Ultralinear and Triode. What's the difference

Philefreak, KT88 and 6550s are tetrodes. The “KT” stands for kinkless tetrode. The screen and suppressor grids are tied, hence being a tetrode. An EL34 is a true pentode.

Running a 6550 in triode mode simply means that the suppressor grid is biased to the anode, normally via a resistor. It does not compromise the working of the working of the tube or the sound in any way. The suppressor and screen grid do not “get in the way” of the functioning of the tube when run in triode mode. Most audio critics/audiophiles prefer pentode and tetrode tubes wired as triodes.

Regards
Paul

The CAT JL2 uses a pentode tube (6550) in triode mode. I don't beieve there was any compromise made in choosing tridoe operation. It is one of the best sounding amplifiers I have ever heard. I suspect that design and implementation may count for more than design topography.

Tvad ; as I stated in my first response , "Sales hype or not ? I don't know ."
Please report here , or p.m. me , with the results of your research . It could be quite informative , in more ways than one !
Thank you .

My my, half-truths and overgeneralizations.

Pauly: Running a pentode/tetrode in triode "...does not compromise the working of...the tube or the sound in any way." I'll agree with the 'working' part, but the 'sound' part I disagree with strongly. I believe most hi-end audiofools would state that true triodes almost always sound better than triode-wired pentodes/tetrodes (P/Ts). That's why virtually no Single-Ended Triode amp is made with KT88s or 6550s or EL34s or any other P/T. The VAST majority of builders and buyers of SETs build and buy them equipped with real triodes such as 45s, 2A3s, 300Bs, 845s, or 805s*. Probably most push/pull triode amps are designed with P/Ts for some reason. Maybe that's because once one departs from the sonic purity of an SET, it matters less whether one uses a P/T or a real triode.

Pauly: "Most audio critics/audiophiles prefer pentode and tetrode tubes wired as triodes." Really? My understanding is just the opposite.

I believe that triodes get the harmonics of the music better than do P/Ts. I'm now on my 2nd pair of mono SETs, this time with high-sensitivity speakers, DIY open-baffle linearrays, and I have NO plans to ever consider going back to tubed amps using P/Ts.
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* The typical output power of these class-A triodes used in SETs approximate 1, 3, 8, 20, and 40 - 50 Watts, respectively. I'm not familiar enough with the PX25 and 211 to state each's typical power output in an SET.
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The term ultra-linear is also called "distributed load amplifier" wherein the sceen 2 of the tube is DC biased from each half of the primary such that the tap point is 43% of the turns ratio or 18.5% of the impedance when measured from the primary center-tap.
Both the KT88 & 6550 are often used in the ultra-linear configuration for power amps because, I understand that, these 2 tubes (not the only ones, mind you!) are physically constructed such that the above mentioned percentages can be obtained. I also understand that the EL34 is a tube made for correct ultra-linear operation.
Technically speaking the ultra-linear amp delivers ~2X the power of a triode amp & about 75% of the power if the same tubes were used as pentodes using the same DC voltages with substantially less distortion.
Sonically, the ultra-linear sound is supposed to be (generalized) "clean, bright, sharp, punchy" sound while the triode sound is supposed to be (again, generalized) "smooth, sweet, mellow, natural" sound.