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OTL = Output Trasformer Less Tube Amplifiers

My consideration on problems of each design:

Ciclotron balanced design problems (type 1):

more high output resistence because there are 2 device in series
the duplication of the power supply (2 for each channel)
impossible to use with earphone (because no ground on output terminals)
you can destroy the loadspeakers if you don't use a DC protection
(a simple variation of the bias of one output tube will give high DC on output)

Technics design problems (type 2)

changing the load the first feedback cannot to compensate asimmetry of the output stage.
(in the real case the loudspeakers is not a constant impedence)

SRPP (type3)

Futterman design (type 4)
At this time I don't have found problems.

Follows a circuits gallery of new design

Old design circuits

Understanding OTL design in the article Background and OTL Circuits by aria

Understanding Basic Circuits by Atma-Sphere

Commercial OTL Graaf GM-200

Fourier Panthere

Atma-Sphere

Trascendent Sound inc