Triode vs Transistor

[TheGimp]

Bigun, you capacitively bypassed the triode thereby eliminating cathode feedback. You did not bypass the emitter resistor, allowing emitter feedback. This is a skewed comparison.

Remove the cap from the triode and adjust the input signal to compensate and I would be willing to bet the triode bests the bjt.

 

[Bigun]

The comparison I wanted to make was equal input signal, equal output signal.

 

[indra1]

... perhaps something to do with the higher order harmonics perhaps or non-linear capacitances of the BJT ?

Nelson Pass showed that some depletion mode devices tends to yield lower distortion. Michael J Koster showed his use of the IXTP01N100D on his Schadeode experiment. Simulation such as the one I post on #20 shows that IXTP01N100D also yields very low higher order harmonic components. However, other factor such as SS memory (thermal) distortion described by Peufeu may contribute to aggravate the generated distortion perceived as unpleasant. So operating an SS device at zero tempco point or usage of a zero tempco device such as a SIT JFET like the 2SK82 or SIC depletion JFET like UJN1208K or the elusive SJDP120R085 could make a difference.

Well then, we have BJTs that can be set up to be readily more linear than triodes. So why do we see no feedback SE ended triode amps as being quite common ...

Perhaps measuring distortion of amplification system alone is simply not enough, the investigation should include employed transducers as Total System Distortion as described by Eduardo de Lima in his paper http://img2.tapuz.co.il/forums/1_133166698.pdf. And then there are various other relevant factors such as RFI immunity.