Triode mode vs pento mode

Triodes are some of the most linear amplification known to man. Pentodes are not and generally need negative feedback correct to be useful for audio.

Good bass has nothing to do with the amp being triode of pentode; good bass results from having the correct relationship to the speaker (see: http://www.atma-sphere.com/Resources/Paradigms_in_Amplifier_Design.php and proper bandwidth to play bass in the first place. That is not an issue between tube types.

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!

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.

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.

It depends entirely on how well the output transformer is designed. However if you caught some of my comments earlier about the actual correct tap point of the screen taps, if the transformer is really set up correctly there will be no need for triode mode at all, since a correct UL tap will have the same linearity.

IMO this is a bet that most manufacturers of UL output transformers have missed, on account of the fact that so many have for decades now put the tap in the wrong place in order to avoid patent infringement. As a result many designers today don't even *know* that there was even a patent- they think the wrong place for the tap is actually the right place :)