Ultralinear and Triode. What's the difference

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.

01-19-07: Jeffreybehr "... but the 'sound' part I disagree with strongly."

preference in sound is 100% subjective and as such rather stupid basis for an argument.

"That's why virtually no Single-Ended Triode amp is made with KT88s or 6550s or EL34s or any other P/T."

Really? I happen to own a SE ASL KT88 triode and an acquaintance owns a Art Audio Gill Signature. I guess those two are anomalies? Or perhaps you are the one generalizing?

"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*.

The vast majority of builders and buyers build and listen to transistor amps. Doesn't mean that's to everybody's taste, does it?

"Probably most push/pull triode amps are designed with P/Ts for some reason."

Wow, really? Funny, I own a SE 6550 Audionote wired in tetrode mode which sound just great. Should we call Peter Qvortrup and tell him he is a dummy for designing such an amp?

I must have build about 20 tube power amps and there is nothing that makes a triode more (or less) suitable for a SE application than a tetrode or pentode.

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

Just about every review of an amp with a triode vs. ultraliniar switch, the reviewer has always preferred triode mode. You should try read some reviews.

“I believe that triodes get the harmonics of the music better than do P/Ts”

LOL, they “get” it better, do they? Yep, I am out of my league attempting to argue with my limited knowledge.

“"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.”

Bully for you.

"The typical output power of these class-A triodes used in SETs approximate ... blah blah"

FYI , it is somewhat redundant to say “ class-A triodes used in SETs” as any SE amp has to run class A. Also, there is no such thing as a class A triode. Class A refers to how the tube is used. Any triode can be wired in class A or class B. Thought I'd let you know.

Regards
Paul

"preference in sound is 100% subjective and as such rather stupid basis for an argument" Then why argue? Your vast knowledge is impressive but, your the one that insist upon setting myself and Jeffreybehr straight. All I suggested is that I've never heard a pentode,tetrode(no matter the topolgy) sound like a true triode done class A. It's a sound preference thing that isn't worth argument. Kind of like an analog/digital, tube/solid state thing. I'm just giving my opinion to the original poster. I think that he or she may benefit from my experience. I'm going on my sound prefrenece alone, not a debate over tube topolgy correctness. Not worth an arguement!

Hi Philefreak. My response to you was not meant in any derogatory fashion, and I apologize if it came across as such. (I re-read my response to you and cannot figure why I got such an insulting response from Jeffry)

In my response to you I simply wanted to state that by triode strapping a pentode you do not compromise the tube in anyway, in fact no matter how you configure it, it still runs as a pentode/tetrode.

A pentode/tetrode needs to have it suppressor and screen grid biased to +. There are basically three ways to do that. You can bias the grid from the power supply (pentode/tetrode mode), you can bias them from a center tap on the primary winding of the output transformer (ultra-linear) or you can bias them from the anode (triode mode). Why the latter is called triode mode I am not sure as the tube's suppressor and screen grids still function as designed, and as such the tube is still functions as a tetrode/pentode in every respect.

To your point, a triode strapped pentode is not a triode; not by a long shot. (But I cannot see where I supposedly had said anything to the contrary)

It is however, quite handy to have the triode vs. ultra linear switch as allows you to slightly alter the characteristics of the amplifier. As such you can change it to suit the music you play. Most audiophiles normally prefer pentodes to be triode strapped. Personally I prefer pentode/tetrode mode, but I have rewired a number of peoples tube amps to triode for them.

As for pentodes or tetrodes being inferior to triodes, well that is plain ignorance. Most pentode/tetrode amps have cheap components and cheap output transformers. As such they are unimpressive. However, if you ever have the opportunity to hear an amp like an Art Audio Gill (single ended triode strapped EL34) or AudioNote 6550 SE (single ended tetrode) you'll forget any notion of pentode/tetrode being inferior. They can provide fantastic sound given the right design and components that exceed true triodes in some areas.

“I'm going on my sound preference alone, not a debate over tube topology correctness. “

That makes two of us.

Regards
Paul