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Plate Follower
This circuit is used in place of a Cathode Follower. It, like the Cathode Follower, boasts a low output impedance, wide bandwidth, and low distortion. Unlike a Cathode Follower, it does invert the phase at its output and it can have a gain of (or greater than) unity. One of its key advantage is that the cathode potential is close to that of the ground, thus making the heater-to-cathode voltage limit less of an issue.
Textbook Plate Follower
Compound Amplifier and Plate Follower
Current Sourced Plate Follower
Transformer Coupled Plate Follower
Split Load Phase Splitter
Although much maligned, this phase splitter actually sets the standard for balance. As long as the plate resistor equals the cathode resistor, balance is pretty much assured. Nonetheless, this circuit is criticized for not having any gain, clipping sooner than the alternatives, and having dissimilar output impedances on each phase leg. The first objection is certainly true, but then gain is not always necessary and can be a liability in an amplifier without feedback. The second objection is equally true, as these circuit can swing only half the voltage of a Long Tail Phase Splitter. This is so because the triode sees one phase's voltage swing at its cathode and the phase's voltage swing at its plate; whereas, the Long Tail Phase Splitter's triodes see only voltage swing at their plate. Still, maximum voltage swing is not always a necessity; particularly if this circuit were to be used as the first stage in a power amplifier, which is in many ways the best place to use it, as its low distortion and excellent balance would well serve the remaining balanced portions of the amplifier.
Textbook Split Load Phase Splitter
Direct Coupled Split Load Phase Splitter
Equal Zo Split Load Phase Splitter
Constant Current Source Split Load Phase Splitter
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SRPP Amplifier
Very hip, very popular. This amplifier type has many names: SRPP, Mu Follower, Cascoded Cathode Follower. This compound amplifier works by using the top triode as both a cathode follower and a current source for the triode below it. If the cathodes resistors are carefully chosen, true push-pull functioning can be achieved. The positives: high gain, good PSRR, low Zo, one current path. The negatives: high cathode to heater voltages, phase inversion (could be a plus).
Textbook Totem Pole
Self Biased Totem Pole
High Gain & Low Zo Totem Pole
Symmetrical Totem Pole
White Cathode Follower
Earlier, we said the that the Cathode Follower is the work horse of tube circuits, well then this must be the Clydesdale. This buffer circuit offers a truly low output impedance, an almost unity gain output, and a near symmetrical push-pull current swing. How? Feedback from the plate of the top tube is the answer.
Textbook White Cathode Follower
Split Rail PS White Cathode Follower
Constant Current White Cathode Follower
Transformer Loaded White Cathode Follower
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