Triode vs. Pentode

Zaikesman and Trelja, this has been one of the most informative posts I have read - thank you. What determines which non-triode amps can be converted to Triode mode?
For example, Joe has told me that the Jolida 502B can be.

Hello Springbok. Most commercial push/pull tube amplifiers can be wired for triode output. Another great post here Zaike and some interesting observations. Depending on the type of output tube used for comparing each mode can also have an influence on your observation here. Example:observing the change in the sound of an amplifier employing a KT-88 output tube [beam power tube] when switching from ultralinear mode to triode mode may or may not be consistent with your analogy when the amplifier employs an el-34[pentode]output tube, not to mention the power factor or speaker load the amplifier is reacting to. The quality of the transformers and the amount of negative feedback employed in the output stage will be a major factor and will have a large influence as well.

Yes Ecclectique, everything probably matters as usual, and I don't want to draw too broad a conclusion from the limited evidence at my disposal. (BTW, in my previous post I mis-wrote something: it's the VTL's output transformer that's designed to account for the power tubes' combined output impedance of course, not the power transformer.)

It does seem logical that there may be some advantage in using a beam power tube in particular wired for triode, or at least maybe as compared to a real pentode wired for triode. Makes me wonder if there's ever been a pure beam triode tube designed? But I can't speak to these musings from experience, because I've never had a power amp that used either pure triodes or triode-wired pentodes in order to make comparisons. Maybe Jkaway is in a position to comment on the relative merits between running triode-wired with beam tetrodes vs. true pentodes (although again, there might be a power differential there that could act as an additional, confounding variable in the auditioning results).

However, I did notice during my experiment last night with the 2/3 tube removal, that my monoblocks now sounded superficially much more similar to the stereo amp they replaced a couple years back, a C-J MV-55 that used one pair of Ultralinear-wired EL-34's per channel, good for about 45w. A lot of the ostensible improvements I achieved when I switched to the VTL's reverted to somewhere nearer the old sound of the system, now that the mono's were running in triode with only one pair of tubes per channel for a calculated 30w or so (and despite that the mono's still held a big advantage in the power supply and output transformer sizes). How much of what I originally heard when I replaced the modest C-J with the brawny VTL's was due to things like the beefier power supply and output transformers, and how much simply to the increased output power capability as such?

Springbok10, one consideration I would like to raise for the ability to convert an amp from ultralinear to triode is the reduction in power. While I went out of my way to say I wasn't worried about it, for a lot of amps, it would be an issue.

And, to contradict myself, although my Granites CLEARLY sound best in triode, the Jadis you are now in ownership of, and running in ultralinear mode, beats the Granites handily in every area outside of power. Forget about all of the adjectives I used when I spoke of triode and pentode, the Jadis powering my Coincidents simply played the music as perfectly as I have been lucky enough to hear. And, in the end, that is all I really care about.

Zaike .A very good question,and your guess is as good as mine here. The little CJ is a honey of amp and is always very engaging with the right speaker. I used a CJ mv52 for many years with the roger ls3/5a or the original proac response 2, sold it to a good friend whereby I do get to revisit it regularly and still very much adore the sound of it, it's like seeing a good friend after a long absence. What I find very intriguing regarding the sound of different output tubes and the output configuration in which their wired...... Have you ever heard the CJ with the KT77[beam power tube] output tubes in it? Quite the contrast from the el-34, and it elevates the amp to a whole higher league in every parameter! particularly the bass response. Sounded like a much more powerful amplifier than it's 45 watt spec would suggest. Unfortunately.... a quad of strong Genelex KT-77's will cost you more than the amplifier itself,and that's if your lucky enough to even find them. My VAC pa-90 monos can be configured to operate with 4 el-34's or 2 kt-88's in both ultra linear mode or triode mode with the flick of a switch.I much preferr the amplifier in triode with the el-34 tubes in it, however... when the kt-88 is employed I do prefer the ultra linear setting. The most intriguing thing about this is: Regardless of what mode I choose when the KT-77's are employed in the vacs, they raise the bar to a higher level regardless of power rating.Funny as it may sound.... when the amps are in triode with the kt-77, they sound more powerful than the 90 watts of ultra linear of the el-34. Go figure!