300b lovers

You want a technical presentation, here’s my talk at the 2004 European Triode Festival:

2004 ETF Presentation

As for the lengthy previous post, I am not sure about the impact of dynamic variations in output impedance. One way to measure the impact would be to measure distortion harmonics at a constant voltage output, compare 4 and 16 ohm loads, then repeat again into a reactive loads.

The key point stands: Push-pull Class A triode has the most linear interface to loudspeakers. Nearly all loudspeakers generate significant back-EMFs, which are resonant in character, that reflect back into the output devices. Other topologies have nonlinearities or discontinuities that interact with these resonances, which exaggerates speaker coloration.

There are planar-type speakers that present essentially resistive loads, but the reason for this flat impedance curve is very low magnetic coupling between the diaphragm and the magnetic system. As the magnetic coupling (BL product) becomes more intense and efficiency increases, resonances appear in the impedance curve, as well as smaller narrowband divots that reflect stored energy. Regrettably, speakers are inherently resonant, particularly as efficiency goes up. It has to be kept in mind that most speakers are stupendously inefficient, ranging between 0.3% and 1.0%.

@lynn_olson 

FYI,  the guy who published DH tube comparison more than 20 years ago uses the same driver and same speakers as well the same signal source during his blind listening tests.

I can confirm his report that PX25's bottom is much solid and deeper than 300B. 300Bs could not even match 7A1's deepness.  The common sense is 300B could not be driven into A2 region w/o distortion, so I consider 300B is a good candidate for pre-amp/headphone amp which always worked at A1 region.   Also, the measurements of output impedance from 300Bs is way higher than PX25s.  FYI, my 6336 SE amp beats my 300BXL (beefed up 300B) amp hands down at bottom spectrum.

You are right about driving stage quality is the bottleneck of MOST commercial SE DH amps.  but the reason is not what you stated.  The real secret of making best SE amplifier is to SHUNT REGULATE POWER SUPPLY for the driving stage. Push Pull amps are less critical of regulated power supply for its driving stage.

Many roads lead to Rome...

As to DHT shootout, using the same driver may suit certain output DHT tubes better than the other ones. Different DHTs also need different output transformers, different B+ voltages and filament supplies, etc. So AB test is not that easy as more than one elements have to be changed for each DHT output tube to have a chance to perform at its best potential. That said, there is no bad DHT in my personal view - assuming adequate power output. So, many good choices are around!

Don,

Oh my, I was not aware that I had the good fortune to be the first in line for the mono's, but I do recall that I was a very early owner of your first preamp as well your DS2 preamp, both remarkable preamps.  I am gratified to see revealed on this thread the thinking that went into the creation of these stellar monos and the collaboration that brought it about.  The participation of Ralph and other knowledgeable audiophiles, along with Lynn for sure, has given us all an appreciation for the bounds of your joint inquisitiveness that has wrought such a stellar component.  Obviously, it like nothing I have ever heard before, just as you said it would.  The Spatial Triode Masters (which you encouraged me to buy nearly 6 years ago before you yourself had your own pair which was a stellar recommendation as all owners of them know) sound amazing with your amp and my soon-to-be-delivered Cube Audio Jazzon speakers clearly will love to be driven by your monos so expect a report back on that soon.  

Finally, as others have said, this has been among the most informative and civil threads I have ever participated in on the forum and I am among many who are excited to hear your room in Seattle next month.  

This place needs more info like this, I almost resigned sludging through some pretty pathetic posts that all went south and should have been erased.