2019-04-29 Center Tapped Voice Coil And OTL Circuit

from FB group Vintage Transistor Radios Apr 29

Robert Abend
Yeah, thanks for bringing that up. Many of the GE radios have a center tapped coil in their armature speakers. I never really thought about the unusual CT voice coil. The most important reason why is that a voice coil moves and has to be light to maximize the frequency response. The reason for center tapping is to eliminate the output transformer. But the primary of the OT has higher impedance, which means many turns of fine wire. That’s more difficult to make light and difficult to wind on a piece of thin paper. That’s why the armature is used – it’s much easier to wind.

But all this was made moot by the complementary symmetry OTL ‘totem pole’ circuit, which drives lower impedance loads. By the 1960s this was very common in audio amplifiers. No output transformer, so manufacturing cost was lower.

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