Posted by Thermionic [ 74.194.144.58 ] on November 08, 2007 at 14:12:02:

In Reply to: Re: Cathode Follower SET Amp posted by real_one on November 02, 2007 at 11:11:44:

Indeed. Depending on the low frequency cutoff points throughout the amp, and the output transformer design and its reflected impedance ratio, a SE amp can reach flat to below 40Hz.

What the manufacturer doesn't mention is the one great inherit drawback of cathode follower output stages. Cathode followers have less than unity gain, so 100% of the voltage swing must come exclusively from the small signal stages. Most any small signal stage's distortion spectrum will be weighted heavier towards high order harmonics than a DHT power triode using a "traditional" output transformer output coupled configuration. This is especially true for cascode stages, and other super high gain small signal stages capable of such large voltage swings. Even a voltage amplifier stage using highly linear, low mu small signal triodes cascaded together won't be low distortion any longer by the time it has to swing a few hundred volts. There's a good reason why cathode follower output stages aren't more popular.

Thermionic

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