60 years ago saw the introduction of the Western Electric 300A and 300B
direct-heated power triode, RCA 45, 50, and 2A3 directly-heated power triodes,
and RCA 27, 56, 76, 6P5, 6J5, and 6SN7 family of indirectly-heated triodes.
Sixty years later, these devices continue to be the lowest distortion
amplifying elements ever made. No pentode, bipolar transistor, JFET, or MOSFET
has ever approached the distortion performance of mid-Thirties triodes. In
addition to low distortion in the absolute sense, the distortion spectra of
triodes is favorable, with a rapid fall-off of the upper harmonics. (This is
not true for beam tetrodes, pentodes, or solid-state devices, which are
intrinsically less linear.)

If you ever want to put a solid-state designer on the spot, ask them which
transistors were designed for high-fidelity audio applications ... and are they
still on the market, ten or twenty years after they introduced? The sad fact is
that solid-state devices have linearity well down on the list of design
priorities, with feedback needed to clean up devices that were never primarily
intended for audio. The automotive equivalent would be cars modified to use
truck diesels ... OK for Soviet Russia maybe, but do you think you'd want to
buy something like that if you had a choice? Yet this is the state of affairs
in solid-state audio, with the electronic equivalent of an industrial diesel
pressed into service in so-called "high-end" electronics.

Lynn Olsen

Keep the faith - "If it ain't glowing, it ain't going"

=== Andy Evans ===
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