Futtermans like high impedance and were designed for 16 ohm and above speakers. These were very popular in early hi-fi. Will work OK but the low limit is 8 ohms. They are much more efficient the higher the impedance. Never heard of them taking out output tubes. A very novel tranformerless design.
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Early ones had stability issues. http://www.atma-sphere.com/Resources/OTLs_Defined.php Reading more, it seems JF improved the circuit and fixed the issue. |