Julius Futterman
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Julius Futterman (? - 1979) was an American electronics engineer who designed a valve amplifier that did not have an output transformer. This was originally done to reduce costs, as output transformers can be rather expensive. Output transformers also have a reputation for coloring the sound and some enthusiasts came to believe that the OTL design offered better sound.
[edit] Design
The design was initially made in 1954 and came to represent Futterman's belief in the architecture of the 'OTL' (Output TransformerLess) amplifier. The Futterman design was the first commercially viable OTL amplifier. Futterman's design evolved over the years as bigger and better power tubes are created by tube manufacturers to address the increased needs of color televisions. The earliest amps used 12B4 power tubes, which were originally made for tube car radios. The last versions of the amps employed 6LF6 tubes, the largest and most rugged horizontal output tube made for TV use.
Futterman's unique position as a designer of tube testing apparatus gave him unprecedented access to new tubes as they were created. He then applied them to his ever-evolving amplifier designs. Despite internet hearsay, these amplifiers were actually quite stable when used properly and with speaker loads which complimented their design. Most amp failures were tube related or caused by improper use of the amps. The design did not have the duty-cycle for extended clipping nor high power bench testing.
Although some early versions of the circuit had entered small scale production, it was not until Futterman's death that Harvey Rosenberg took the design into commercial production.
[edit] Harvey Rosenberg and New York Audio Labs
After Futterman's death Harvey Rosenberg formed New York Audio Labs and took the design into commercial production. Engineers Ted Hammond, Jon Syder, and Andy Fuchs worked with Rosenberg's New York Audio labs to bring Futterman's H3-AA design to commercial production. The hand wired Futterman samples were converted to circuit boards by gifted circuit board designer Ron Uzzo who had previously designed boards for high frequency transmitters and VHF equipment. The circuit's wide bandwidth design made circuit board conversion an arduous task. Numerous prototypes were made and compared to Futterman's hand built examples for sound, stability, and repeatability.
Rosenberg's company benefited from the introduction of the Quad Electroacoustics ESL-63 speaker in 1981. The ESL-63 is considered one of the greatest speakers ever created, but did have some quirks, including an odd and variable impedance. OTL amps gained a reputation of matching well with the legendary ESL-63, and NYAL sold many OTL amps to ESL-63 owners. While NYAL is now out of business, several new models of electrostatic speaker based on the Quad ESL-63 have been produced by Quad Electroacoustics since 2000: the ESL-988 and ESL-989.
Rosenberg died in 2001. After NY Audio Labs closed:
- Jon Syder returned to school in California and Alaska, now has his doctorate in biology.
- Ted Hammond worked for Verizon, retired, and now consults to various manufacturers in the tube field from his offices in New York.
- Andy Fuchs operates owns and operates Fuchs Audio Technology, a respected manufacturer of tube guitar amplifiers in NJ.
