Triode mode vs pento mode

Al, I wonder if you might be aware of the patent that was originally issued on the ultralinear technique?

To get around it, a good number of companies simply moved the tap. However, the original patent shows that if the tap is correctly placed, you get exact triode linearity with 90% of pentode power. Seems to me this would obviate having a switch.

The funny thing is, the patent is long expired, but so many companies did the work-around (which only approaches triode linearity) that many people (including designers) simply think that thats the way it is!

Thanks Ralph. No, I hadn't been aware of any of that. So by designing in accordance with the principles defined in the expired patent, it is possible to achieve triode linearity with a pentode, while at the same time reducing the power sacrifice to insignificance.

And the reason that approach is often not utilized is simply that designers are unaware of it.

Fascinating, but I'd have to say not surprising!

Best regards,
-- Al

Atmasphere - I would be interested to know if the design if the output transformer will influence whether one way or other is preferable. With both Air Tight ATM3's ( 6L6's ) and Dynaco MkIII's ( EL34's, 6550's ) I prefer ultralinear to triode. In both instances the triode mode loses resolution and screws up the natural harmonic structure. Would this be that the trannies have been optimised for Ultralinear ? or possibly some types of tubes are not good in triode 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.