Circlotron

The concept was resurrected in its transformerless form in early 1980s by Ralph Karsten, founder of Atma-Sphere, which remains the principal contemporary manufacturer of circlotrons.

Grids of each triode are driven in opposite phases with a balanced, symmetrical input signal; differential current flows through the loudspeaker load and a simple, relatively high impedance, resistor network that ties floating supplies to the ground.

Simple OTL amplifiers, for example Atma-Sphere M-60, employ 8 double triodes of 6AS7 type per channel; each continuously dissipates an average of 30 watts.

Perceived fidelity (quality) of audio reproduction is a hardly quantifiable, subjective measure that should be left to each individual listener's taste.

Circlotrons, unlike minimalistic single-ended amplifiers, need to employ quite complex balanced input and driver stages delivering at least 100 V peak-to-peak voltage and able to drive relatively high capacitance loads (due to the number of paralleled power triodes and associated long wiring).