bias there across and not a voltage varying with the signal, are not classified in this and indented subclasses but in subclass 142 below.

SEE OR SEARCH THIS CLASS, SUBCLASS: 70+, for vacuum tube amplifying device amplifiers series energized for power.

78, for signal feedback circuits compensating for inter-electrode impedances to or from a common electrode.

119, for push-pull amplifiers involving cathode coupling.

158+, for interstage coupling to the cathode.

168, for transformer interstage coupling from the cathode.

172+, for interstage coupling from the cathode.

186+, for input coupling to the cathode.

193+, for output coupling from the cathode.

291+, for semiconductor amplifiers having signal feedback means.

297, for semiconductor amplifiers series energized for power.