My God all this is so incredibly complicated.
And after saying that, commentary herein is awfully impressive.
Tube amps - what 3 things…
I am close to purchasing a tube amp moving away from SS. So far I have listened to a pure sound, PL, and allnic.
Question for all you experienced owners - if you could do it all over again, what 3 things/features would you look for in an amplifier and what 3 things/features would you not invest in again?
I do not agree with this statement. The problem is that to do this properly, the output transformer (and the rest of the output circuit) has to be set up to handle the different operating points, and in practice this rarely happens.
If this is a concern, FWIW the original patent for ultralinear operation showed that the result had the same linearity of a triode with about 90% of the efficiency of a pentode output section. A lot of manufacturers realized the benefit, but to avoid paying the company that held the patent, moved the screen taps of the transformer to a slightly different spot, resulting in less linearity and simply called it good, thus bypassing the patent.
That patent has long since expired and the company that held it is unknown to most audiophiles and transformer manufacturers. As a result, its rare that the correct location of the screen tap on the winding is ever used. But if it were, ultralinear would be the only way to go if you are using an output transformer. Any competent transformer manufacturer could work this out though. Tradition of using the wrong position on the winding is literally the only thing stopping them!
Excellent point Ralph! Properly executed ultralinear topology is stunningly impressive. When executed properly, it is another reason why fixed (manually adjustable) output tube bias is essential, in order that output can be optimized for ultralinear topology.
So many short cuts are available in tube (well actually any) amplifier design that it is impossible to find a commercially available one that doesn't employ any of them. For example: does any manufacturer use an inductor filtered power supply instead of the much cheaper (and lighter) capacitance filtered power supply? None that I know of. The only way to get an absolutely uncompromised tube amplifier is to specifically requests such a build from a highly knowledgeable designer/builder, which will result in a very expensive and very heavy amplifier.
I'll refrain from exclaiming how extraordinarily special the amps I use are other than to state that they are the result of such a request.