There are some theoretical problems with parallel SET topology. Some designers claim that it is hard to avoid one tube in a pair from becoming a "current hog" and seemingly end up doing most of the work while the other tube puts out much less output. There is also the claim that having multiple tube tends to make the sound less pure and a bit more "muddled" because the sound of the tubes is never perfectly matched (this would be an argument against ANY design with multiple devices providing the output).
I own a parallel SET amp (Audio Note Kageki). I like the sound so I cannot say whether these theoretical problems actually do affect performance. But, I will note that the output tubes do tend to become unbalanced over time, with one testing much stronger than the other in the pair for each channel.
The advantages of parallel output tubes in a SET are not only higher output. Using parallel tubes will also lower output impedance which means that damping factor will be increased or the designer can reduce the turn ratio between the primary and secondary windings of the output transformer.
I am guessing that there must be some challenges to making good parallel SET amps; my guess is based on the dearth of such designs on the market.
I would also dispute the notion that any particular design is inherently better than another. I've heard very fine examples of pushpull, SET and output transformerless amps (OTL). The amp I currently favor in my system is a pushpull amp (I still do like the Kageki, which I have loaned to a friend). One of my all time favorite amp is an OTL amp.
I own a parallel SET amp (Audio Note Kageki). I like the sound so I cannot say whether these theoretical problems actually do affect performance. But, I will note that the output tubes do tend to become unbalanced over time, with one testing much stronger than the other in the pair for each channel.
The advantages of parallel output tubes in a SET are not only higher output. Using parallel tubes will also lower output impedance which means that damping factor will be increased or the designer can reduce the turn ratio between the primary and secondary windings of the output transformer.
I am guessing that there must be some challenges to making good parallel SET amps; my guess is based on the dearth of such designs on the market.
I would also dispute the notion that any particular design is inherently better than another. I've heard very fine examples of pushpull, SET and output transformerless amps (OTL). The amp I currently favor in my system is a pushpull amp (I still do like the Kageki, which I have loaned to a friend). One of my all time favorite amp is an OTL amp.