Sound of GM100 Tube Versus 833 Tube

There are no "sonic characteristics" of tubes that I am aware of. It is all a combination of circuit design and inherent tube characteristics.

For example transconductance defines the differential of plate-current to the differential of grid voltage.
This is highly dependent on the operating point (Bias) of the tube.



All tubes have somewhat different characteristics which are very important while designing a circuit.

Thomas Mayer has a lot more knowledge than I do.

Your question is a fascinating subject Ron, but hard to answer. Although it is not deeply studied, the mechanical structure of the tube electrodes must have some influence in tube sound. In fact it is the main structural difference between direct heated triodes and indirectly heated triodes - the plate cathodes of indirectly heated tubes are much more rigid and uniform than the filaments. Electrons do not know by which type of metal cathode they are emitted - but if the distances between electrodes vary due to electrode configuration, vibration or micro changes of geometry inside the tube due to the signal itself the sound is affected. There is no magic in tubes - any sound difference must have a physical explanation, and just the differences between the plate curves or operation points in tubes are not enough to explain the differences in sound between tube types. Noise per se also can't explain them.

The 833 has some similarities to the 572b transmitting triode in my smaller Wavac. They both are high gain, which means they have 'pentode' type curves rather than the typical triode curves (i.e. voltage vs. current curves), even though the 833 and the 572b are true DHT triodes. The GM100 looks like it has more traditional triode curves.

I am not a circuit expert, but what that generally means is that it is easier to get a linear load line with triode types, whereas a pentode types take more care to linearize and will tend to have more third order harmonics. Third order harmonics don't necessarily have to be bad compared to a preponderance of just second order harmonics, but a lot of audiophiles like the traditional triode/second order harmonic paradigm better and, of course, the better linearity of standard triode curves..

My 572b Wavac golden flaming beasts sound wonderful to me, so whether the differences are more theoretical than practical could be moot..