A valve amplifier without the need of an output transformer was a dream that had began sometime in the 1930s. The inherent problem of output transformer-less (OTL) amplification though, was that valves were high voltage, high impedance devices, and speakers were low voltage, low impedance devices - hence output transformers were essential components, needed to match the amplifier impedance and voltage to the hi-fi loudspeaker. But output transformers added coloration and distortion.

Julius Futterman, like many young American radio hobbyists in the early 1940s, was involved in war-time electronic development. After the war he became obsessed with OTL amplifier design, and in 1954, patented the first successful OTL circuit.

However, there were penalties to be paid because his design was overcomplicated and inefficient in terms of energy input to power output ratios. The relatively complex Futterman amplifiers had inherent problems - like low output power and a fairly high breakdown rate. The OTL technology was further improved by fellow New Yorker Harvey "Gizmo" Rosenberg, who, under the banner 'New York Audio Laboratories' succeeded in bringing more refined, more powerful variations of the Futterman circuit to the high fidelity purists

Futterman continued designing and hand-building vacuum tube amplifiers under the name 'Harvard Electronics' for a very small and very patient clientele up until his death in 1979, always convinced that tubes simply sound better than transistors.

The Futterman H-3 was one of Julius Futterman's first commercially produced (OTL) amplifiers, marketed under the name of Harvard Electronics.

Hand-made by Futterman in small numbers, these highly prized collectors items are quite rare today and insufficient data is available to place a current value on them. Many aficionados have modified the circuit to make them more stable and reliable.

See the vintage test report for more information on this extremely unique and innovative amplifier.

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