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Single Ended Triodes (SETs), the ultimate tube lovers dream.

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RE: This long thread just tells me what commercial SETs aren't....

Maybe we better define filament bias-- what supplies the bias
voltage in your example? Then one could comment...

Also, are you aware of the tremendous sonic benefits of self-bias
VS fixed bias?

No fixed bias amp has ever reproduced music in a convincing fashion because the bias doesn't vary according to musical demand.

All fixed bias amps sound to me exactly that-- FIXED, not effortlessly flowing as the music is changing.

IF your idea of filament bias includes a power supply for the filament bias, then that power supply is a distortion injection machine, and those effects are easily audible on Hi-Eff speakers.

Biasing using a bias supply (1) doesn't follow musical change well, and (2) is commonly used by salesmen to force tubes to operate at high power,
allowing greater power-per-dollar.

Since this max. power level is forced by fixed bias, tubes can be operated close to breakdown, but never go over that limit.

This is a case where more watts equals MUCH less ability to drive a
speaker that has ever-changing musical requirements.

One place where old practices and texts were actually right is when
it was noticed, long ago, that self-bias amps greatly outdrive fixed bias models at up to twice the rated power. Jadis (France) took advantage of that and sold a lot of amps in America at lower watt ratings. That bias knowledge was once common, but was conveniently buried as watts-per-dollar became THE sales game.

Eventually triodes lost out to pentodes, then tubes lost out to Solid-State. Why? More advertised watts cheaper. Even before solid-state, the game was afoot-- sales people were learning how to get bigger numbers out of tubes.

Self-bias simply outperform fixed bias amps, but there is a cost:
self-biasing using capacitors and a resistor demand a wide-band
capacitor response. No SINGLE capacitor is even remotely capable of providing this.

And--- that is why we spend money on very carefully engineered
capacitor bypassing and tuning. It is an attempt to get capacitors
to actually work musically.

Since self-bias is superior sonically, the focus falls on the
cathode-bias caps. I'm sorry, but this is the best way to get
an amplifier to talk music, and it costs money whether people
like it or not.

-Dennis-



Edits: 09/03/17
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