SET vs Single Ended Parrallel

Has anyone compared directly a (single tube) Wavac 833 model to a similar output PSET (such as the Mastersound PF100 (four 845 tubes in parallel))?

As for my opinion - I haven't formed an informed one based on experience.

There are some very experienced and respected amp designers (Gordon Rankin) who swear there is a sonic penalty, and other firms (Audio Note) who build incredible parallel SETs and swear by that topology.

Brm1,

This question is not a matter of opinion at all. A parallel SET - single-ended-triode - amplifier IS A SET.

Note that I did NOT say that there are no sonic differences (penalties) associated with multiple output tubes. Many believe there are.

Paul,

I agree that, in terms of definition, parallel SET is an SET. But, the original poster is asking about what, if any sonic differences there are between use of one and more than one output tube. You are one of the most experienced poster so I, too, am interested in what you have heard.

Mike,

I suspect that choice of approach involves trading off compromises. PSET offers more power than using a single tube, but, it is more complex and difficult to implement. In the SET world, there is a bit of a "religion" when it comes to simpler is better. On the plus side for PSET, is the lower output impedance, but that advantage would probably require that the output transformer be designed to take advantage of the lower impedance.

I have been told that matching of tubes is extremely critical with PSET, particularly because of the problem of one tube ending up doing most of the work when an imbalance exists. In my amp, I've run the supposedly delicate EML meshplate 2a3s for a very long time. The tubes still sound good, though they now measure weak and quite grossly unbalanced in terms of transconductance (measured on an Amplitrex tube tester which tests at full power). Then again, I don't really push my amps very hard when playing them. So, I don't really know if this "issue" with PSET is really true, or if Audionote has a better implementation than some other designers, or I just don't really need the extra power of the PSET approach. All I know is that I heard, and preferred this amp over any other competitors.

Paul,

There would be many that disagree with you. If the signal is being amplified by more than one output tube per channel isn't there more room for error in the reproduction. I realize that there is no phase splitter, probably the biggest dif between SET/PP, but there has to be more issues than that doesn't there?
Thanks
Mike

Single-ended parallel is SET.

A SET is a SET regardless of the number of output tubes.

The only meaningful way to compare the sound of both approaches would be to hold as many other variables (apart from the number of tubes utilized) constant. However, there is a lot more to implementing parallel single-end. So, comparing any two amps utilizing the different approaches would not be definitive. For one thing, the parallel approach would reduce output impedance, so the ideal output transformer would require a lower turn ratio than that of a single tube SET.

I spoke to a designer who tried to implement the parallel approach and he could not solve the problem of one tube in a pair "hogging" and putting out most of the output. I have also heard that others who have tried this approach found that the sound is muddier when tubes are parallelled.

I haven't made a reasonable comparison myself, and I have no personal design knowledge. I do own a parallel singled ended amp -- the Audionote (uk) Kageki. This amp utilizes 2a3 tubes. To me, this is one of the better amps I have heard, in a variety of systems I've heard it in, provided that 6 watts is enough. But, I am NOT one who thinks only particular topologies work. I've also heard several terrific single tube SETs and pushpull amps as well. If I had to pick the single best amp I've heard, it would be an old Western Electric pushpull amp. Unfortunately, the amp I heard cost more than three times the price of a Kageki, and the Kageki is NOT cheap.