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I do not really believe in the ultimate ability of SET amplifiers to drive loudspeakers, at least any loudspeakers. I am not talking about the impedance fluctuations or the inappropriately low impedance dives. Those are well know issues. The people who use 4R loudspeakers, that dive to 2.3R, drive them with SETs and then bitch that “the amp has no bass” are juts the Morons. There is another big problem with SETs that from my point of view make them not suitable for full range operation.

Genn wrote:

load for full range amp should be 1200 Ohm - that is very good for the tube and provides good damping.

The good damping for what? It is very very very frequently, practically always, that the MF and LF drivers (combined with the way how they implemented) would require different loading of the output tube. In my case the 6C33C loaded to 1200 Ohm and it is fine for my MF channels but I drive 6C33C much harder for LF channels (approximately 700R). It is not necessary has a lot of to do with 6C33C but with many other parameters that are external to amplifier. (For instant my LF speakers are superbly sensitive for damping and 50R of plate loading is quite auditable)

The point is that when people use SET for a full range then the by default introduce a huge compromise because the LF and MD simultaneously load the plate of the output stage. This is why I do not really believe that a SET might drive a full range inhalation. Usually SET does fine above 60Hz (with minimum capacitance in PS, and no compromise in transformer to accommodate the LF) and to go lower it needs another SET optimized for LF (with max capacitance in PC, oversized inductance on primary and exact LF loading of anode). This is where my rule of DSET (dedicated SET) was bourn…. A simple SET is just a MF amplifier….

The caT

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