Triode mode vs pento mode

Atmasphere, "the original patent shows that if the tap is correctly placed, you get exact triode linearity with 90% of pentode power."

The industry has chased this promise since the 1950s. If the patent Ralph referenced is the same as I'm thinking, it was filed by those who formed Dynakit; their own products (and I'm a devotee), which obviously had full use of the technology, certainly missed out on realizing the aforementioned claim.

At any rate, since the early 1960s, high-end audio more or less abandoned pentode operation. During "the age of progress", so many entered into building UL amplifiers for nothing more than to put forth ad copy deemed required to keep themselves current.

Most of the time, those in this hobby who mention pentode actually mean ultralinear...

I am guessing the less resolution in triode mode that Dover mentioned only occurs when the triode switched amp is playing a rather loud and complex passage.

Based on my limited experience, to get the best out of a triode amp you really need a very beefy driver stage that does not wimp out. UL has a bit more gain, so to do apples to apples comparison with the same volume you need to drive the gain stage a bit higher and therefore the driver stage would have to swing more voltage.

I have modded a few pcs of gear myself switching them from Pentode (Audio Research D115ii) or UL (Jolida 502) to triode and each time I ended up reconfiguring the driver stage with a much beefer tube such as 6H30 or ECC99 instead of 6FQ7 or 12AT7 and run a lot more current in the driver stage.

Hi Trelja, seems to me Dynaco was one of the companies that got around the patent by moving the tap.

Dover, The problem with going to triode mode on an amplifier like the Dyna MkIII is that the load impedance has to be set up differently- essentially you need a different output transformer if you are to really get the performance out of the tubes wired in triode. I got started in this business by doing mods on Dynaco gear; the above reason is why I don't wire their amps in triode.

Now an amplifier with a switch is hopefully a different situation- 'hopefully' in that the output transformer is optimized for best performance in both switch positions.

Hi Ralph, what about pentode amps like an audio research d115 which is regulated screen grid not UL?
Are those trannies not good for triode too?

Johnsonwu, only if they are properly designed for it. Pentode mode operates at a higher impedance than triode, so the transformer needs to be designed to allow that. IOW you can't just convert an amplifier by rewiring the output tubes in triode mode.