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Phase Splitters

In a push-pull amp, you need a phase splitter to produce the two identical but in phase opposition signals to drive the power tubes.
Phase splitters are like religions, you belong to one or another and discussions between fans are often emotional.

Contents


Cathodyne

The cathodyne is the most used phase splitter, probably because it's the simplest and yet quite effective.
Examples are nearly everywhere on this site.

Pros:

Cons:

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Long Tailed Pair

This is also a common phase splitter. It is also called "cathode coupled".
Examples at EL84 amp or EL34 amp.

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Schmidt

Two triodes are mounted in a differential. The grid of the second tube is decoupled to the ground through a capacitor.
Examples at KT66 amps or 6550 amps.

Pros:

Cons:

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Cross coupled

Also known as Van Scoyoc. It needs a low output impedance from the previous stage, that's the reason for the transformer in this schematic.

Practically, a transformer is usually substituted by two cathode followers.

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Paraphase

This phase-splitter is also called "anode follower" or "see-saw".
This splitter takes the signal out of the 1st tube, passes it through a voltage divider and injects it into another tube to obtain the inversed signal.
The second schematic is a simplified version that can be used when the following tubes have no grid current.
Example at 6V6GT amp.

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Isodyne

Schematic by E. F. Worthen (August 1958).
Example at EL34 amp.

Pros:

Cons:

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Transformer

The schematic is self-explanatory, each output connection of the transformer has the same signal but in phase opposition.
Example at 6AS7 amp.

Pros

Cons

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