The DRD (direct reactance drive) isn't a new concept. The Welborne DRD design is actually a derivation of an old Loftin-White direct coupled design. Granted, Jack Elliano of Electroprint and Ron have made some adaptations, but the basic design concept is still in tact. The DRD concept is to directly couple the driver tube to the output tube.
The Terraplane is the same basic design as the DRD with a few notable upgrades. Ron has (almost) completely redesigned the power supply adding more filtration for an even lower noise floor. He's also eliminated many of the electrolytics within the amplifier.
As you can see from the schematic, there is exactly one passive component in the signal path, one resistor on the input. After that, there are just two tubes (the driver and output tubes), then Jacks custom wound output transformer. This is about as close to straight wire as you can get in an amplifier.
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