Triode mode vs pento mode

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.

Thanks for the info. What do you think of the amps that allow for a switch between UL and triode? Are they somewhat "compromised" for the sake of flexibility?

I understand your designs tend to avoid transformers completely and I had the pleasure of listening to old MA1s some 20 years ago.

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 :)