Triode versus Ultralinear/Pentode

Switching an amplifier from pentode to triode can be a bit tricky inside a single amplifier. The reason is that triodes tend to have a lower impedance than pentodes and so will want to operate at a different impedance on the output transformer.

That is tricky to set up and a lot of amplifier manufacturers 'fudge' that parameter a bit.

Its also interesting to observe the behavior of a pentode wired in triode as opposed to a real triode- it becomes obvious that real triodes have better performance. It is often difficult to demonstrate this fact because there are so many variables that get introduced, but- if you are thinking that triodes might have something to offer, you would be right. One of them is *not* power :)

You use triodes when the best sound possible is your goal. They offer lower distortion meaning little or no feedback is required, and lower output impedance which means less turns on the primary of the output transformer (that translates to: less distortion and more bandwidth and *that* translates to 'more detail, better highs and lows') or maybe no transformer at all.

The trick is like it always is- get the right speaker to take advantage of those advantages. There are high power triode amplifiers but they tend to be rare.

Lloydc, your amplifier might be a good example of what I meant- that even though there is some advantage of the 'triode mode', that mode is not optimized in the amplifier in order to allow for the switching in the first place. Were it optimized, there would be no trade-offs in sonic performance, only power.

Pubul57, Merlins don't need a lot of power. We have had many Merlin customers over the years using our M-60 and I never hear about power issues. If you can get a triode amp that makes at least that much, unless you are in a very big room you should be fine!

With Merlins it all about finesse rather than power- they are plenty revealing- going triode with them will definitely pay off.

Pubul57 is correct. Some amplifiers pull it off quite well- others don't. I rebuilt a Marantz 9 from years ago- the amp sounded OK on Pentode, but really, triode mode was the really useful mode if you were listening seriously. Most triode amps today would eat if for breakfast, though. Its a fact that pentodes wired in triode do not have the same linearity of real triodes.